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1
Yang, Xiaolei, Daniel Foti, Christopher Kelley, David Maniaci, and Fotis Sotiropoulos. "Wake Statistics of Different-Scale Wind Turbines under Turbulent Boundary Layer Inflow." Energies 13, no. 11 (2020): 3004. http://dx.doi.org/10.3390/en13113004.
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Subscale wind turbines can be installed in the field for the development of wind technologies, for which the blade aerodynamics can be designed in a way similar to that of a full-scale wind turbine. However, it is not clear whether the wake of a subscale turbine, which is located closer to the ground and faces different incoming turbulence, is also similar to that of a full-scale wind turbine. In this work we investigate the wakes from a full-scale wind turbine of rotor diameter 80 m and a subscale wind turbine of rotor diameter of 27 m using large-eddy simulation with the turbine blades and nacelle modeled using actuator surface models. The blade aerodynamics of the two turbines are the same. In the simulations, the two turbines also face the same turbulent boundary inflows. The computed results show differences between the two turbines for both velocity deficits and turbine-added turbulence kinetic energy. Such differences are further analyzed by examining the mean kinetic energy equation.
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Zhang, Weihao, and Zhengping Zou. "Large eddy simulations of periodic wake effects on boundary-layer transition of low-pressure turbine cascades." AIP Advances 13, no. 2 (2023): 025128. http://dx.doi.org/10.1063/5.0139787.
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The periodic wake effect is one of the most important sources of unsteady disturbance in turbines. Its influence on the boundary layer transition process of the downstream blade suction surface is an important factor determining the turbine loss and aerodynamic performance, and also an effective potential approach of turbine loss control. In this paper, the high-load low-pressure turbine (LPT) cascade is taken as the research object, and the large eddy simulation based on the inhouse coed Multiblock Parallel Large-eddy Simulation is used to study the periodic influence of upstream wake. The unsteady transition process of the boundary layer on the suction surface of the turbine cascade and the spatial–temporal evolution of the vortex are discussed in detail. It is shown that there are three modes of boundary layer transition on the suction surface of the LPT cascade under the effect of wake, occurring alternately during the wake passing period. Each mode of transition has different characteristics in vortex structures, as well as boundary-layer separation and reattachment, thereby makes different losses. Although the transition mechanism and evolution process of the three modes are different, the calming regions exist in all three modes, which is important for the control of the boundary layer. This study gives an important reference for reducing the flow loss in high-load turbines by means of periodic wakes.
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Halim, Sufi, Md Tasyrif Abdul Rahman, Anas Abdul Rahman, et al. "Influence of Outlets Port Design on The Tesla Turbine Performance." Journal of Physics: Conference Series 2129, no. 1 (2021): 012074. http://dx.doi.org/10.1088/1742-6596/2129/1/012074.
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Abstract The boundary layer turbine known as Tesla Turbine invented long ago but has failed to be commercialized and replaced by bladed turbines. In this paper, two new techniques for improving the turbine have been proposed. A test model of the proposed boundary layer turbine has been fabricated made and tested under different conditions. The design process includes producing a virtual design and simulation of the turbine using computer software. The proposed designs were fabricated and then tested to analyse results such as speed produced, power produced, and the turbine efficiency. From this study, the proposed turbine designs manage to achieve 18% and 69% efficiency. The findings of this study will serve as a reference for future studies in the generation of power through an alternative powered driven turbine.
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Ali, N., G. Cortina, N. Hamilton, M. Calaf, and R. B. Cal. "Turbulence characteristics of a thermally stratified wind turbine array boundary layer via proper orthogonal decomposition." Journal of Fluid Mechanics 828 (August 31, 2017): 175–95. http://dx.doi.org/10.1017/jfm.2017.492.
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A large eddy simulation framework is used to explore the structure of the turbulent flow in a thermally stratified wind turbine array boundary layer. The flow field is driven by a constant geostrophic wind with time-varying surface boundary conditions obtained from a selected period of the CASES-99 field experiment. Proper orthogonal decomposition is used to extract coherent structures of the turbulent flow under the considered thermal stratification regimes. The flow structure is discussed in the context of three-dimensional representations of key modes, which demonstrate features ranging in size from the wind turbine wakes to the atmospheric boundary layer. Results demonstrate that structures related to the atmospheric boundary layer flow dominate over those introduced by the wind farm for the unstable and neutrally stratified regimes; large structures in atmospheric turbulence are beneficial for the wake recovery, and consequently the presence of the turbulent wind turbine wakes is diminished. Contrarily, the flow in the stably stratified case is fully dominated by the presence of the turbines and highly influenced by the Coriolis force. A comparative analysis of the test cases indicates that during the stable regime, higher-order modes contribute less to the overall character of the flow. Under neutral and unstable stratification, important turbulence dynamics are distributed over a larger range of basis functions. The influence of the wind turbines on the structure of the atmospheric boundary layer is mainly quantified via the turbulence kinetic energy of the first ten modes. Linking the new insights into structure of the wind turbine/atmospheric boundary layer and their interaction addressed here will benefit the formulation of new simplified models for commercial application.
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Gans, F., L. M. Miller, and A. Kleidon. "The problem of the second wind turbine – a note on a common but flawed wind power estimation method." Earth System Dynamics 3, no. 1 (2012): 79–86. http://dx.doi.org/10.5194/esd-3-79-2012.
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Abstract. Several recent wind power estimates suggest that this renewable energy resource can meet all of the current and future global energy demand with little impact on the atmosphere. These estimates are calculated using observed wind speeds in combination with specifications of wind turbine size and density to quantify the extractable wind power. However, this approach neglects the effects of momentum extraction by the turbines on the atmospheric flow that would have effects outside the turbine wake. Here we show with a simple momentum balance model of the atmospheric boundary layer that this common methodology to derive wind power potentials requires unrealistically high increases in the generation of kinetic energy by the atmosphere. This increase by an order of magnitude is needed to ensure momentum conservation in the atmospheric boundary layer. In the context of this simple model, we then compare the effect of three different assumptions regarding the boundary conditions at the top of the boundary layer, with prescribed hub height velocity, momentum transport, or kinetic energy transfer into the boundary layer. We then use simulations with an atmospheric general circulation model that explicitly simulate generation of kinetic energy with momentum conservation. These simulations show that the assumption of prescribed momentum import into the atmospheric boundary layer yields the most realistic behavior of the simple model, while the assumption of prescribed hub height velocity can clearly be disregarded. We also show that the assumptions yield similar estimates for extracted wind power when less than 10% of the kinetic energy flux in the boundary layer is extracted by the turbines. We conclude that the common method significantly overestimates wind power potentials by an order of magnitude in the limit of high wind power extraction. Ultimately, environmental constraints set the upper limit on wind power potential at larger scales rather than detailed engineering specifications of wind turbine design and placement.
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Kovalnogov, Vladislav N., Ruslan V. Fedorov, Andrei V. Chukalin, Ekaterina V. Tsvetova, and Mariya I. Kornilova. "Modeling and Investigation of the Effect of a Wind Turbine on the Atmospheric Boundary Layer." Energies 15, no. 21 (2022): 8196. http://dx.doi.org/10.3390/en15218196.
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Wind power engineering is one of the environmentally safe areas of energy and certainly makes a significant contribution to the fight against CO2 emissions. The study of the air masses movement in the zone of wind turbines and their influence on the boundary layer of the atmosphere is a fundamental basis for the efficient use of wind energy. The paper considers the theory of the movement of air masses in the rotation zone of a wind turbine, and presents an analytical review of applied methods for modeling the atmospheric boundary layer and its interaction with a wind turbine. The results of modeling the boundary layer in the wind turbine zone using the STAR CCM+ software product are presented. The wind speed and intensity of turbulence in the near and far wake of the wind turbine at nominal load parameters are investigated. There is a significant decrease in the average wind speed in the near wake of the wind generator by 3 m/s and an increase in turbulent intensity by 18.3%. When considering the long-distance track behind the wind turbine, there is a decrease in the average speed by 0.6 m/s, while the percentage taken from the average value of the turbulent intensity is 7.2% higher than in the section in front of the wind generator. The influence of a wind turbine on the change in the temperature stratification of the boundary layer is considered. The experiments revealed a temperature change (up to 0.5 K), which is insignificant, but at night the stratification reaches large values due to an increase in the temperature difference in the surface boundary layer. In the long term, the research will contribute to the sustainable and efficient development of regional wind energy.
