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1
Lim, Joon W., Chee Tung, and Yung H. Yu. "Prediction of Blade-Vortex Interaction Airloads With Higher-Harmonic Pitch Controls Using the 2GCHAS Comprehensive Code." Journal of Pressure Vessel Technology 123, no. 4 (June 19, 2001): 469–74. http://dx.doi.org/10.1115/1.1401025.
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Analytically predicted results of blade-vortex interaction (BVI) airloads, using the second- generation comprehensive helicopter analysis system (2GCHAS), are presented with the experimental results obtained from the higher-harmonic-control aeroacoustic rotor test (HART) program using a 40-percent, Mach-scaled model of the hingeless BO-105 main rotor. Correlations include airloads, blade tip deflections, and tip vortex geometry. The effects on blade airload predictions are studied with higher-harmonic pitch controls (HHC). It was concluded that the blade torsional deflection and the wake system play a very important role in predicting BVI airloads.
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Su, Taoyong, Yang Lu, Jinchao Ma, and Shujun Guan. "Electrically Controlled Rotor Blade Vortex Interaction Airloads and Noise Analysis Using Viscous Vortex Particle Method." Shock and Vibration 2019 (November 6, 2019): 1–15. http://dx.doi.org/10.1155/2019/9678970.
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An electrically controlled rotor (ECR), also called a swashplateless rotor, replaces a swashplate with a trailing-edge flap system to implement primary rotor control. To investigate the aerodynamic characteristics of an ECR in blade-vortex interaction (BVI) condition, an analysis model based on the viscous vortex particle method, ECR blade pitch equation, and the Weissinger-L lifting surface model is established. In this model, the ECR wake flow field vorticity is discretized as multiple vortex particles, and the vorticity-velocity form of the Navier-Stokes equation is solved to simulate the transport diffusion of the vorticity. The flap motion-inducing blade-pitch movement is obtained by solving the ECR blade-pitch movement equation via the Runge–Kutta fourth-order method. On the basis, BVI noise radiation of an ECR is evaluated using the Ffowcs Williams and Hawkings (FW-H) equation. Based on the present prediction model, the aerodynamic and acoustic characteristics of a sample ECR in BVI condition are analyzed. The results show that since the BVI event of the ECR on the advancing side is mainly caused by the interaction between the flap tip vortex and the blade, the blade spanwise range of ECR BVI occurrence on the advancing side is smaller than that of the conventional rotor. In addition, the magnitude of the maximum sound pressure level on the advancing side as well as on the retreating side of the ECR is also different from that of the conventional rotor, which is consistent with the difference in the airloads between the ECR and conventional rotor. Furthermore, a study was performed to examine the effect of the pre-index angle on the BVI-induced airloads and noise. The amplitude of the impulsive airloads of the ECR on the advancing side is increased with the increase in pre-index angle, while the amplitude of the impulsive airloads of the ECR on the retreating side is decreased. Indeed, when the pre-index angle of the sample ECR is 8 degrees, the retreating-side noise radiation lobe is almost disappeared. In addition, the different intensity of wake vorticity is the main reason for the differences of the BVI-induced airloads and noise among the ECR with different pre-index angles.
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Park, J. S., and S. N. Jung. "Comprehensive multibody dynamics analysis for rotor aeromechanics predictions in descending flight." Aeronautical Journal 116, no. 1177 (March 2012): 229–49. http://dx.doi.org/10.1017/s0001924000006813.
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AbstractThis paper studies the rotor aeromechanics in descending flight using a nonlinear flexible multibody dynamic analysis code, DYMORE. A freewake model is included in DYMORE to improve the rotor wake modelling. The wind-tunnel test data of the Higher-harmonic Aeroacoustics Rotor Test (HART) II rotor, with and without higher harmonic pitch control (HHC), and the flight test data of the full-scale utility helicopter rotor in descent are used for the aeromechanics correlation at an advance ratio of 0·15. The blade-vortex interaction (BVI) airloads are reasonably predicted for both the HART II and utility helicopter rotors, although some BVI peaks are missed on the advancing sides for both the rotors. The flap deflections and elastic torsion deformations at the blade tip are fairly correlated against the measured data of the HART II rotor. The correlation of blade structural moments for both HART II and utility helicopter rotors are not as good as the lift predictions; however, a reasonable prediction is obtained for the utility helicopter rotor.
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Park, Jae-Sang, and Young Jung Kee. "Rotor aeromechanics study using two different blade property data sets." Aircraft Engineering and Aerospace Technology 88, no. 6 (October 3, 2016): 873–84. http://dx.doi.org/10.1108/aeat-03-2015-0086.
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Purpose This paper aims to compare the comprehensive rotorcraft analyses using the two different blade section property data sets for the blade natural frequencies, airloads, elastic deformations, the trimmed rotor pitch control angles and the blade structural loads of a small-scale model rotor in a blade vortex interaction (BVI) phenomenon. Design/methodology/approach The two different blade section property data sets for the first Higher-harmonic control Aeroacoustic Rotor Test (HART-I) are considered for the present rotor aeromechanics analyses. One is the blade property data set using the predicted values which is one of the estimated data sets used for the previous validation works. The other data set uses the measured values for an uninstrumented blade. A comprehensive rotorcraft analysis code, CAMRAD II (comprehensive analytical model of rotorcraft aerodynamics and dynamics II), is used to predict the rotor aeromechanics such as the blade natural frequencies, airloads, elastic deformations, the trimmed rotor pitch control angles and the blade structural loads for the three test cases with and without higher-harmonic control pitch inputs. In CAMRAD II modelling with the two different blade property data sets, the blade is represented as a geometrically nonlinear elastic beam, and the multiple-trailer wake with consolidation model is used to consider more elaborately the BVI effect in low-speed descending flight. The aeromechanics analysis result sets using the two different blade section property data sets are compared with each other as well as are correlated with the wind-tunnel test data. Findings The predicted blade natural frequencies using the two different blade section property data sets at non-rotating condition are quite similar to each other except for the natural frequency in the fourth flap mode. However, the natural frequencies using the predicted blade properties at nominal rotating condition are lower than those with the measured blade properties except for the second lead-lag frequency. The trimmed collective pitch control angle with the predicted blade properties is higher than both the wind-tunnel test data and the result using the measured blade properties in all the three test cases. The two different blade property data sets both give reasonable predictions on the blade section normal forces with BVI in the three test cases, and the two analysis results are reasonably similar to each other. The blade elastic deformations at the tip using the measured blade properties are correlated more closely with the wind-tunnel test data than those using the predicted blade properties in most correlation examples. In addition, the predictions of blade structural loads can be slightly or moderately improved by using the measured blade properties particularly for the oscillatory flap bending moments. Finally, the movement of the sectional centre of gravity location of the uninstrumented blade has a moderate influence on the blade elastic twist at the tip in the baseline case and the oscillatory flap bending moment in the minimum noise case. Practical implications The present comparison study on rotor aeromechanics analyses using the two different blade property data sets will show the influence of blade section properties on rotor aeromechanics analysis. Originality/value This paper is the first attempt to compare the aeromechanics analysis results using the two different blade section property data sets for all three test cases (baseline, minimum noise and minimum vibration) of HART-I in low-speed descending flight.
