Academic literature on the topic 'Streamwise velocity component'
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Journal articles on the topic "Streamwise velocity component"
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MORRISON, J. F., B. J. McKEON, W. JIANG, and A. J. SMITS. "Scaling of the streamwise velocity component in turbulent pipe flow." Journal of Fluid Mechanics 508 (June 10, 2004): 99–131. http://dx.doi.org/10.1017/s0022112004008985.
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Hellström, Leo H. O., and Alexander J. Smits. "Structure identification in pipe flow using proper orthogonal decomposition." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, no. 2089 (March 13, 2017): 20160086. http://dx.doi.org/10.1098/rsta.2016.0086.
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The energetic motions in direct numerical simulations of turbulent pipe flow at Re τ =685 are investigated using proper orthogonal decomposition. The procedure is extended such that a pressure component is identified in addition to the three-component velocity field for each mode. The pressure component of the modes is shown to align with the streamwise velocity component associated with the large-scale motions, where positive pressure coincides with positive streamwise velocity, and vice versa. The streamwise evolution of structures is then visualized using a conditional mode, which exhibit a strong similarity to the large-scale, low-momentum motions. A low-pressure region is present in the downstream section of the structure, and a high-pressure region is present in the upstream section. This article is part of the themed issue ‘Toward the development of high-fidelity models of wall turbulence at large Reynolds number’.
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Antonia, R. A., L. W. B. Browne, and D. A. Shah. "Characteristics of vorticity fluctuations in a turbulent wake." Journal of Fluid Mechanics 189 (April 1988): 349–65. http://dx.doi.org/10.1017/s0022112088001053.
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Measurements of the lateral components of the vorticity fluctuation have been made in the self-preserving turbulent wake of a circular cylinder. Each component was obtained separately using two X-wires separated in the appropriate lateral directions. The two velocity derivatives which make up the streamwise vorticity component were also determined but not simultaneously. An approximation to the streamwise vorticity was made from these measurements. Moments, probability density functions and spectra of the three vorticity components across the wake are presented and discussed. The high-wavenumber behaviour of the spectra is compared with calculations, based on local isotropy. Satisfactory agreement with the calculations is obtained for the lateral vorticity components over a significant high-wavenumber range. The approximated streamwise vorticity spectrum tends towards the isotropic calculation at very large wavenumbers.
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Nygaard, K. J., and A. Glezer. "Evolution of stream wise vortices and generation of small-scale motion in a plane mixing layer." Journal of Fluid Mechanics 231 (October 1991): 257–301. http://dx.doi.org/10.1017/s0022112091003397.
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The evolution of streamwise vortices in a plane mixing layer and their role in the generation of small-scale three-dimensional motion are studied in a closed-return water facility. Spanwise-periodic streamwise vortices are excited by a time-harmonic wavetrain with span wise-periodic amplitude variations synthesized by a mosaic of 32 surface film heaters flush-mounted on the flow partition. For a given excitation frequency, virtually any span wise wavelength synthesizable by the heating mosaic can be excited and can lead to the formation of streamwise vortices before the rollup of the primary vortices is completed. The onset of streamwise vortices is accompanied by significant distortion in the transverse distribution of the streamwise velocity component. The presence of inflexion points, absent in corresponding velocity distributions of the unforced flow, suggests the formation of locally unstable regions of large shear in which broadband perturbations already present in the base flow undergo rapid amplification, followed by breakdown to small-scale motion. Furthermore, as a result of spanwise-non-uniform excitation the cores of the primary vortices are significantly altered. The three-dimensional features of the streamwise vortices and their interaction with the base flow are inferred from surfaces of r.m.s. velocity fluctuations and an approximation to cross-stream vorticity using three-dimensional single component velocity data. The striking enhancement of small-scale motion and the spatial modification of its distribution, both induced by the streamwise vortices, can be related to the onset of the mixing transition.
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Lee, Jae Hwa, Hyung Jin Sung, and Ronald J. Adrian. "Space–time formation of very-large-scale motions in turbulent pipe flow." Journal of Fluid Mechanics 881 (October 25, 2019): 1010–47. http://dx.doi.org/10.1017/jfm.2019.786.