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Howell, R. J., H. P. Hodson, V. Schulte, et al. "Boundary Layer Development in the BR710 and BR715 LP Turbines—The Implementation of High-Lift and Ultra-High-Lift Concepts." Journal of Turbomachinery 124, no. 3 (2002): 385–92. http://dx.doi.org/10.1115/1.1457455.
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This paper describes a detailed study into the unsteady boundary layer behavior in two high-lift and one ultra-high-lift Rolls-Royce Deutschland LP turbines. The objectives of the paper are to show that high-lift and ultra-high-lift concepts have been successfully incorporated into the design of these new LP turbine profiles. Measurements from surface mounted hot film sensors were made in full size, cold flow test rigs at the altitude test facility at Stuttgart University. The LP turbine blade profiles are thought to be state of the art in terms of their lift and design philosophy. The two high-lift profiles represent slightly different styles of velocity distribution. The first high-lift profile comes from a two-stage LP turbine (the BR710 cold-flow, high-lift demonstrator rig). The second high-lift profile tested is from a three-stage machine (the BR715 LPT rig). The ultra-high-lift profile measurements come from a redesign of the BR715 LP turbine: this is designated the BR715UHL LP turbine. This ultra-high-lift profile represents a 12 percent reduction in blade numbers compared to the original BR715 turbine. The results from NGV2 on all of the turbines show “classical” unsteady boundary layer behavior. The measurements from NGV3 (of both the BR715 and BR715UHL turbines) are more complicated, but can still be broken down into classical regions of wake-induced transition, natural transition and calming. The wakes from both upstream rotors and NGVs interact in a complicated manner, affecting the suction surface boundary layer of NGV3. This has important implications for the prediction of the flows on blade rows in multistage environments.
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Ali, Naseem, Nicholas Hamilton, Dominic DeLucia, and Raúl Bayoán Cal. "Assessing spacing impact on coherent features in a wind turbine array boundary layer." Wind Energy Science 3, no. 1 (2018): 43–56. http://dx.doi.org/10.5194/wes-3-43-2018.
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Abstract. As wind farms become larger, the spacing between turbines becomes a significant design consideration that can impose serious economic constraints. To investigate the turbulent flow structures in a 4 × 3 Cartesian wind turbine array boundary layer (WTABL), a wind tunnel experiment was carried out parameterizing the streamwise and spanwise wind turbine spacing. Four cases are chosen spacing turbines by 6 or 3D in the streamwise direction, and 3 or 1.5D in the spanwise direction, where D = 12 cm is the rotor diameter. Data are obtained experimentally using stereo particle image velocimetry. Mean streamwise velocity showed maximum values upstream of the turbine with the spacing of 6 and 3D in the streamwise and spanwise direction, respectively. Fixing the spanwise turbine spacing to 3D, variations in the streamwise spacing influence the turbulent flow structure and the power available to following wind turbines. Quantitative comparisons are made through spatial averaging, shifting measurement data and interpolating to account for the full range between devices to obtain data independent of array spacing. The largest averaged Reynolds stress is seen in cases with spacing of 3D × 3D. Snapshot proper orthogonal decomposition (POD) was employed to identify the flow structures based on the turbulence kinetic energy content. The maximum turbulence kinetic energy content in the first POD mode is seen for turbine spacing of 6D × 1.5D. The flow upstream of each wind turbine converges faster than the flow downstream according to accumulation of turbulence kinetic energy by POD modes, regardless of spacing. The streamwise-averaged profile of the Reynolds stress is reconstructed using a specific number of modes for each case; the case of 6D × 1.5D spacing shows the fastest reconstruction to compare the rate of reconstruction of statistical profiles. Intermediate modes are also used to reconstruct the averaged profile and show that the intermediate scales are responsible for features seen in the original profile. The variation in streamwise and spanwise spacing leads to changes in the background structure of the turbulence, where the color map based on barycentric map and Reynolds stress anisotropy tensor provides an alternate perspective on the nature of the perturbations within the wind turbine array. The impact of the streamwise and spanwise spacings on power produced is quantified, where the maximum production corresponds with the case of greatest turbine spacing.
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Goit, Jay P., and Johan Meyers. "Optimal control of energy extraction in wind-farm boundary layers." Journal of Fluid Mechanics 768 (February 27, 2015): 5–50. http://dx.doi.org/10.1017/jfm.2015.70.
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In very large wind farms, the vertical interaction with the atmospheric boundary layer plays an important role, i.e. the total energy extraction is governed by the vertical transport of kinetic energy from higher regions in the boundary layer towards the turbine level. In the current study, we investigate optimal control of wind-farm boundary layers, considering the individual wind turbines as flow actuators, whose energy extraction can be dynamically regulated in time so as to optimally influence the flow field and the vertical energy transport. To this end, we use large-eddy simulations of a fully developed pressure-driven wind-farm boundary layer in a receding-horizon optimal control framework. For the optimization of the wind-turbine controls, a conjugate-gradient optimization method is used in combination with adjoint large-eddy simulations for the determination of the gradients of the cost functional. In a first control study, wind-farm energy extraction is optimized in an aligned wind farm. Results are accumulated over one hour of operation. We find that the energy extraction is increased by 16 % compared to the uncontrolled reference. This is directly related to an increase of the vertical fluxes of energy towards the wind turbines, and vertical shear stresses increase considerably. A further analysis, decomposing the total stresses into dispersive and Reynolds stresses, shows that the dispersive stresses increase drastically, and that the Reynolds stresses decrease on average, but increase in the wake region, leading to better wake recovery. We further observe also that turbulent dissipation levels in the boundary layer increase, and overall the outer layer of the boundary layer enters into a transient decelerating regime, while the inner layer and the turbine region attain a new statistically steady equilibrium within approximately one wind-farm through-flow time. Two additional optimal control cases study penalization of turbulent dissipation. For the current wind-farm geometry, it is found that the ratio between wind-farm energy extraction and turbulent boundary-layer dissipation remains roughly around 70 %, but can be slightly increased by a few per cent by penalizing the dissipation in the optimization objective. For a pressure-driven boundary layer in equilibrium, we estimate that such a shift can lead to an increase in wind-farm energy extraction of 6 %.
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Özgen, Serkan, Eda Bahar Sarıbel, and Ali Rıza Yaman. "Effect of blade contamination on power production of wind turbines." Journal of Physics: Conference Series 2265, no. 3 (2022): 032012. http://dx.doi.org/10.1088/1742-6596/2265/3/032012.
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Abstract Wind turbines suffer from considerable power losses because of contamination on their blades, that can be due to erosion, wear, smog, insect, sand and dust particle impact. Blade contamination, its effects on the flows over the wind turbine blades and consequent power production losses form the main focus of the present study. These effects are mainly due to increased roughness on the blades leading to earlier laminar-turbulent transition and consequently, thicker boundary-layers on the blades. Early laminar-turbulent transition leads to a larger part of the flow over a blade being turbulent, thus increasing skin friction drag. Thicker boundary-layer on a blade results in blade profile being effectively modified, rendering the flow over the blade depart from ideal. In the present study, the effects of blade contamination on power output of contaminated wind turbine blades is investigated numerically using an in-house computational tool. Blade Element Momentum Method (BEM) combined with the Panel Method is used to calculate the local velocity and angle of attack at the blade sections, together with the power produced by the blade. Trajectories of particles causing contamination are calculated using Lagrangian approach, also yielding the impingement pattern of the particles on the blade surface, i.e. particle collection efficiency distribution. The effects of roughness on the boundary-layer flow are investigated by using an Integral Boundary-Layer Method, which yields the characteristics of the boundary-layer, i.e. laminar-turbulent transition location, increased skin-friction and thickening of the boundary-layer. The blade shape is modified due contamination thickness, the local height of which is assumed to be proportional to the local collection efficiency. Also, the roughness height distribution used in the boundary-layer calculations is assumed to be equal to the contamination thickness distribution on the blades. Power production and consequent losses of wind turbines with contaminated wind turbine blades are studied with respect to variations in particle size, wind speed and roughness height.