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Bernardini, Giovanni, Jacopo Serafini, Sandro Lanniello, and Massimo Gennaretti. "Assessment of Computational Models for the Effect of Aeroelasticity on BVI Noise Prediction." International Journal of Aeroacoustics 6, no. 3 (September 2007): 199–222. http://dx.doi.org/10.1260/147547207782419570.
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This paper deals with the computational analysis of acoustic fields generated by helicopter rotors when Blade-Vortex Interactions (BVI) occur. The prediction procedure starts from the determination of the steady periodic blade deformations. Then, the BVI-affected, unsteady aerodynamics solution is obtained by a potential-flow boundary integral formulation suited for aeronautical configurations experiencing blade-wake impingements. It is applicable to blades with arbitrary shape and motion and evaluates both wake distortion and blade pressure field. Finally, the noise field radiated by the rotor is computed through an aeroacoustic tool based on the Ffowcs Williams and Hawkings equation. The numerical investigation examines the sensitivity of BVI noise prediction on the aeroelastic model applied for the calculation of blade deformations, and assesses the accuracy of the results through correlation with experimental data concerning a helicopter main rotor in descent flight. Noise predicted is examined in terms of both acoustic pressure signatures and noise radiation characteristics.
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Świrydczuk, Jerzy. "Wake-blade interaction in steam turbine stages." Polish Maritime Research 20, no. 2 (April 1, 2013): 30–40. http://dx.doi.org/10.2478/pomr-2013-0014.
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Abstract The article discusses the phenomenon of stator Wake/Rotor cascade (W/R) interaction in a steam turbine stage, and the ability to capture it in turbine stage design calculations making use of standard numerical codes. Firstly, the W/R interaction is analysed by comparing its real, experimentally recorded course with the numerical results obtained using vortex theory models and methods. This part of the analysis ends with formulating a conclusion about stochastic nature of the W/R interaction and indicating its reason, which is the vortex structure of the stator wake. Next, a question is discussed whether and how this stochastic nature of the examined phenomenon can be taken into account in calculations of Reynolds Averaged Navier-Stokes (RANS) equations. Differences are indicated between the uniform pattern of the stator wake obtained using a RANS code and the vortex structure of the real wake. It is concluded, however, that despite these differences the RANS results correctly reflect the time-averaged course of the real W/R interaction, and the process of averaging the flow parameters on the sliding plane between stator and rotor calculation areas can be treated as sort of “numerical averaging” of different realisations of the W/R interaction.
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McNerney, G. M., C. P. van Dam, and D. T. Yen-Nakafuji. "Blade-Wake Interaction Noise for Turbines With Downwind Rotors." Journal of Solar Energy Engineering 125, no. 4 (November 1, 2003): 497–505. http://dx.doi.org/10.1115/1.1627830.
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The interaction between the rotor and the tower wake is an important source of noise for wind turbines with downwind rotors. The tower wake modifies the dynamic pressure and the local flow incidence angle as seen by the blades and, hence, modifies the aerodynamic loading of the blade during blade passage. The resulting n per revolution fluctuation in the blade loading (where n is the number of blades) is the source of low frequency but potentially high amplitude sound levels. The Wind Turbine Company (WTC) Proof of Concept 250 kW (POC) wind turbine has been observed by field personnel to produce low-frequency emissions at the National Wind Technology Center (NWTC) site during specific atmospheric conditions. Consequently, WTC is conducting a three-phase program to characterize the low frequency emissions of its two-bladed wind turbines and to develop noise mitigation techniques if needed. This paper summarizes the first phase of this program including recent low-frequency noise measurements conducted on the WTC POC250 kW wind turbine, a review of the wake characteristics of circular towers as they pertain to the blade-wake interaction problem, and techniques to attenuate the sound pressure levels caused by the blade-wake interaction.
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Arndt, N. "Blade Row Interaction in a Multistage Low-Pressure Turbine." Journal of Turbomachinery 115, no. 1 (January 1, 1993): 137–46. http://dx.doi.org/10.1115/1.2929198.
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The objective of this work was to enhance the understanding of unsteady flow phenomena in multistage low-pressure turbines. For this purpose, hot-film probe measurements were made downstream of every rotor blade row of a five-stage low-pressure turbine. Rotor–rotor interaction and stator–rotor interaction were observed to have a profound influence on the flow through the low-pressure turbine. Interaction of rotors of different turbine stages occurred owing to the influence of the wakes shed by one rotor blade row upon the flow through the next downstream rotor blade row. This wake-induced rotor–rotor interaction resulted in strongly amplitude-modulated periodic and turbulent velocity fluctuations downstream of every rotor blade row with the exception of the most upstream one. Significantly different wake depths and turbulence levels measured downstream of every rotor blade row at different circumferential positions evidenced the effect of the circumferentially nonuniform stator exit flow upon the next downstream rotor blade row. Stator-rotor interaction also strongly influenced the overturning and the under-turning of the rotor wakes, caused by the rotor secondary flows, in the rotor endwall regions. Low rotor wake overturning and underturning, i.e., reduced rotor secondary flow influence, were observed to correlate well with low rotor wake turbulence levels.
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Mauffrey, Y., G. Rahier, and J. Prieur. "Numerical Investigation on Blade/Wake-Interaction Noise Generation." Journal of Aircraft 46, no. 5 (September 2009): 1479–86. http://dx.doi.org/10.2514/1.32390.
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Brooks, Thomas F., and Casey L. Burley. "Blade Wake Interaction Noise for a Main Rotor." Journal of the American Helicopter Society 49, no. 1 (January 1, 2004): 11–27. http://dx.doi.org/10.4050/jahs.49.11.