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We examine the origin of very-large-scale motions (VLSMs) in fully developed turbulent pipe flow at friction Reynolds number, $\mathit{Re}_{\unicode[STIX]{x1D70F}}=934$, using data from a direct numerical simulation. The VLSMs and the packet-like large-scale motions (LSMs) found in this study are very similar to those found in earlier studies. Three-dimensional time-evolving instantaneous fields show that one component of the process leading to the large streamwise length of VLSMs is the concatenation of adjacent streamwise LSMs caused by the continuous elongation of LSMs due to the strain component of the mean shear. Spatial organization patterns of the VLSMs and LSMs and their properties are studied by separating auto-correlation of the streamwise velocity fluctuations into the components of the VLSM and the LSM defined by low-pass/high-pass filtering in the streamwise direction. The structures of the two-point spatial correlations of the streamwise velocity component of the VLSMs and the LSMs in the streamwise-azimuthal plane are characterized by multiple maxima and complex patterns that beg explanation in terms of patterned coherent arrangements of the LSMs. Using proper orthogonal decomposition (POD), it is found that the X-shape correlation pattern of the VLSMs results from the superposition of very long helically inclined structures and streamwise-aligned structures. Further explanation of the patterns in the correlations of the VLSMs and LSMs is provided through the study of synthetically constructed arrangements of simple hairpin packet models of the LSM. Head-to-tail alignment of the model packets along streamwise and helical directions suggested by the eigenvalues of the POD creates a pair of long roll-cells centred above the logarithmic layer, and bracketing the LSMs. These roll-cells are pure kinematic consequences of the induction within the LSM packets, but they may also serve to organize smaller packets.
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BIRCH, DAVID M., and JONATHAN F. MORRISON. "Similarity of the streamwise velocity component in very-rough-wall channel flow." Journal of Fluid Mechanics 668 (December 3, 2010): 174–201. http://dx.doi.org/10.1017/s0022112010004647.
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The streamwise velocity component is studied in fully developed turbulent channel flow for two very rough surfaces and a smooth surface at comparable Reynolds numbers. One rough surface comprises sparse and isotropic grit with a highly non-Gaussian distribution. The other is a uniform mesh consisting of twisted rectangular elements which form a diamond pattern. The mean roughness heights (±) the standard deviation) are, respectively, about 76(±42) and 145(±150) wall units. The flow is shown to be two-dimensional and fully developed up to the fourth-order moment of velocity. The mean velocity profile over the grit surface exhibits self-similarity (in the form of a logarithmic law) within the limited range of 0.04≤y/h≤0.06, but the profile over the mesh surface does not, even though the mean velocity deficit and higher moments (up to the fourth order) all exhibit outer scaling over both surfaces. The distinction between self-similarity and outer similarity is clarified and the importance of the former is explained. The wake strength is shown to increase slightly over the grit surface but decrease over the mesh surface. The latter result is contrary to recent measurements in rough-wall boundary layers. Single- and two-point velocity correlations reveal the presence of large-scale streamwise structures with circulation in the plane orthogonal to the mean velocity. Spanwise correlation length scales are significantly larger than corresponding ones for both internal and external smooth-wall flows.
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McKeon, B. J., and J. F. Morrison. "Asymptotic scaling in turbulent pipe flow." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 365, no. 1852 (January 16, 2007): 771–87. http://dx.doi.org/10.1098/rsta.2006.1945.
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The streamwise velocity component in turbulent pipe flow is assessed to determine whether it exhibits asymptotic behaviour that is indicative of high Reynolds numbers. The asymptotic behaviour of both the mean velocity (in the form of the log law) and that of the second moment of the streamwise component of velocity in the outer and overlap regions is consistent with the development of spectral regions which indicate inertial scaling. It is shown that an ‘inertial sublayer’ in physical space may be considered as a spatial analogue of the inertial subrange in the velocity spectrum and such behaviour only appears for Reynolds numbers R + >5×10 3 , approximately, much higher than was generally thought.
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WARHOLIC, MICHAEL D., GAVIN M. SCHMIDT, and THOMAS J. HANRATTY. "The influence of a drag-reducing surfactant on a turbulent velocity field." Journal of Fluid Mechanics 388 (June 10, 1999): 1–20. http://dx.doi.org/10.1017/s0022112099004498.