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Xu, Qingzong, Pei Wang, Qiang Du, Jun Liu, and Guang Liu. "Effects of axial length and integrated design on the aggressive intermediate turbine duct." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 233, no. 4 (2018): 443–56. http://dx.doi.org/10.1177/0957650918797450.
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With the increasing demand of high bypass ratio and thrust-to-weight ratio in civil aero-engine, the intermediate turbine duct between the high pressure and low pressure turbines of a modern gas turbine tends to shorter axial length, larger outlet-to-inlet area ratio and high pressure-to-low pressure radial offset. This paper experimentally and numerically investigated the three-dimensional flow characteristics of traditional (ITD1) and aggressive intermediate turbine duct (ITD2) at low Reynolds number. The baseline case of ITD1 is representative of a traditional intermediate turbine duct of aero-engine design with non-dimensional length of L/dR = 2.79 and middle angle of 20.12°. The detailed flow fields inside ITD1 and flow visualization were measured. Results showed the migration of boundary layer and a pair of counter-rotating vortexes were formed due to the radial migration of low momentum fluid. With the decreasing axial length of intermediate turbine duct, the radial and streamwise reverse pressure gradient in aggressive intermediate turbine duct (ITD2) were increased resulting in severe three-dimensional separation of boundary layer near casing surface and higher total pressure loss. The secondary flow and separation of boundary layer near the endwall were deeply analyzed to figure out the main source of high total pressure loss in the aggressive intermediate turbine duct (ITD2). Based on that, employing wide-chord guide vane to substitute “strut + guide vane”, this paper designed the super-aggressive intermediate turbine duct and realized the suppression of the three-dimensional separation and secondary flow.
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AbdelSalam, Ali M., and Ramalingam Velraj. "umerical simulation of atmospheric boundary layer and wakes of horizontal-axis wind turbines." Journal of Energy in Southern Africa 25, no. 1 (2014): 44–50. http://dx.doi.org/10.17159/2413-3051/2014/v25i1a2687.
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Simulations of wind turbine wakes are presented in this paper using the three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations employing the k-e turbulence model appropriately modified for the atmospheric flows. The actuator disk approach is used to model the action of the turbine rotor. Modified formulations of the inlet conditions and the wall functions are used to allow consistency between the fully developed atmospheric boundary layer (ABL) inlet profiles and the wall function formulation. Results are presented and compared with three wind turbines running under neutral atmospheric conditions. The results demonstrate that the accurate simulation of the atmospheric boundary layer applying enhanced inlet conditions and wall function formulation consistent with the k-e model can give very useful information about the wakes, directly contributing to the accurate estimation of the power of the downstream turbines.
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Al-Shnynat, Nidal, and Hamzeh Duwairi. "The effects of turbulent air streams and corrugated surfaces on the output of a wind turbine." Advances in Mechanical Engineering 14, no. 5 (2022): 168781322210959. http://dx.doi.org/10.1177/16878132221095916.
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It is challenging to select the area that best fit the installation of wind turbines within complex and forestry terrains. This study aims to highlight the effects of corrugated surfaces on the characteristics of a turbulent wind flow, and on the performance of a wind turbine installed within this topography. It is hypothesized that a sinusoidal wave can be utilized to describe a corrugated surface. The physical stance was analytically modeled based on conservation principles of mass and mechanical energy. Model’s mathematical equation was then solved, by adopting finite difference method and MATLAB’s Bvp4c algorithm. The results show that wind and turbine related parameters are affected by the evolved atmospheric Boundary Layer (ABL) and differed according to the location within the boundary layer (BL) from the leading part to the edge, where BL’s retarding effects diminishes. The study also proves that velocity and turbine harvested power are inversely proportional to the corrugated surface’s amplitude, and to the wind’s turbulence ratio. On the other hand, it demonstrates a direct proportion between boundary layer thickness (BLT) and corrugated surfaces-related parameters. To the contrary of previous works, this study concentrated on capturing interaction effects between wind turbine, atmospheric inflow, and complex terrains.
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Cossu, Carlo. "Evaluation of tilt control for wind-turbine arrays in the atmospheric boundary layer." Wind Energy Science 6, no. 3 (2021): 663–75. http://dx.doi.org/10.5194/wes-6-663-2021.
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Abstract. Wake redirection is a promising approach designed to mitigate turbine–wake interactions which have a negative impact on the performance and lifetime of wind farms. It has recently been found that substantial power gains can be obtained by tilting the rotors of spanwise-periodic wind-turbine arrays. Rotor tilt is associated with the generation of coherent streamwise vortices which deflect wakes towards the ground and, by exploiting the vertical wind shear, replace them with higher-momentum fluid (high-speed streaks). The objective of this work is to evaluate power gains that can be obtained by tilting rotors in spanwise-periodic wind-turbine arrays immersed in the atmospheric boundary layer and, in particular, to analyze the influence of the rotor size on power gains in the case where the turbines emerge from the atmospheric surface layer. We show that, for the case of wind-aligned arrays, large power gains can be obtained for positive tilt angles of the order of 30∘. Power gains are substantially enhanced by operating tilted-rotor turbines at thrust coefficients higher than in the reference configuration. These power gains initially increase with the rotor size reaching a maximum for rotor diameters of the order of 3.6 boundary layer momentum thicknesses (for the considered cases) and decrease for larger sizes. Maximum power gains are obtained for wind-turbine spanwise spacings which are very similar to those of large-scale and very-large-scale streaky motions which are naturally amplified in turbulent boundary layers. These results are all congruent with the findings of previous investigations of passive control of canonical boundary layers for drag-reduction applications where high-speed streaks replaced wakes of spanwise-periodic rows of wall-mounted roughness elements.
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Stieger, R. D., and H. P. Hodson. "Unsteady dissipation measurements on a flat plate subject to wake passing." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 217, no. 4 (2003): 413–19. http://dx.doi.org/10.1243/095765003322315478.
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Boundary layer measurements were performed on a flat plate with an imposed pressure gradient typical of a high-lift low-pressure (LP) turbine blade and subject to incoming turbulent wakes shed from a moving bar wake generator. A multiple-orientation one-dimensional laser doppler anemometry (LDA) technique was used to measure the ensemble-average mean flow and Reynolds stresses. These ensembleaverage measurements were used to calculate the boundary layer dissipation, thereby providing unprecedented experimental evidence of the loss-reducing mechanisms associated with wake-induced transition. The benign character of the calmed zone was confirmed and the early stages of boundary layer separation were found to have laminar levels of dissipation. A deterministic natural transition phenomenon was identified between wake passing events, highlighting the existence of natural transition phenomena in LP turbine style pressure distributions.
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Debnath, M., C. Santoni, S. Leonardi, and G. V. Iungo. "Towards reduced order modelling for predicting the dynamics of coherent vorticity structures within wind turbine wakes." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, no. 2091 (2017): 20160108. http://dx.doi.org/10.1098/rsta.2016.0108.
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The dynamics of the velocity field resulting from the interaction between the atmospheric boundary layer and a wind turbine array can affect significantly the performance of a wind power plant and the durability of wind turbines. In this work, dynamics in wind turbine wakes and instabilities of helicoidal tip vortices are detected and characterized through modal decomposition techniques. The dataset under examination consists of snapshots of the velocity field obtained from large-eddy simulations (LES) of an isolated wind turbine, for which aerodynamic forcing exerted by the turbine blades on the atmospheric boundary layer is mimicked through the actuator line model. Particular attention is paid to the interaction between the downstream evolution of the helicoidal tip vortices and the alternate vortex shedding from the turbine tower. The LES dataset is interrogated through different modal decomposition techniques, such as proper orthogonal decomposition and dynamic mode decomposition. The dominant wake dynamics are selected for the formulation of a reduced order model, which consists in a linear time-marching algorithm where temporal evolution of flow dynamics is obtained from the previous temporal realization multiplied by a time-invariant operator. This article is part of the themed issue ‘Wind energy in complex terrains’.