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Kousen, Kenneth A., and Joseph M. Verdon. "Active control of wake/blade-row interaction noise." AIAA Journal 32, no. 10 (October 1994): 1953–60. http://dx.doi.org/10.2514/3.12238.
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Mook, Dean T., and Bonian Dong. "Perspective: Numerical Simulations of Wakes and Blade-Vortex Interaction." Journal of Fluids Engineering 116, no. 1 (March 1, 1994): 5–21. http://dx.doi.org/10.1115/1.2910242.
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A method for simulating incompressible flows past airfoils and their wakes is described. Vorticity panels are used to represent the body, and vortex blobs (vortex points with their singularities removed) are used to represent the wake. The procedure can be applied to the simulation of completely attached flow past an oscillating airfoil. The rate at which vorticity is shed from the trailing edge of the airfoil into the wake is determined by simultaneously requiring the pressure along the upper and lower surface streamlines to approach the same value at the trailing edge and the circulation around both the airfoil and its wake to remain constant. The motion of the airfoil is discretized, and a vortex is shed from the trailing edge at each time step. The vortices are convected at the local velocity of fluid particles, a procedure that renders the pressure continuous in an inviscid fluid. When the vortices in the wake begin to separate they are split into more vortices, and when they begin to collect they are combined. The numerical simulation reveals that the wake, which is originally smooth, eventually coils, or wraps, around itself, primarily under the influence of the velocity it induces on itself, and forms regions of relatively concentrated vorticity. Although discrete vortices are used to represent the wake, the spatial density of the vortices is so high that the computed velocity profiles across a typical region of concentrated vorticity are quite smooth. Although the computed wake evolves in an entirely inviscid model of the flowfield, these profiles appear to have a viscous core. The computed spacing between the regions of concentrated vorticity in the wake and the circulations around them are in good agreement with the experimental results. As an application, a simulation of the interaction between vorticity in the oncoming stream and a stationary airfoil is also discussed.
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BOWLES, R. G. A., and F. T. SMITH. "Lifting multi-blade flows with interaction." Journal of Fluid Mechanics 415 (July 25, 2000): 203–26. http://dx.doi.org/10.1017/s0022112000008673.
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Planar flow past multiple successive blades and wakes is studied for nearly aligned configurations with normal non-symmetry inducing lift. The typical blade lies relatively near the centreline of the oncoming wake from the preceding blade. The central motion over a wide parameter range is in condensed periodic boundary layers and wakes with fixed displacement, buried within surrounding incident shear flow. This is accompanied, however, by streamwise jumps in the pressure, velocity and mass flux, across the leading edge of each blade, a new and surprising feature which is supported by the combination of incident shears and a solid surface and which is related to the normal flow through the multi-blade system. The leading-edge jumps are required in order to satisfy the equi-pressure condition at the trailing edge. Computational results include separating flows and show the lift and drag, and these are followed by a short-blade analysis which captures the main flow properties explicitly. The results agree qualitatively with experiments and direct simulations for rotor blade flows. The jump feature also extends for example to a single blade immersed in the relatively large wake of an upstream blade.
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Mori, Masaaki. "Wake-body interaction Noise Simulations by Coupling CFD and BEM." INTER-NOISE and NOISE-CON Congress and Conference Proceedings 263, no. 1 (August 1, 2021): 5360–71. http://dx.doi.org/10.3397/in-2021-3067.
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In many engineering applications, the wake-body interaction or body-vortex interaction (BVI) occurs. In the wake-body interaction, vortices shed from an upstream obstacle interact with downstream obstacle and generate noise, for example blades in a turbomachinery, tubes in a heat exchanger, rotating blades like a helicopter and wind turbine and so on. The rod-airfoil and airfoil-airfoil configurations are typical models for the wake-body interaction. A rod and an airfoil are immersed upstream of the airfoil. In this paper, we reviewed the noise mechanism generated by the wake-body interaction and show the numerical results obtained by the coupling method using commercial CFD and acoustic BEM codes. The results shows that depending on the spacing between the rod or airfoil and the airfoil, the flow patterns and noise radiation vary. With small spacing, the vortex shedding from the upstream obstacle is suppressed and it results in the suppression of the sound generation. With large spacing, the shear layer or the vortices shed from the upstream obstacle impinge on the downstream obstacle and it results in the large sound generation. The dominant peak frequency of the generated sound varies with increasing of the spacing between the two obstacles.
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Schlienger, J., A. I. Kalfas, and R. S. Abhari. "Vortex-Wake-Blade Interaction in a Shrouded Axial Turbine." Journal of Turbomachinery 127, no. 4 (February 21, 2005): 699–707. http://dx.doi.org/10.1115/1.1934263.
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This paper presents time-resolved flow field measurements at the exit of the first rotor blade row of a two stage shrouded axial turbine. The observed unsteady interaction mechanism between the secondary flow vortices, the rotor wake and the adjacent blading at the exit plane of the first turbine stage is of prime interest and analyzed in detail. The results indicate that the unsteady secondary flows are primarily dominated by the rotor hub passage vortex and the shed secondary flow field from the upstream stator blade row. The analysis of the results revealed a roll-up mechanism of the rotor wake layer into the rotor indigenous passage vortex close to the hub endwall. This interesting mechanism is described in a flow schematic within this paper. In a second measurement campaign the first stator blade row is clocked by half a blade pitch relative to the second stator in order to shift the relative position of both stator indigenous secondary flow fields. The comparison of the time-resolved data for both clocking cases showed a surprising result. The steady flow profiles for both cases are nearly identical. The analysis of the probe pressure signal indicates a high level of unsteadiness that is due to the periodic occurrence of the shed first stator secondary flow field.
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Myers, Stacey, and Sanford Fleeter. "Dipole Active Control of Wake-Blade Row Interaction Noise." Journal of Propulsion and Power 15, no. 1 (January 1999): 31–37. http://dx.doi.org/10.2514/2.5414.
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Wei, Zuojun, Ming Ni, Xiaohua Gan, Weijie Chen, and Pingping Chen. "Generation of unsteady incoming wakes for wake/blade interaction." Aerospace Science and Technology 106 (November 2020): 106127. http://dx.doi.org/10.1016/j.ast.2020.106127.
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Li, Zhi Chuan, Qi Hu Sheng, Liang Zhang, Zhi Ming Cong, and Jin Jiang. "Numerical Simulation of Blade-Wake Interaction of Vertical Axis Tidal Turbine." Advanced Materials Research 346 (September 2011): 318–23. http://dx.doi.org/10.4028/www.scientific.net/amr.346.318.