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Halstead, D. E., D. C. Wisler, T. H. Okiishi, G. J. Walker, H. P. Hodson, and H. W. Shin. "Boundary Layer Development in Axial Compressors and Turbines: Part 1 of 4—Composite Picture." Journal of Turbomachinery 119, no. 1 (1997): 114–27. http://dx.doi.org/10.1115/1.2841000.
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Comprehensive experiments and computational analyses were conducted to understand boundary layer development on airfoil surfaces in multistage, axial-flow compressors and LP turbines. The tests were run over a broad range of Reynolds numbers and loading levels in large, low-speed research facilities which simulate the relevant aerodynamic features of modern engine components. Measurements of boundary layer characteristics were obtained by using arrays of densely packed, hot-film gauges mounted on airfoil surfaces and by making boundary layer surveys with hot wire probes. Computational predictions were made using both steady flow codes and an unsteady flow code. This is the first time that time-resolved boundary layer measurements and detailed comparisons of measured data with predictions of boundary layer codes have been reported for multistage compressor and turbine blading. Part 1 of this paper summarizes all of our experimental findings by using sketches to show how boundary layers develop on compressor and turbine blading. Parts 2 and 3 present the detailed experimental results for the compressor and turbine, respectively. Part 4 presents computational analyses and discusses comparisons with experimental data. Readers not interested in experimental detail can go directly from Part 1 to Part 4. For both compressor and turbine blading, the experimental results show large extents of laminar and transitional flow on the suction surface of embedded stages, with the boundary layer generally developing along two distinct but coupled paths. One path lies approximately under the wake trajectory while the other lies between wakes. Along both paths the boundary layer clearly goes from laminar to transitional to turbulent. The wake path and the non-wake path are coupled by a calmed region, which, being generated by turbulent spots produced in the wake path, is effective in suppressing flow separation and delaying transition in the non-wake path. The location and strength of the various regions within the paths, such as wake-induced transitional and turbulent strips, vary with Reynolds number, loading level, and turbulence intensity. On the pressure surface, transition takes place near the leading edge for the blading tested. For both surfaces, bypass transition and separated-flow transition were observed. Classical Tollmien–Schlichting transition did not play a significant role. Comparisons of embedded and first-stage results were also made to assess the relevance of applying single-stage and cascade studies to the multistage environment. Although doing well under certain conditions, the codes in general could not adequately predict the onset and extent of transition in regions affected by calming. However, assessments are made to guide designers in using current predictive schemes to compute boundary layer features and obtain reasonable loss predictions.
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Viqueira-Moreira, Manuel, and Esteban Ferrer. "Insights into the Aeroacoustic Noise Generation for Vertical Axis Turbines in Close Proximity." Energies 13, no. 16 (2020): 4148. http://dx.doi.org/10.3390/en13164148.
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We present Large Eddy Simulations and aeroacoustic spectra for three configurations of increasing flow complexity: an isolated NACA0012 airfoil, an isolated rotating vertical axis wind turbine composed of three rotating airfoils and a farm of four vertical axis turbines (with identical characteristics as the isolated turbine), which are located in close proximity. The aeroacoustic signatures of the simulated airfoil and the isolated turbine are validated using published numerical and experimental data. We provide theoretical estimates to predict tonal frequencies, which are used to identify the main physical mechanisms responsible for the tonal signature and for each configuration and enable the categorisation of the main tonal aeroacoustic sources of vertical axis turbines operating in close proximity. Namely, we identify wake, vortex, blade passing and boundary layer phenomena and provide estimates for the associated tonal frequencies, which are validated with simulations. In the farm, we observe non-linear interactions and enhanced mixing that decreases tonal frequencies in favour of larger broadband amplitudes at low frequencies. Comparing the spectrum with that of the isolated turbine, only the blade passing frequency and the boundary layer tones can be clearly identified. Variations in acoustic amplitudes, tonal frequencies and sound directivities suggest that a linear combination of sources from isolated turbines is not enough to characterise the aeroacoustic footprint of vertical axiswind turbines located in close proximity, and that farms need to be considered and studied as different entities.
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Zhu, Wei Jun, Nicolai Heilskov, Wen Zhong Shen, and Jens Nørkær Sørensen. "Modeling of Aerodynamically Generated Noise From Wind Turbines." Journal of Solar Energy Engineering 127, no. 4 (2005): 517–28. http://dx.doi.org/10.1115/1.2035700.
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A semiempirical acoustic generation model based on the work of Brooks, Pope, and Marcolini [NASA Reference Publication 1218 (1989)] has been developed to predict aerodynamic noise from wind turbines. The model consists of dividing the blades of the wind turbine into two-dimensional airfoil sections and predicting the total noise emission as the sum of the contribution from each blade element. Input is the local relative velocities and boundary layer parameters. These quantities are obtained by combining the model with a Blade Element Momentum (BEM) technique to predict local inflow characteristics to the blades. Boundary layer characteristics are determined from two-dimensional computations of airfoils. The model is applied to the Bonus 300 kW wind turbine at a wind speed of 8 m/s. Comparisons of total noise spectra show good agreement with experimental data.
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MATSUNUMA, Takayuki, Hiro YOSHIDA, and Yasukata TSUTSUI. "Boundary Layer Control of an Annular Turbine Cascade." Proceedings of the JSME annual meeting 2004.3 (2004): 345–46. http://dx.doi.org/10.1299/jsmemecjo.2004.3.0_345.
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Dumitrescu, H., and V. Cardoş. "Inboard boundary layer state on wind turbine blades." ZAMM 89, no. 3 (2009): 163–73. http://dx.doi.org/10.1002/zamm.200800105.
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Dumitrescu, Horia, and Vladimir Cardos. "Three-dimensional boundary layer on wind turbine blades." PAMM 4, no. 1 (2004): 432–33. http://dx.doi.org/10.1002/pamm.200410197.
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Hara, K., M. Furukawa, and M. Inoue. "Behavior of Three-Dimensional Boundary Layers in a Radial Inflow Turbine Scroll." Journal of Turbomachinery 116, no. 3 (1994): 446–52. http://dx.doi.org/10.1115/1.2929431.
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A detailed experimental investigation was carried out to examine the three-dimensional boundary layer characteristics in a radial inflow turbine scroll. Some basic flow phenomena and growth of secondary flow were also investigated. In the inlet region of the scroll, the incoming boundary layer begins to have a skewed nature, namely the radially inward secondary flow caused by the radial pressure gradient. From the inlet region to one third of the scroll circumference, the secondary flow grows so strongly that most of the low-momentum fluid in the incoming boundary layer is transported to the nozzle region. The succeeding elimination of the low-momentum fluid in the boundary layer suppresses growth of the boundary layer farther downstream, where the boundary layer shows a similar velocity profile. The distributions of the boundary layer properties in the scroll correspond well to those of the flow properties at the nozzle. The behavior of the boundary layer in the scroll is found to affect the circumferential nonuniformity of the nozzle flow field.
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Allaerts, Dries, and Johan Meyers. "Boundary-layer development and gravity waves in conventionally neutral wind farms." Journal of Fluid Mechanics 814 (February 6, 2017): 95–130. http://dx.doi.org/10.1017/jfm.2017.11.
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While neutral atmospheric boundary layers are rare over land, they occur frequently over sea. In these cases they are almost always of the conventionally neutral type, in which the neutral boundary layer is capped by a strong inversion layer and a stably stratified atmosphere aloft. In the current study, we use large-eddy simulations (LES) to investigate the interaction between a large wind farm that has a fetch of 15 km and a conventionally neutral boundary layer (CNBL) in typical offshore conditions. At the domain inlet, we consider three different equilibrium CNBLs with heights of approximately 300 m, 500 m and 1000 m that are generated in a separate precursor LES. We find that the height of the inflow boundary layer has a significant impact on the wind farm flow development. First of all, above the farm, an internal boundary layer develops that interacts downwind with the capping inversion for the two lowest CNBL cases. Secondly, the upward displacement of the boundary layer by flow deceleration in the wind farm excites gravity waves in the inversion layer and the free atmosphere above. For the lower CNBL cases, these waves induce significant pressure gradients in the farm (both favourable and unfavourable depending on location and case). A detailed energy budget analysis in the turbine region shows that energy extracted by the wind turbines comes both from flow deceleration and from vertical turbulent entrainment. Though turbulent transport dominates near the end of the farm, flow deceleration remains significant, i.e. up to 35 % of the turbulent flux for the lowest CNBL case. In fact, while the turbulent fluxes are fully developed after eight turbine rows, the mean flow does not reach a stationary regime. A further energy budget analysis over the rest of the CNBL reveals that all energy available at turbine level comes from upwind kinetic energy in the boundary layer. In the lower CNBL cases, the pressure field induced by gravity waves plays an important role in redistributing this energy throughout the farm. Overall, in all cases entrainment at the capping inversion is negligible, and also the work done by the mean background pressure gradient, arising from the geostrophic balance in the free atmosphere, is small.
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de la Blanco, E. Rosa, H. P. Hodson, R. Vazquez, and D. Torre. "Influence of the state of the inlet endwall boundary layer on the interaction between pressure surface separation and endwall flows." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 217, no. 4 (2003): 433–41. http://dx.doi.org/10.1243/095765003322315496.
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This paper describes the effect of the state of the inlet boundary layer (laminar or turbulent) on the structure of the endwall flow on two different profiles of low-pressure (LP) turbine blades (solid thin and hollow thick). At present the state of the endwall boundary layer at the inlet of a real LP turbine is not known. The intention of this paper is to show that, for different designs of LP turbine, the state of the inlet boundary layer affects the performance of the blade in very different ways. The testing was completed at low speed in a linear cascade using area traversing, flow visualization and static pressure measurements. The paper shows that, for a laminar inlet boundary layer the two profiles have a similar loss distribution and structure of endwall flow. However, for a turbulent inlet boundary layer the two profiles are shown to differ significantly in both the total loss and endwall flow structure. The pressure side separation bubble on the solid thin profile is shown to interact with the passage vortex, causing a higher endwall loss than that measured on the hollow thick profile.
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Rajewski, Daniel A., Eugene S. Takle, Julie K. Lundquist, et al. "Crop Wind Energy Experiment (CWEX): Observations of Surface-Layer, Boundary Layer, and Mesoscale Interactions with a Wind Farm." Bulletin of the American Meteorological Society 94, no. 5 (2013): 655–72. http://dx.doi.org/10.1175/bams-d-11-00240.1.
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Perturbations of mean and turbulent wind characteristics by large wind turbines modify fluxes between the vegetated surface and the lower boundary layer. While simulations have suggested that wind farms could significantly change surface fluxes of heat, momentum, momentum, moisture, and CO2 over hundreds of square kilometers, little observational evidence exists to test these predictions. Quantifying the influences of the “turbine layer” is necessary to quantify how surface fluxes are modified and to better forecast energy production by a wind farm. Changes in fluxes are particularly important in regions of intensely managed agriculture where crop growth and yield are highly dependent on subtle changes in moisture, heat, and CO2. Furthermore, speculations abound about the possible mesoscale consequences of boundary layer changes that are produced by wind farms. To address the lack of observations to answer these questions, we developed the Crop Wind Energy Experiment (CWEX) as a multiagency, multiuniversity field program in central Iowa. Throughout the summer of 2010, surface fluxes were documented within a wind farm test site and a 2-week deployment of a vertically pointing lidar quantified wind profiles. In 2011, we expanded measurements at the site by deploying six flux stations and two wind-profiling lidars to document turbine wakes. The results provide valuable insights into the exchanges over a surface that has been modified by wind turbines and a basis for a more comprehensive measurement program planned for the summer in 2014.
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Lu, Xingen, Yanfeng Zhang, Wei Li, Shuzhen Hu, and Junqiang Zhu. "Effects of periodic wakes on boundary layer development on an ultra-high-lift low pressure turbine airfoil." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 231, no. 1 (2016): 25–38. http://dx.doi.org/10.1177/0957650916671421.
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The laminar-turbulent transition process in the boundary layer is of significant practical interest because the behavior of this boundary layer largely determines the overall efficiency of a low pressure turbine. This article presents complementary experimental and computational studies of the boundary layer development on an ultra-high-lift low pressure turbine airfoil under periodically unsteady incoming flow conditions. Particular emphasis is placed on the influence of the periodic wake on the laminar-turbulent transition process on the blade suction surface. The measurements were distinctive in that a closely spaced array of hot-film sensors allowed a very detailed examination of the suction surface boundary layer behavior. Measurements were made in a low-speed linear cascade facility at a freestream turbulence intensity level of 1.5%, a reduced frequency of 1.28, a flow coefficient of 0.70, and Reynolds numbers of 50,000 and 100,000, based on the cascade inlet velocity and the airfoil axial chord length. Experimental data were supplemented with numerical predictions from a commercially available Computational Fluid Dynamics code. The wake had a significant influence on the boundary layer of the ultra-high-lift low pressure turbine blade. Both the wake’s high turbulence and the negative jet behavior of the wake dominated the interaction between the unsteady wake and the separated boundary layer on the suction surface of the ultra-high-lift low pressure turbine airfoil. The upstream unsteady wake segments convecting through the blade passage behaved as a negative jet, with the highest turbulence occurring above the suction surface around the wake center. Transition of the unsteady boundary layer on the blade suction surface was initiated by the wake turbulence. The incoming wakes promoted transition onset upstream, which led to a periodic suppression of the separation bubble. The loss reduction was a compromise between the positive effect of the separation reduction and the negative effect of the larger turbulent-wetted area after reattachment due to the earlier boundary layer transition caused by the unsteady wakes. It appeared that the successful application of ultra-high-lift low pressure turbine blades required additional loss reduction mechanisms other than “simple” wake-blade interaction.
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Michelassi, V. "Shock-boundary layer interaction and transition modelling in turbomachinery flows." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 211, no. 3 (1997): 225–34. http://dx.doi.org/10.1243/0957650971537132.
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The transonic turbulent compressible flow in channels and turbine linear cascades is computed by using a Navier-Stokes solver. Turbulence effects are simulated by means of the k-ω turbulence model. A realiability constraint is introduced to improve the turbulence model performances and stability in the presence of stagnation points. In both the flow over the bump and the turbine blade, the shock induces a flow separation that affects the boundary layer development. In both cases the proposed model succeeds in predicting the flow separation. For the flow over the turbine blade a simple transition model based on integral parameters is introduced to mimic the effect of the boundary layer transition across the shock wave on the suction side. Relaminarization is also properly predicted on the pressure side, thereby allowing a good description of the boundary layer development and shock pattern.
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Solís-Gallego, Irene, Katia María Argüelles Díaz, Jesús Manuel Fernández Oro, and Sandra Velarde-Suárez. "Wall-Resolved LES Modeling of a Wind Turbine Airfoil at Different Angles of Attack." Journal of Marine Science and Engineering 8, no. 3 (2020): 212. http://dx.doi.org/10.3390/jmse8030212.
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Noise has arisen as one of the main restrictions for the deployment of wind turbines in urban environments or in sensitive ecosystems like oceans for offshore and coastal applications. An LES model, adequately planned and resolved, is useful to describe the noise generation mechanisms in wind turbine airfoils. In this work, a wall-resolved LES model of the turbulent flow around a typical wind turbine airfoil is presented and described in detail. The numerical results obtained have been validated with hot wire measurements in a wind tunnel. The description of the boundary layer over the airfoil provides an insight into the main noise generation mechanism, which is known to be the scattering of the vortical disturbances in the boundary layer into acoustic waves at the airfoil trailing edge. In the present case, 2D wave instabilities are observed in both suction and pressure sides, but these perturbations are diffused into a turbulent boundary layer prior to the airfoil trailing edge, so tonal noise components are not expected in the far-field noise propagation. The results obtained can be used as input data for the prediction of noise propagation to the far-field using a hybrid aeroacoustic model.
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Schulte, V., and H. P. Hodson. "Unsteady Wake-Induced Boundary Layer Transition in High Lift LP Turbines." Journal of Turbomachinery 120, no. 1 (1998): 28–35. http://dx.doi.org/10.1115/1.2841384.