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To study the blade-wake interaction of vertical axis tidal turbine (VATT)，particles were placed in the flow field to trace blade wake during numerical simulation. Numerical simulations were conducted utilizing Euler-Lagrange model. In the simulations, the continuous phase was solved by Reynolds-averaged Navier-Stocks(RANS) equation combined with SST turbulence model and the particle trajectories of the dispersed phase were determined by momentum equation. Numerical results of predicting instantaneous blade forces and blade wakes showed good agreement with the test data. The model was also compared with previous classic free vortex model (V-DART), vortex method combined with finite element analysis (FEVDTM) and 2-D vortex panel model (VPM2D). It showed that the present model was much better than the former.
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Hodson, H. P. "An Inviscid Blade-to-Blade Prediction of a Wake-Generated Unsteady Flow." Journal of Engineering for Gas Turbines and Power 107, no. 2 (April 1, 1985): 337–43. http://dx.doi.org/10.1115/1.3239725.
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This paper describes a time-marching calculation of the unsteady flow generated by the interaction of upstream wakes with a moving blade row. The inviscid equations of motion are solved using a finite volume technique. Wake dissipation is modeled using an artificial viscosity. Predictions are presented for the rotor mid-span section of an axial turbine. Reasonable agreement is found between the predicted and measured unsteady blade surface static pressures and velocities. These and other results confirm that simple theories can be used to explain the phenomena of rotor-stator wake interactions.
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Walker, G. J., J. D. Hughes, I. Ko¨hler, and W. J. Solomon. "The Influence of Wake–Wake Interactions on Loss Fluctuations of a Downstream Axial Compressor Blade Row." Journal of Turbomachinery 120, no. 4 (October 1, 1998): 695–704. http://dx.doi.org/10.1115/1.2841780.
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The interaction between wakes of an adjacent rotor–stator or stator–rotor blade row pair in an axial turbomachine is known to produce regular spatial variations in both the time-mean and unsteady flow fields in a frame relative to the upstream member of the pair. This paper examines the influence of such changes in the free-stream disturbance field on the viscous losses of a following blade row. Hot-wire measurements are carried out downstream of the outlet stator in a 1.5-stage axial compressor having equal blade numbers in the inlet guide vane (IGV) and stator rows. Clocking of the IGV row is used to vary the disturbance field experienced by the stator blades; the influence on stator wake properties is evaluated. The magnitude of periodic fluctuations in ensemble-averaged stator wake thickness is significantly influenced by IGV wake-rotor wake interaction effects. The changes in time-mean stator losses appear marginal.
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Sentker, A., and W. Riess. "Experimental investigation of turbulent wake–blade interaction in axial compressors." International Journal of Heat and Fluid Flow 21, no. 3 (June 2000): 285–90. http://dx.doi.org/10.1016/s0142-727x(00)00011-4.
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Ashworth, D. A., J. E. LaGraff, and D. L. Schultz. "Unsteady Interaction Effects on a Transitional Turbine Blade Boundary Layer." Journal of Turbomachinery 111, no. 2 (April 1, 1989): 162–68. http://dx.doi.org/10.1115/1.3262251.
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Results are presented illustrating the detailed behavior of the suction surface boundary layer of a transonic gas turbine rotor in a two-dimensional cascade under the influence of both free-stream turbulence and simulated nozzle guide vane wakes and shocks. The instrumentation included thin film resistance thermometers along with electrical analogues of the one-dimensional heat conduction equations to obtain wide bandwidth heat transfer rate measurements in a short duration wind tunnel. This instrumentation provides sufficient time resolution to track individual wake and shock-related events and also the turbulent bursts of a transitional boundary layer. Wide bandwidth surface pressure transducers and spark Schlieren photography were used in support of these heat transfer measurements. The results showed a direct relationship between the passage of wake disturbances and transient surface heat transfer enhancements. It was possible to track both wake and transitional events along the surface and to compare these with the expected convection rates. Analysis of the signals allowed direct calculations of intermittency factors, which compared well with predictions. Additional effects due to a moving shock/boundary layer interaction were investigated. These resulted in marked variations in heat transfer rate both above and below the laminar values. These excursions were associated with separation and re-attachment phenomena.
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Stella, A., G. Guj, F. Di Felice, and M. Elefante. "Experimental Investigation of Propeller Wake Evolution by Means of LDV and Flow Visualizations." Journal of Ship Research 44, no. 03 (September 1, 2000): 155–69. http://dx.doi.org/10.5957/jsr.2000.44.3.155.
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An experimental investigation of the propeller wake has been performed in a cavitation tunnel using LDV and flow visualizations. The objective is the hydrodynamic and geometrical characterization of the wake flow field and its downstream evolution features. Implications of the physical aspects for wake modeling are also highlighted. The viscous blade wake, originating in the boundary layer on the blade surfaces, the trailing vortex sheets, due to the radial gradient of the bound circulation, as well as the turbulence distribution are identified at the trailing edge and followed. The near-wake geometry is quantitatively determined describing the progressive bending of the blade wake sheets, the slipstream contraction and the tip vortex trajectory. Furthermore, the effects of turbulent diffusion and viscous dissipation, which cause a rapid space-broadening of the velocity gradients in the trailing-edge wake, are examined. Insights into the viscous interaction between blade flow and roll-up process in the tip region are also proposed. Finally, the onset and development of the slipstream instability leading to the breakdown of the vortices system in the far wake are studied also by means of visualizations in incipient cavitating flow conditions.
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Chen, Ping-Hei, and Jr-Ming Miao. "Effect of Upstream Wake on Shower-Head Film Cooling." International Journal of Rotating Machinery 2, no. 4 (1996): 269–80. http://dx.doi.org/10.1155/s1023621x96000140.
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The present study aims to investigate the effect of an upstream wake on the convective transport phenomena over a turbine blade with shower-head film cooling. A naphthalene sublimation technique was implemented to obtain the detailed mass transfer distributions on both suction and pressure surfaces of the test blade. All mass transfer runs were conducted on a blowing-type wind tunnel with a six-blade linear cascade. The leading edge of the test blade was drilled with three rows of equally spaced injection holes. The upstream wake was simulated by a circular bar with the same diameter as that of the trailing edge of the test blade.The test condition was fixed at Re = 397,000, M = 0.8, and Tu = 0.4% and upstream wakes were generated at four different locations ahead of the blade cascade. Measured results show that there is a difference in mass transfer rate from the case without upstream wake. This difference is greater on the suction side than on the pressure side. The difference results from the interaction between the wake flow that is induced by the upstream wake and the injection flows that are ejected from the multi-rows of injection holes on the test blade. It was also found that the location of upstream wake generation significantly affects the mass transfer distributions on both surfaces of test blade.