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The development of the unsteady suction side boundary layer of a highly loaded LP turbine blade has been investigated in a rectilinear cascade experiment. Upstream rotor wakes were simulated with a moving-bar wake generator. A variety of cases with different wake-passing frequencies, different wake strength, and different Reynolds numbers were tested. Boundary layer surveys have been obtained with a single hotwire probe. Wall shear stress has been investigated with surface-mounted hot-film gages. Losses have been measured. The suction surface boundary layer development of a modern highly loaded LP turbine blade is shown to be dominated by effects associated with unsteady wake-passing. Whereas without wakes the boundary layer features a large separation bubble at a typical cruise Reynolds number, the bubble was largely suppressed if subjected to unsteady wake-passing at a typical frequency and wake strength. Transitional patches and becalmed regions, induced by the wake, dominated the boundary layer development. The becalmed regions inhibited transition and separation and are shown to reduce the loss of the wake-affected boundary layer. An optimum wake-passing frequency exists at cruise Reynolds numbers. For a selected wake-passing frequency and wake strength, the profile loss is almost independent of Reynolds number. This demonstrates a potential to design highly loaded LP turbine profiles without suffering large losses at low Reynolds numbers.
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Addison, J. S., and H. P. Hodson. "Unsteady Transition in an Axial-Flow Turbine: Part 1—Measurements on the Turbine Rotor." Journal of Turbomachinery 112, no. 2 (1990): 206–14. http://dx.doi.org/10.1115/1.2927634.
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Previously published measurements in a low-speed, single-stage, axial-flow turbine have been reanalyzed in the light of more recent understanding. The measurements include time-resolved hot-wire traverses and surface hot film gage measurements at the midspan of the rotor suction surface with three different rotor-stator spacings. Part 1 investigates the suction surface boundary layer transition process, using surface-distance time plots and boundary layer cross sections to demonstrate the unsteady and two-dimensional nature of the process. Part 2 of the paper will describe the results of supporting experiments carried out in a linear cascade together with a simple transition model, which explains the features seen in the turbine.
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Mee, D. J., N. C. Baines, and M. L. G. Oldfield. "Detailed Boundary Layer Measurements on a Transonic Turbine Cascade." Journal of Turbomachinery 114, no. 1 (1992): 163–72. http://dx.doi.org/10.1115/1.2927980.
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The boundary layers of a transonic turbine blade have been measured in detail. The full velocity profiles have been measured at a number of stations on both the suction and pressure surfaces, at conditions representative of engine operation, using a Pilot traverse technique and a large-scale (300 mm chord) linear cascade. This information has made it possible to follow the development of the boundary layers, initially laminar, through a region of natural transition to a fully developed turbulent layer. Comparisons with other, less detailed, measurements on the same profile using Pilot traverse and surface-mounted thin films confirm the essential features of the boundary layers.
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Anderson, O. L. "Calculation of Three-Dimensional Boundary Layers on Rotating Turbine Blades." Journal of Fluids Engineering 109, no. 1 (1987): 41–49. http://dx.doi.org/10.1115/1.3242613.
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An assessment has been made of the applicability of a three-dimensional boundary-layer analysis to the calculation of heat transfer and streamline flow patterns on the surfaces of both stationary and rotating turbine passages. In support of this effort, an analysis has been developed to calculate a general nonorthogonal surface coordinate system for arbitrary three-dimensional surfaces and also to calculate the boundary-layer edge conditions for compressible flow using the surface Euler equations and experimental pressure distributions. Using available experimental data to calibrate the method, calculations are presented for the endwall, and suction surfaces of a stationary cascade and for the pressure surface of a rotating turbine blade. The results strongly indicate that the three-dimensional boundary-layer analysis can give good predictions of the flow field and heat transfer on the pressure, suction, and endwall surfaces in a gas turbine passage.
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Hourmouziadis, J., F. Buckl, and P. Bergmann. "The Development of the Profile Boundary Layer in a Turbine Environment." Journal of Turbomachinery 109, no. 2 (1987): 286–95. http://dx.doi.org/10.1115/1.3262101.
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Cascade testing tries to simulate the actual flow conditions encountered in a turbine. However, it is possible to reproduce neither the free-stream turbulence structure of the turbomachinery, nor the periodic wake effects of upstream blade rows. The usual understanding is that the latter in particular results in a significantly different behavior of the boundary layer in the engine. Experimental results from cascades and turbine rigs are presented. Grid-generated free-stream turbulence structure is compared to that in the turbine. Measurements of the profile pressure distribution, flush-mounted hot films, and flow visualization were used for the interpretation of the test results. Some observations of the boundary layer development in the cascade, on the guide vanes, and on rotor blades with typically skewed boundary layers are shown indicating essentially similar behavior in all cases.
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West, Jacob R., and Sanjiva K. Lele. "Wind Turbine Performance in Very Large Wind Farms: Betz Analysis Revisited." Energies 13, no. 5 (2020): 1078. http://dx.doi.org/10.3390/en13051078.
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The theoretical limit for wind turbine performance, the so-called Betz limit, arises from an inviscid, irrotational analysis of the streamtube around an actuator disk. In a wind farm in the atmospheric boundary layer, the physics are considerably more complex, encompassing shear, turbulent transport, and wakes from other turbines. In this study, the mean flow streamtube around a wind turbine in a wind farm is investigated with large eddy simulations of a periodic array of actuator disks in half-channel flow at a range of turbine thrust coefficients. Momentum and mean kinetic energy budgets are presented, connecting the energy budget for an individual turbine to the wind farm performance as a whole. It is noted that boundary layer turbulence plays a key role in wake recovery and energy conversion when considering the entire wind farm. The wind farm power coefficient is maximized when the work done by Reynolds stress on the periphery of the streamtube is maximized, although some mean kinetic energy is also dissipated into turbulence. This results in an optimal value of thrust coefficient lower than the traditional Betz result. The simulation results are used to evaluate Nishino’s model of infinite wind farms, and design trade-offs described by it are presented.
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Cheng, Shyuan, Mahmoud Elgendi, Fanghan Lu, and Leonardo P. Chamorro. "On the Wind Turbine Wake and Forest Terrain Interaction." Energies 14, no. 21 (2021): 7204. http://dx.doi.org/10.3390/en14217204.
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Future wind power developments may be located in complex topographic and harsh environments; forests are one type of complex terrain that offers untapped potential for wind energy. A detailed analysis of the unsteady interaction between wind turbines and the distinct boundary layers from those terrains is necessary to ensure optimized design, operation, and life span of wind turbines and wind farms. Here, laboratory experiments were carried to explore the interaction between the wake of a horizontal-axis model wind turbine and the boundary layer flow over forest-like canopies and the modulation of forest density in the turbulent exchange. The case of the turbine in a canonical boundary layer is included for selected comparison. The experiments were performed in a wind tunnel fully covered with tree models of height H/zhub≈0.36, where zhub is the turbine hub height, which were placed in a staggered pattern sharing streamwise and transverse spacing of Δx/dc=1.3 and 2.7, where dc is the mean crown diameter of the trees. Particle image velocimetry is used to characterize the incoming flow and three fields of view in the turbine wake within x/dT∈(2,7) and covering the vertical extent of the wake. The results show a significant modulation of the forest-like canopies on the wake statistics relative to a case without forest canopies. Forest density did not induce dominant effects on the bulk features of the wake; however, a faster flow recovery, particularly in the intermediate wake, occurred with the case with less dense forest. Decomposition of the kinematic shear stress using a hyperbolic hole in the quadrant analysis reveals a substantial effect sufficiently away from the canopy top with sweep-dominated events that differentiate from ejection-dominated observed in canonical boundary layers. The comparatively high background turbulence induced by the forest reduced the modulation of the rotor in the wake; the quadrant fraction distribution in the intermediate wake exhibited similar features of the associated incoming flow.
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Doorly, D. J. "Modeling the Unsteady Flow in a Turbine Rotor Passage." Journal of Turbomachinery 110, no. 1 (1988): 27–37. http://dx.doi.org/10.1115/1.3262164.