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Casciaro, Claudia, Martin Treiber, and Michael Sell. "Unsteady Transport Mechanisms in an Axial Turbine." Journal of Turbomachinery 122, no. 4 (February 1, 2000): 604–12. http://dx.doi.org/10.1115/1.1290398.
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A numerical analysis using a commercial unsteady Navier–Stokes solver has been performed on a pin/blade configuration, in order to assess the efficacy of a commercial code in calculating time-periodic interactions and to gain a better understanding of the unsteady flow physics in axial turbines. Two cases have been investigated, with the pin positioned at 25 and 50 percent of true chord ahead of the leading edge. Both configurations have been computed both two and three dimensionally. The two-dimensional case was used to examine the influence of numerical parameters, such as mesh, time, and space discretization. The three-dimensional case allowed insight into the complete flow field including the wake influence on the secondary flow and mixing processes of the blade row. The basic mechanisms of the wake–blade interaction proved, as expected, to be the same for both pin positions. Yet, as the closest pin wake interaction with the blade field was much stronger, its features have helped to identify the respective roles of wake fluid transport and blade potential field for both cases. The latter effect, noticeably strong with the thick leading edge blade form presented in this study, has often been neglected, and this study helps shed new light on this phenomenon. The code used had been validated in previous work for pin-free steady flow within the same blade row and the new time-dependent case has served to confirm the code range and limitations. [S0889-504X(00)02104-8]
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Wheeler, Andrew P. S., Robert J. Miller, and Howard P. Hodson. "The Effect of Wake Induced Structures on Compressor Boundary-Layers." Journal of Turbomachinery 129, no. 4 (July 31, 2006): 705–12. http://dx.doi.org/10.1115/1.2720499.
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The interaction of a convected wake with a compressor blade boundary layer was investigated. Measurements within a single-stage compressor were made using an endoscopic PIV system, a surface mounted pressure transducer, hotfilms and hotwire traverses, along with CFD simulations. The wake/leading-edge interaction was shown to lead to the formation of a thickened laminar boundary-layer, within which turbulent spots formed close to the leading edge. The thickened boundary-layer became turbulent and propagated down the blade surface, giving rise to pressure perturbations of 7% of the inlet dynamic head in magnitude. The results indicate that wake/leading-edge interactions have a crucial role to play in the performance of compressor blades in the presence of wakes.
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Zhu, Zhifeng. "Numerical Investigation of Viscous Flow Velocity Field around a Marine Cavitating Propeller." Advances in Mechanical Engineering 6 (January 1, 2014): 272316. http://dx.doi.org/10.1155/2014/272316.
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Velocity field around a ship cavitating propeller is investigated based on the viscous multiphase flow theory. Using a hybrid grid, the unsteady Navier-stokes (N-S) and the bubble dynamics equations are solved in this paper to predict the velocity in a propeller wake and the vapor volume fraction on the back side of propeller blade for a uniform inflow. Compared with experimental results, the numerical predictions of cavitation and axial velocity coincide with the measured data. The evolution of tip vortex is shown, and the interaction between the tip vortex of the current blade and the wake of the next one occurs in the far propeller wake. The frequency of velocity signals changes from shaft rate to blade rate. The phenomena reflect the instability of propeller wake.
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Lardeau, S., and M. A. Leschziner. "Unsteady Reynolds-Averaged Navier-Stokes Computations of Transitional Wake/Blade Interaction." AIAA Journal 42, no. 8 (August 2004): 1559–71. http://dx.doi.org/10.2514/1.4608.
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Hwang, C. J., and J. Y. Kuo. "Numerical analysis and active control of wake/blade‐row interaction noise." Journal of the Acoustical Society of America 105, no. 2 (February 1999): 1140. http://dx.doi.org/10.1121/1.425428.
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Lardeau, S., and M. A. Leschziner. "Unsteady RANS modelling of wake–blade interaction: computational requirements and limitations." Computers & Fluids 34, no. 1 (January 2005): 3–21. http://dx.doi.org/10.1016/j.compfluid.2004.04.001.
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Chow, Yi-Chih, Oguz Uzol, and Joseph Katz. "Flow Nonuniformities and Turbulent “Hot Spots” Due to Wake-Blade and Wake-Wake Interactions in a Multi-Stage Turbomachine." Journal of Turbomachinery 124, no. 4 (October 1, 2002): 553–63. http://dx.doi.org/10.1115/1.1509078.
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This experimental study provides striking examples of the complex flow and turbulence structure resulting from blade-wake and wake-wake interactions in a multi-stage turbomachine. Particle image velocimetry (PIV) measurements are performed within the entire 2nd stage of a two-stage turbomachine. The experiments are performed in a facility that allows unobstructed view of the entire flow field, facilitated using transparent rotor and stator and a fluid that has the same optical index of refraction as the blades. This paper contains data on the phase-averaged flow structure including velocity, vorticity and strain-rate, as well as the turbulent kinetic energy and shear stress, at mid span, for several orientation of the rotor relative to the stator. Two different test setups with different blade geometries are used in order to highlight and elucidate complex phenomena involved, as well as to demonstrate that some of the interactions are characteristic to turbomachines and can be found in a variety of geometries. The first part of the paper deals with the interaction of a 2nd-stage rotor with the wakes of both the rotor and the stator of the 1st stage. Even before interacting with the blade, localized regions with concentrated mean vorticity and elevated turbulence levels form at the intersection of the rotor and stator wakes of the 1st stage. These phenomena persist even after being ingested by the rotor blade of the 2nd stage. As the wake segment of the 1st-stage rotor blade arrives to the 2nd stage, the rotor blades become submerged in its elevated turbulence levels, and separate the region with negative vorticity that travels along the pressure side of the blade, from the region with positive vorticity that remains on the suction side. The 1st-stage stator wake is chopped-off by the blades. Due to difference in mean lateral velocity, the stator wake segment on the pressure side is advected faster than the segment on the suction side (in the absolute frame of reference), creating discontinuities in the stator wake trajectory. The nonuniformities in phase-averaged velocity distributions generated by the wakes of the 1st stage persist while passing through the 2nd-stage rotor. The combined effects of the 1st-stage blade rows cause 10–12 deg variations of flow angle along the pressure side of the blade. Thus, in spite of the large gap between the 1st and 2nd rotors (compared to typical rotor-stator spacings in axial compressors), 6.5 rotor axial chords, the wake-blade interactions are substantial. The second part focuses on the flow structure at the intersection of the wakes generated by a rotor and a stator located upstream of it. In both test setups the rotor wake is sheared by the nonuniformities in the axial velocity distributions, which are a direct result of the “discontinuities” in the trajectories of the stator wake. This shearing creates a kink in the trajectory of the rotor wake, a quadruple structure in the distribution of strain, regions with concentrated vorticity, high turbulence levels and high shear stresses, the latter with a complex structure that resembles the mean strain. Although the “hot spots” diffuse as they are advected downstream, they still have elevated turbulence levels compared to the local levels around them. In fact, every region of wake intersection has an elevated turbulence level.