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The effects of the wakes shed by an upstream blade row in forcing the transition of an otherwise laminar rotor blade boundary layer are well recognized. Previous experiments have demonstrated that the forced transition of the laminar boundary layer may greatly influence the surface heat flux. The effect of the wakes on the surface heat flux when the undisturbed boundary layer is already turbulent have been studied using an experimental simulation technique. The results have been analyzed with a view to establishing how well the effects of the wakes can be described by a model which treats only their turbulence content. The effects of wake passing at a reduced Reynolds number are also reported.
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Lynch, Stephen. "Three-Dimensional Boundary Layer in a Turbine Blade Passage." Journal of Propulsion and Power 33, no. 4 (2017): 954–63. http://dx.doi.org/10.2514/1.b36232.
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Dumitrescu, Horia, and Vladimir Cardos. "Three-dimensional turbulent boundary layer on wind turbine blades." PAMM 8, no. 1 (2008): 10611–12. http://dx.doi.org/10.1002/pamm.200810611.
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Wittwer, Adrián Roberto, Rodrigo Dorado, Gervásio Annes Degrazia, Acir Mércio Loredo-Souza, and Bardo Ernst Josef Bodmann. "ESCOAMENTO NA ESTEIRA DE TURBINAS EÓLICAS: ANÁLISE ESPECTRAL DA TURBULÊNCIA MEDIANTE TESTES EM TÚNEL DE VENTO." Ciência e Natura 38 (July 20, 2016): 46. http://dx.doi.org/10.5902/2179460x19850.
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The interaction between the incident wind and wind turbines in a wind farm causes mean velocity deficit and increased levels of turbulence in the wake. The turbulent flow is characterized by the superposition of the wind turbine wakes. In this work, the technique of turbulence spectral evaluation to reduce scale models in a boundary layer wind tunnel is presented, and different measurements of velocity fluctuations are analyzed. The results allow evaluating the spectrum configuration at different frequency ranges and the differences of the spectral behavior between the incident wind and the turbine wake flow.
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Nielson, Jordan, and Kiran Bhaganagar. "Using field data–based large eddy simulation to understand role of atmospheric stability on energy production of wind turbines." Wind Engineering 43, no. 6 (2019): 625–38. http://dx.doi.org/10.1177/0309524x18824540.
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A novel and a robust high-fidelity numerical methodology has been developed to realistically estimate the net energy production of full-scale horizontal axis wind turbines in a convective atmospheric boundary layer, for both isolated and multiple wind turbine arrays by accounting for the wake effects between them. Large eddy simulation has been used to understand the role of atmospheric stability in net energy production (annual energy production) of full-scale horizontal axis wind turbines placed in the convective atmospheric boundary layer. The simulations are performed during the convective conditions corresponding to the National Renewable Energy Laboratory field campaign of July 2015. A mathematical framework was developed to incorporate the field-based measurements as boundary conditions for the large eddy simulation by averaging the surface flux over multiple diurnal cycles. The objective of the study is to quantify the role of surface flux in the calculation of energy production for an isolated, two and three wind turbine configuration. The study compares the mean value, +1 standard deviation, and −1 standard deviation from the measured surface flux to demonstrate the role of surface heat flux. The uniqueness of the study is that power deficits from large eddy simulation were used to determine wake losses and obtain a net energy production that accounts for the wake losses. The frequency of stability events, from field measurements, is input into the calculation of an ensemble energy production prediction with wake losses for different wind turbine arrays. The increased surface heat flux increases the atmospheric turbulence into the wind turbines. Higher turbulence results in faster wake recovery by a factor of two. The faster wake recovery rates result in lowering the power deficits from 46% to 28% for the two-turbine array. The difference in net energy production between the +1 and −1 standard deviation (with respect to surface heat flux) simulations was 10% for the two-turbine array and 8% for the three-turbine array. An ensemble net energy production by accounting for the wake losses indicated the overestimation of annual energy production from current practices could be corrected by accounting for variation of surface flux from the mean value.
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Stieger, R. D., and H. P. Hodson. "The Transition Mechanism of Highly Loaded Low-Pressure Turbine Blades." Journal of Turbomachinery 126, no. 4 (2004): 536–43. http://dx.doi.org/10.1115/1.1773850.
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A detailed experimental investigation was conducted into the interaction of a convected wake and a separation bubble on the rear suction surface of a highly loaded low-pressure (LP) turbine blade. Boundary layer measurements, made with 2D LDA, revealed a new transition mechanism resulting from this interaction. Prior to the arrival of the wake, the boundary layer profiles in the separation region are inflexional. The perturbation of the separated shear layer caused by the convecting wake causes an inviscid Kelvin-Helmholtz rollup of the shear layer. This results in the breakdown of the laminar shear layer and a rapid wake-induced transition in the separated shear layer.
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Önder, Asim, and Johan Meyers. "On the interaction of very-large-scale motions in a neutral atmospheric boundary layer with a row of wind turbines." Journal of Fluid Mechanics 841 (March 1, 2018): 1040–72. http://dx.doi.org/10.1017/jfm.2018.86.
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Recent experiments have revealed the existence of very long streamwise features, denoted as very-large-scale motions (VLSMs), in the thermally neutral atmospheric boundary layer (ABL) (Hutchins et al., Boundary-Layer Meteorol., vol. 145(2), 2012, pp. 273–306). The aim of our study is to elaborate the role of these large-scale anisotropic patterns in wind-energy harvesting with special emphasis on the organization of turbulent fields around wind turbines. To this end, we perform large-eddy simulation (LES) of a turbine row operating under neutral conditions. The ABL data are produced separately in a very long domain of $240\unicode[STIX]{x1D6FF}$, where $\unicode[STIX]{x1D6FF}$ is the ABL thickness, to ensure a realistic representation for very large scales of $O(10\unicode[STIX]{x1D6FF})$. VLSMs are extracted from the LES database using a cutoff at streamwise wavelength $\unicode[STIX]{x1D706}_{x}=5\unicode[STIX]{x1D6FF}$, or $\unicode[STIX]{x1D706}_{x}=50D$ in terms of turbine diameter. Reynolds averaging of low-pass filtered fields shows that the interaction of VLSMs and turbines produce very-long-wavelength motions in the wake region, which contain approximately $20\,\%$ of the resolved Reynolds shear stress, and $30\,\%$ of the resolved streamwise kinetic energy in the shear layers. To further elucidate these statistics, we conduct a geometrical analysis using conditional averaging based on large-scale low- and high-velocity events. The conditional eddies provide evidence for very long (${\sim}10\unicode[STIX]{x1D6FF}$) and wide (${\sim}\unicode[STIX]{x1D6FF}$) streak–roller structures around the turbine row. Although all of these eddies share the same streak–roller topology, there are remarkable modifications in the morphology of the conditional eddies whose cores are located sideways to the turbines. In these cases, the turbine row pushes the whole low- or high-momentum streak aside, and prevails as a sharp boundary to the low–high-momentum streak pair. In this process, accompanying rollers remain relatively unaffected. This creates a two-way flux towards the turbine row. These observations provide some insights about the high lateral spreading observed in the large-scale Reynolds stress fields.
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Schulte, V., and H. P. Hodson. "Prediction of the Becalmed Region for LP Turbine Profile Design." Journal of Turbomachinery 120, no. 4 (1998): 839–46. http://dx.doi.org/10.1115/1.2841797.
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Recent attention has focused on the so-called “becalmed region” that is observed inside the boundary layers of turbomachinery blading and is associated with the process of wake-induced transition. Significant reductions of profile loss have been shown for high lift LP turbine blades at low Reynolds numbers due the effects of the becalmed region on the diffusing flow at the rear of the suction surface. In this paper the nature and the significance of the becalmed region are examined using experimental observations and computational studies. It is shown that the becalmed region may be modeled using the unsteady laminar boundary layer equations. Therefore, it is predictable independent of the transition or turbulence models employed. The effect of the becalmed region on the transition process is modeled using a spot-based intermittency transition model. An unsteady differential boundary layer code was used to simulate a deterministic experiment involving an isolated turbulent spot numerically. The predictability of the becalmed region means that the rate of entropy production can be calculated in that region. It is found to be of the order of that in a laminar boundary layer. It is for this reason and because the becalmed region may be encroached upon by pursuing turbulent flows that for attached boundary layers, wake-induced transition cannot significantly reduce the profile loss. However, the becalmed region is less prone to separation than a conventional laminar boundary layer. Therefore, the becalmed region may be exploited in order to prevent boundary layer separation and the increase in loss that this entails. It is shown that it should now be possible to design efficient high lift LP turbine blades.
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Pucher, P., and R. Go¨hl. "Experimental Investigation of Boundary Layer Separation With Heated Thin-Film Sensors." Journal of Turbomachinery 109, no. 2 (1987): 303–9. http://dx.doi.org/10.1115/1.3262103.
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The heated thin-film method was adapted to meet the requirements of investigations on boundary layer behavior in a turbine rig. Special multisensor probes of vaporized nickel on a polyimide foil were developed and applied to the vanes. Basic experiments with an airfoil in a free stream were carried out and a reliable interpretation of the thin-film results was found by comparison with pressure distribution, flow visualization, and laser measurements. It can be shown that this measuring device is a suitable method for the investigation of separation bubbles and boundary layer transition.
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LI, S. C., S. H. LIU, and Y. L. WU. "A NEW TYPE OF CAVITATION DAMAGE TRIGGERED BY BOUNDARY-LAYER TURBULENT PRODUCTION." Modern Physics Letters B 21, no. 20 (2007): 1285–96. http://dx.doi.org/10.1142/s0217984907013456.
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A new type of cavitation damage has been observed on the turbines installed at the Three Gorges Power Station despite no cavitation detected during model tests. Metallurgical and fluid dynamic analysis suggests that this cavitation is triggered by boundary-layer turbulent production; the damaged (roughened) spot in turn triggers subsequent cavitation (damage) immediately down stream. This forms a sustainable dynamic process, resulting in long and equal-width streamwise damage-strips with spanwise regularity reflecting the spanwise stochastic characteristics of turbulent production. Owing to the heat effect of cavitation, intergranular corrosion takes place through sensitization process, leaving the damaged surface with a corrosion appearance. Also, bluing presents at the damaged tails, owing to the nature of low-intensity damage. Extremely large turbines are much more susceptible to this type of cavitation (damage) owing to the similarity laws currently employed for turbine development not concerning the freestream turbulence and the boundary-layer dynamics.
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Bastankhah, Majid, Nicholas Hamilton, and Raúl Bayoán Cal. "Wind tunnel research, dynamics, and scaling for wind energy." Journal of Renewable and Sustainable Energy 14, no. 6 (2022): 060402. http://dx.doi.org/10.1063/5.0133993.
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The interaction of wind turbines with turbulent atmospheric boundary layer (ABL) flows represents a complex multi-scale problem that spans several orders of magnitudes of spatial and temporal scales. These scales range from the interactions of large wind farms with the ABL (on the order of tens of kilometers) to the small length scale of the wind turbine blade boundary layer (order of a millimeter). Detailed studies of multi-scale wind energy aerodynamics are timely and vital to maximize the efficiency of current and future wind energy projects, be they onshore, bottom-fixed offshore, or floating offshore. Among different research modalities, wind tunnel experiments have been at the forefront of research efforts in the wind energy community over the last few decades. They provide valuable insight about the aerodynamics of wind turbines and wind farms, which are important in relation to optimized performance of these machines. The major advantage of wind tunnel research is that wind turbines can be experimentally studied under fully controlled and repeatable conditions allowing for systematic research on the wind turbine interactions that extract energy from the incoming atmospheric flow. Detailed experimental data collected in the wind tunnel are also invaluable for validating and calibrating numerical models.
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Flaszynski, Pawel, Piotr Doerffer, and Michal Piotrowicz. "Effect of Jet Vortex Generators on Shock Wave Induced Separation on Gas Turbine Profile." Journal of Thermal Science 30, no. 4 (2021): 1435–43. http://dx.doi.org/10.1007/s11630-021-1472-x.
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AbstractThe interaction between a shock wave and a boundary layer on a suction side of gas turbine profile, namely Transition Location Effect on Shock Wave Boundary Layer Interaction, was one of main objectives of TFAST project. A generic test section in a transonic wind tunnel was designed to carry out such investigations. The design criteria were to reproduce flow conditions on the profile in wind tunnel as the one existing on the suction side of the turbine guide vane. In this paper, the effect of film cooling and jet vortex generators on the shock wave boundary layer interaction and shock induced separation is presented. Numerical results for Explicit Algebraic Reynolds Stress Model with transition modeling are compared with experimental data.
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Liu, Hongrui, Jun Liu, Qiang Du, Guang Liu, and Pei Wang. "Unsteady flow mechanism of the integrated aggressive inter-turbine duct in low Reynolds number condition." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 234, no. 9 (2020): 1507–17. http://dx.doi.org/10.1177/0954410020914786.
Full textAbstract:
Aggressive inter-turbine duct, which has ultra-high bypass ratio and ultra-short axial length, is widely applied in the modern turbofan engine because it can reduce engine weight and improve low-pressure rotor dynamic characteristics. However, the aggressive inter-turbine duct that has swirling flow, wake, shock, and tip clearance leakage flow of upstream high-pressure turbine, and even has structs in its flow channel, is liable to separate, especially in high-altitude low Reynolds number (Re) condition. In addition, its downstream low-pressure turbine is on the edge of separation too. In this paper, an integrated aggressive inter-turbine duct embedded with wide-chord low-pressure turbine nozzle is adopted to eliminate the aggressive inter-turbine duct's end-wall separation. Since there are many studies on suppressing the blade suction surface's separation by upstream wake, in this study inherent wake is utilized to suppress the boundary layer separation on low-pressure turbine nozzle's suction surface in the integrated aggressive inter-turbine duct. The paper studies the unsteady flow mechanisms of the integrated aggressive inter-turbine duct (especially the separation and transition mechanisms of low-pressure turbine nozzle's suction surface boundary layer) by the computatioinal simulation method.
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Bons, Jeffrey P., Rolf Sondergaard, and Richard B. Rivir. "The Fluid Dynamics of LPT Blade Separation Control Using Pulsed Jets." Journal of Turbomachinery 124, no. 1 (2001): 77–85. http://dx.doi.org/10.1115/1.1425392.
Full textAbstract:
The effects of pulsed vortex generator jets on a naturally separating low-pressure turbine boundary layer have been investigated experimentally. Blade Reynolds numbers in the linear turbine cascade match those for high-altitude aircraft engines and industrial turbine engines with elevated turbine inlet temperatures. The vortex generator jets (30 deg pitch and 90 deg skew angle) are pulsed over a wide range of frequency at constant amplitude and selected duty cycles. The resulting wake loss coefficient versus pulsing frequency data add to previously presented work by the authors documenting the loss dependency on amplitude and duty cycle. As in the previous studies, vortex generator jets are shown to be highly effective in controlling laminar boundary layer separation. This is found to be true at dimensionless forcing frequencies F+ well below unity and with low (10 percent) duty cycles. This unexpected low-frequency effectiveness is due to the relatively long relaxation time of the boundary layer as it resumes its separated state. Extensive phase-locked velocity measurements taken in the blade wake at an F+ of 0.01 with 50 percent duty cycle (a condition at which the flow is essentially quasi-steady) document the ejection of bound vorticity associated with a low-momentum fluid packet at the beginning of each jet pulse. Once this initial fluid event has swept down the suction surface of the blade, a reduced wake signature indicates the presence of an attached boundary layer until just after the jet termination. The boundary layer subsequently relaxes back to its naturally separated state. This relaxation occurs on a timescale which is five to six times longer than the original attachment due to the starting vortex. Phase-locked boundary layer measurements taken at various stations along the blade chord illustrate this slow relaxation phenomenon. This behavior suggests that some economy of jet flow may be possible by optimizing the pulse duty cycle and frequency for a particular application. At higher pulsing frequencies, for which the flow is fully dynamic, the boundary layer is dominated by periodic shedding and separation bubble migration, never recovering its fully separated (uncontrolled) state.