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Ashworth, D. A., J. E. LaGraff, D. L. Schultz, and K. J. Grindrod. "Unsteady Aerodynamic and Heat Transfer Processes in a Transonic Turbine Stage." Journal of Engineering for Gas Turbines and Power 107, no. 4 (October 1, 1985): 1022–30. http://dx.doi.org/10.1115/1.3239806.
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The effect of the interaction of the wake from a nozzle guide vane with the rotor may be simulated in part by means of a stationary rotor and a moving wake system. This technique is applied to a transonic rotor blade cascade, and the unsteady measurements of surface pressure and heat transfer rate are compared with baseline data obtained without the wake interaction. The wake-rotor interaction results in a change in inlet incidence angle and this effect is also examined in the steady-state case. It is found that the shock waves from the moving wake system have a major effect on the instantaneous heat transfer rates.
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Wang, T., and F. N. Coton. "A modified near wake dynamic model for rotor analysis." Aeronautical Journal 103, no. 1021 (March 1999): 143–46. http://dx.doi.org/10.1017/s0001924000064952.
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Abstract The Beddoes near wake model, developed for high resolution blade vortex interaction computations, enables efficient numerical evaluation of the downwash due to trailed vorticity in the near wake of a helicopter rotor. The model is, however, limited by the assumption that the near wake lies in the plane of the rotor and, in some cases, by its inability to accurately evaluate the induced velocity contribution from vorticity trailed from inboard blade sections. In this paper, modifications to the method are proposed which address these issues and allow it to be used with confidence over a wider range of rotor flows.
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Vouros, Stavros, Ioannis Goulos, Calum Scullion, Devaiah Nalianda, and Vassilios Pachidis. "Impact of Tip-Vortex Modeling Uncertainty on Helicopter Rotor Blade–Vortex Interaction Noise Prediction." Journal of the American Helicopter Society 66, no. 1 (January 1, 2021): 1–13. http://dx.doi.org/10.4050/jahs.66.012005.
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Free-wake models are routinely used in aeroacoustic analysis of helicopter rotors; however, their semiempiricism is accompanied with uncertainty related to the modeling of physical wake parameters. In some cases, analysts have to resort to empirical adaption of these parameters based on previous experimental evidence. This paper investigates the impact of inherent uncertainty in wake aerodynamic modeling on the robustness of helicopter rotor aeroacoustic analysis. A free-wake aeroelastic rotor model is employed to predict high-resolution unsteady airloads, including blade–vortex interactions. A rotor aeroacoustics model, based on integral solutions of the Ffowcs Williams–Hawkings equation, is utilized to calculate aerodynamic noise in the time domain. The individual analytical models are incorporated into an uncertainty analysis numerical procedure, implemented through nonintrusive Polynomial Chaos expansion. The potential sources of uncertainty in wake tip-vortex core growth modeling are identified and their impact on noise predictions is systematically quantified. When experimental data to adjust the tip-vortex core model are not available the uncertainty in acoustic pressure and noise impact at observers dominated by blade–vortex interaction noise can reach up to 25% and 3.50 dB, respectively. A set of generalized uncertainty maps is derived, for use as modeling guidelines for aeroacoustic analysis in the absence of the robust evidence necessary for calibration of semiempirical vortex core models.
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Chen, Zi Xi, Neha Marathe, and Siva Parameswaran. "CFD Study of Wake Interaction of Two Wind Turbines." Advanced Materials Research 472-475 (February 2012): 2726–30. http://dx.doi.org/10.4028/www.scientific.net/amr.472-475.2726.
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Understanding the wake behavior properly would help in designing proper layouts of wind farms to obtain maximum power and improved turbine life. This research aims at studying the impact of power of a turbine that is in the wake of another turbine under uniform inflow condition. Computational Fluid Dynamics (CFD) simulations are carried out to represent the velocity deficit behind two turbines in-line with the wind using the Virtual Blade Model (VBM). Power loss of the second wind turbine located at different distance downstream is also calculated.
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Hodson, H. P., and W. N. Dawes. "On the Interpretation of Measured Profile Losses in Unsteady Wake–Turbine Blade Interaction Studies." Journal of Turbomachinery 120, no. 2 (April 1, 1998): 276–84. http://dx.doi.org/10.1115/1.2841403.
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The interaction of wakes shed by a moving blade row with a downstream blade row causes unsteady flow. The meaning of the free-stream stagnation pressure and stagnation enthalpy in these circumstances has been examined using simple analyses, measurements, and CFD. The unsteady flow in question arises from the behavior of the wakes as so-called negative jets. The interactions of the negative jets with the downstream blades lead to fluctuations in static pressure, which in turn generate fluctuations in the stagnation pressure and stagnation enthalpy. It is shown that the fluctuations of the stagnation quantities created by unsteady effects within the blade row are far greater than those within the incoming wake. The time-mean exit profiles of the stagnation pressure and stagnation enthalpy are affected by these large fluctuations. This phenomenon of energy separation is much more significant than the distortion of the time-mean exit profiles that is caused directly by the cross-passage transport associated with the negative jet, as described by Kerrebrock and Mikolajczak. Finally, it is shown that if only time-averaged values of loss are required across a blade row, it is nevertheless sufficient to determine the time-mean exit stagnation pressure.
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Tran, L. T., and D. B. Taulbee. "Prediction of Unsteady Rotor-Surface Pressure and Heat Transfer From Wake Passings." Journal of Turbomachinery 114, no. 4 (October 1, 1992): 807–17. http://dx.doi.org/10.1115/1.2928034.
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The research described in this paper is a numerical investigation of the effects of unsteady flow on gas turbine heat transfer, particularly on a rotor blade surface. The unsteady flow in a rotor blade passage and the unsteady heat transfer on the blade surface as a result of wake/blade interaction are modeled by the inviscid flow/boundary layer approach. The Euler equations that govern the inviscid flow are solved using a time-accurate marching scheme. The unsteady flow in the blade passage is induced by periodically moving a wake model across the passage inlet. Unsteady flow solutions in the passage provide pressure gradients and boundary conditions for the boundary-layer equations that govern the viscous flow adjacent to the blade surface. Numerical solutions of the unsteady turbulent boundary layer yield surface heat flux values that can then be compared to experimental data. Comparisons with experimental data show that unsteady heat flux on the blade suction surface is well predicted, but the predictions of unsteady heat flux on the blade pressure surface do not agree.
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El Fajri, Oumnia, Shanti Bhushan, David S. Thompson, and Tim O'Doherty. "Numerical investigation of shallow-water effects on hydrokinetic turbine wake recovery." International Marine Energy Journal 3, no. 1 (May 13, 2020): 25–35. http://dx.doi.org/10.36688/imej.3.25-35.
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Thrust, power and intermediate wake predictions obtained using resolved rotating blade with sliding mesh simulations for a hydrokinetic turbine (HKT) are assessed using the open-source flow solver OpenFOAM. Single- and two-phase URANS and DES computations are performed for three-blade, 0.5m diameter (D) turbine mounted on a stanchion that intersects the free surface with a tip-speed ratio λ = 6.15. The thrust and power predictions compare within 5% of the experimental data. Results show that the thrust predictions are dominated by the pressure distribution on the blades, whereas the shear stress plays a significant role in the power predictions. The turbine performance showed unsteadiness with amplitudes around 3% of the mean, due to the disruption of the flow each time a blade passed in front of the stanchion. The wake recovery is primarily due to the growth of shear layers (originating from the blade tips) towards the turbine axis, which are primarily caused by the cross-plane turbulent velocity. The shear layer growth is enhanced by the turbulence produced by the stanchion. Predictions of the mean wake profile compared within 10% of the experimental data, which is significant improvement over previous Fluent predictions that showed large errors of 22%. The improved predictions in OpenFOAM is attributed to better turbulence predictions. Two-phase results show that the interaction between the wake and free-surface is initiated by the interaction of stanchion with the free-surface. The free-surface creates a blockage effect that accelerates the flow in the upper bypass region and enhances the wake recovery.
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Arnone, Andrea, Michele Marconcini, Alberto Scotti Del Greco, and Ennio Spano. "Numerical Investigation of Three-Dimensional Clocking Effects in a Low Pressure Turbine." Journal of Turbomachinery 126, no. 3 (July 1, 2004): 375–84. http://dx.doi.org/10.1115/1.1740780.
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One and a half stages of a low pressure turbine were investigated using a three-dimensional time-accurate viscous solver. Unsteady analyses were carried out by varying the circumferential relative position of consecutive vanes to study the effects of clocking on performance. Assuming that efficiency improvements by clocking are linked to the wake tangential position with respect to the successive blade, a certain circumferential shift in this position can be observed along the blade height due to blade twist and nonradial stacking, giving different contributions. In order to assess this phenomenon, results from three-dimensional computations were compared with a quasi-three-dimensional analysis at mid-span. The effects of clocking on wake interaction mechanisms and unsteady blade loadings are presented and discussed.
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Fan, S., and B. Lakshminarayana. "Computation and Simulation of Wake-Generated Unsteady Pressure and Boundary Layers in Cascades: Part 1—Description of the Approach and Validation." Journal of Turbomachinery 118, no. 1 (January 1, 1996): 96–108. http://dx.doi.org/10.1115/1.2836612.
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The unsteady pressure and boundary layers on a turbomachinery blade row arising from periodic wakes due to upstream blade rows are investigated in this paper. A time-accurate Euler solver has been developed using an explicit four-stage Runge–Kutta scheme. Two-dimensional unsteady nonreflecting boundary conditions are used at the inlet and the outlet of the computational domain. The unsteady Euler solver captures the wake propagation and the resulting unsteady pressure field, which is then used as the input for a two-dimensional unsteady boundary layer procedure to predict the unsteady response of blade boundary layers. The boundary layer code includes an advanced k–ε model developed for unsteady turbulent boundary layers. The present computational procedure has been validated against analytic solutions and experimental measurements. The validation cases include unsteady inviscid flows in a flat-plate cascade and a compressor exit guide vane (EGV) cascade, unsteady turbulent boundary layer on a flat plate subject to a traveling wave, unsteady transitional boundary layer due to wake passing, and unsteady flow at the midspan section of an axial compressor stator. The present numerical procedure is both efficient and accurate in predicting the unsteady flow physics resulting from wake/blade-row interaction, including wake-induced unsteady transition of blade boundary layers.
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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 (September 29, 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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Yang, Rongfei, Guoliang Wang, Haixu Liu, Honghui Xiang, and Jie Gao. "Numerical Study on the Flow Mechanism of Compressor Rotor Blade Vibration under Different Inlet Probe Configurations." International Journal of Aerospace Engineering 2020 (December 1, 2020): 1–12. http://dx.doi.org/10.1155/2020/8897211.
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In the performance test of a compressor, the overstrain alarm of a rotor blade occurred and it was thought to be caused by a large-sized inlet probe. To explain and further avoid the occurrence of this phenomenon, the influences of probe strut configuration on the vibration strain of the compressor rotor blade and the corresponding flow mechanism are studied by using a one-way fluid-structure coupling calculation method. Firstly, the probe strut is simplified as a cylinder with a diameter of 10 mm and located upstream of the inlet stator with the strut wake impinging on the stator blade according to the compressor test. Then, the three scenarios are considered: moving the strut away from the stator blade in axial direction, shifting the strut half of the stator pitch circumferentially, and reducing the strut diameter. The analysis results show that the characteristics of blade vibration are determined by the excitation force on the rotor blade. Under the interaction between the large-sized strut and the compressor, in addition to the excitation force with the strut passing frequency, a force with a lower frequency, namely, the strut-wake-induced frequency, is also observed. The amplitude of the excitation force on the rotor blade depends on the probe configuration. When one of the excitation force frequencies is close to a natural frequency of the rotor blade, the blade resonates, and the amplitude of blade strain varies with the amplitude of the excitation force. In order to reduce the adverse effect of upstream strut wake on the compressor rotor blade vibration, the inlet probe strut should be designed with a smaller diameter and be placed further upstream of the stator in such a way that the strut wake vortex passes through the midpassage of the following stator.
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Yi, Mei, and Qu Jianjun. "Numerical Study of Flow Field and Aerodynamic Performance of Straight Bladed VAWT at Variable Tip Speed Ratios." Open Mechanical Engineering Journal 9, no. 1 (October 7, 2015): 1017–24. http://dx.doi.org/10.2174/1874155x01509011017.
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This paper studies the relationship between unsteady flow features and instantaneous torque and power performance of straight bladed vertical axis wind turbine at variable tip speed ratios. The rotor unsteady flow field simulation was carried out by using computational fluid dynamics method. The flow physics and the principle of changing flow field acting on torque performance and power performance have been analyzed where the rotating rotor was the major concern. The results show that the flow feature alters from periodical blade dynamic stall vortexes generation, development and shedding at low tip speed ratio to cyclical formation, evolution and diffusion of blade wake flow with the rising tip speed ratio. Both vortex shedding around the blade and interaction of blade wakes degrade the rotor aerodynamic performance. It is suggested that, to absorb maximum wind energy, delay the blade vortex shedding and reduce the range of blade wake, evolution and diffusion should be included in the rotor aerodynamic design.
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Glegg, Stewart A. L. "Prediction of blade wake interaction noise based on a turbulent vortex model." AIAA Journal 29, no. 10 (October 1991): 1545–51. http://dx.doi.org/10.2514/3.10774.
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Rahier, G., and Y. Delrieux. "Blade-Vortex Interaction Noise Prediction Using a Rotor Wake Roll-Up Model." Journal of Aircraft 34, no. 4 (July 1997): 522–30. http://dx.doi.org/10.2514/2.2204.
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Macumber, Daniel L., Anuradha Annaswamy, David N. Beal, and Stephen Huyer. "Noise Control Due to the Stator Wake Blade Interaction via Tail Articulation." IEEE Journal of Oceanic Engineering 32, no. 3 (July 2007): 551–64. http://dx.doi.org/10.1109/joe.2007.896830.
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Lim, Joon W., and Roger C. Strawn. "Computational Modeling of HART II Blade-Vortex Interaction Loading and Wake System." Journal of Aircraft 45, no. 3 (May 2008): 923–33. http://dx.doi.org/10.2514/1.31081.
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Dullenkopf, K., A. Schulz, and S. Wittig. "The Effect of Incident Wake Conditions on the Mean Heat Transfer of an Airfoil." Journal of Turbomachinery 113, no. 3 (July 1, 1991): 412–18. http://dx.doi.org/10.1115/1.2927890.
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The flow phenomena of wakes shed by upstream blade rows is a well-known problem in turbomachinery, which influences blade forces, vibrations, losses, and heat transfer. With respect to the heat load to turbine blades, this problem becomes even more complex because of the interaction between wake, potential flow, and the boundary layer along the surface of the airfoil. Experimentally evaluated mean heat transfer coefficients obtained under different unsteady initial conditions are reported. The heat transfer measurements have been carried out in the cascade test facility at the ITS in Karlsruhe, using a rotating bar wake generator placed upstream of the cascade to simulate the wake passing process. The variation of the wake parameters includes different wake passing frequencies, cascade inlet Reynolds numbers, and wake inclination angles. In addition, the relevant parameters of the unsteady wake have been measured by means of a fixed hot-wire anemometer using the ensemble-average technique. The results are compared to those from the literature for the wake of a cylinder in crossflow. They also serve as experimental base for parallel theoretical analyses.
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Grinderslev, Christian, Federico Belloni, Sergio González Horcas, and Niels Nørmark Sørensen. "Investigations of aerodynamic drag forces during structural blade testing using high-fidelity fluid–structure interaction." Wind Energy Science 5, no. 2 (May 5, 2020): 543–60. http://dx.doi.org/10.5194/wes-5-543-2020.
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Abstract. Aerodynamic loads need to be known for planning and defining test loads beforehand for wind turbine blades that are tested for fatigue certifications. It is known that the aerodynamic forces, especially drag, are different for tests and operation, due to the entirely different flow conditions. In test facilities, a vibrating blade will move in and out of its own wake, increasing the drag forces on the blade. This is not the case in operation. To study this special aerodynamic condition present during experimental tests, numerical simulations of a wind turbine blade during pull–release tests were conducted. High-fidelity three-dimensional computational fluid dynamics methods were used throughout the simulations. In this way, the fluid mechanisms and their impact on the moving blade are clarified, and through the coupling with a structural solver, the fluid–structure interaction is studied. Results are compared to actual measurements from experimental tests, verifying the approach. It is found that the blade experiences a high drag due to its motion towards its own whirling wake, resulting in an effective drag coefficient of approximately 5.3 for the 90∘ angle of attack. This large drag coefficient was implemented in a fatigue test load simulation, resulting in a significant decrease in bending moment along the blade, leading to less load being applied than intended. The confinement from the test facility did not impact this specific test setup, but simulations with longer blades could possibly yield different conclusions. To the knowledge of the authors, this investigation, including three-dimensional effects, structural coupling and confinement, is the first of its kind.
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Calcagno, Guido, F. Di Felice, M. Felli, and F. Pereira. "A Stereo-PIV Investigation of a Propeller's Wake behind a Ship Model in a Large Free-surface Tunnel." Marine Technology Society Journal 39, no. 2 (June 1, 2005): 94–102. http://dx.doi.org/10.4031/002533205787444051.
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An experimental investigation of a five blade MAU propeller wake behind a Series 60 Cb=0.6 ship model has been performed using Stereo Particle Image Velocimetry (Stereo-PIV) in a large free-surface cavitation tunnel. The investigation of the wake and its evolution during propeller revolution and at different longitudinal stations has pointed out the capability of Stereo-PIV in resolving the complex flow field with great accuracy. As a first step of this investigation, a systematic measurement analysis has been done to find the best angle between the two cameras. The blade viscous wake, developing from the blade surface boundary layers; the trailing vortex sheets, due to the radial gradient of the bound circulation; and the velocity fluctuation distributions are identified and discussed. The complex interaction between the hull wake and propeller is described through the evolution of the mean velocity components and the vorticity fields. In the near field the effects of turbulent diffusion and viscous dissipation, which cause a rapid space-broadening of the velocity gradients in the trailing edge wake, are also examined. Comparison with LDV measurements shows a substantial agreement between the two techniques.