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A two-component laser-Doppler velocimeter, with high spatial and temporal resolution, was used to study how the introduction of a drag-reducing surfactant to water changes the fully-developed velocity field in an enclosed rectangular channel. Measurements were made for four different Reynolds numbers, Re = 13300; 19100; 32000, and 49100 (based on the bulk viscosity, the half-height of the channel, and the viscosity of water). For a fixed volumetric flow the pressure drop was reduced by 62 to 76% when compared to a Newtonian flow with an equal wall viscosity. Measurements were made of the mean streamwise velocity, the root mean square of two components of the fluctuating velocity, the Reynolds shear stress and the spectral density function of the fluctuating velocity in the streamwise direction. The Reynolds shear stress is found to be zero over the whole channel and the spectra of the streamwise velocity fluctuations show a sharp cutoff at a critical frequency, fc. The ratio of the cutoff frequency to the root mean square of the streamwise velocity fluctuations is found to be approximately equal to 1 mm−1. The observation of a zero Reynolds shear stress indicates the existence of additional mean shear stresses (or mean transfers of momentum) that are not seen with a Newtonian fluid. Furthermore, the presence of a random fluctuating velocity field suggests a production of turbulence by a mechanism other than that usually found for a fully developed flow. Possible explanations for this behaviour are presented.
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Lee, Myoungkyu, and Robert D. Moser. "Direct numerical simulation of turbulent channel flow up to." Journal of Fluid Mechanics 774 (June 10, 2015): 395–415. http://dx.doi.org/10.1017/jfm.2015.268.
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A direct numerical simulation of incompressible channel flow at a friction Reynolds number ($\mathit{Re}_{{\it\tau}}$) of 5186 has been performed, and the flow exhibits a number of the characteristics of high-Reynolds-number wall-bounded turbulent flows. For example, a region where the mean velocity has a logarithmic variation is observed, with von Kármán constant ${\it\kappa}=0.384\pm 0.004$. There is also a logarithmic dependence of the variance of the spanwise velocity component, though not the streamwise component. A distinct separation of scales exists between the large outer-layer structures and small inner-layer structures. At intermediate distances from the wall, the one-dimensional spectrum of the streamwise velocity fluctuation in both the streamwise and spanwise directions exhibits $k^{-1}$ dependence over a short range in wavenumber $(k)$. Further, consistent with previous experimental observations, when these spectra are multiplied by $k$ (premultiplied spectra), they have a bimodal structure with local peaks located at wavenumbers on either side of the $k^{-1}$ range.
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GAYME, D. F., B. J. McKEON, A. PAPACHRISTODOULOU, B. BAMIEH, and J. C. DOYLE. "A streamwise constant model of turbulence in plane Couette flow." Journal of Fluid Mechanics 665 (October 19, 2010): 99–119. http://dx.doi.org/10.1017/s0022112010003861.
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Streamwise and quasi-streamwise elongated structures have been shown to play a significant role in turbulent shear flows. We model the mean behaviour of fully turbulent plane Couette flow using a streamwise constant projection of the Navier–Stokes equations. This results in a two-dimensional three-velocity-component (2D/3C) model. We first use a steady-state version of the model to demonstrate that its nonlinear coupling provides the mathematical mechanism that shapes the turbulent velocity profile. Simulations of the 2D/3C model under small-amplitude Gaussian forcing of the cross-stream components are compared to direct numerical simulation (DNS) data. The results indicate that a streamwise constant projection of the Navier–Stokes equations captures salient features of fully turbulent plane Couette flow at low Reynolds numbers. A systems-theoretic approach is used to demonstrate the presence of large input–output amplification through the forced 2D/3C model. It is this amplification coupled with the appropriate nonlinearity that enables the 2D/3C model to generate turbulent behaviour under the small-amplitude forcing employed in this study.
Dissertations / Theses on the topic "Streamwise velocity component"
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"The Effect of a Splitter Plate on the Flow around a Surface-Mounted Finite Circular Cylinder." Thesis, 2011. http://hdl.handle.net/10388/ETD-2011-09-171.
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Splitter plates are passive flow control devices for reducing drag and suppressing vortex shedding from bluff bodies. Most studies of splitter plates involve the flow around an “infinite” circular cylinder, however, in the present study the flow around a surface-mounted finite-height circular cylinder, with a wake-mounted splitter plate, was studied experimentally in a low-speed wind tunnel using a force balance and single-component hot-wire anemometry. Four circular cylinders of aspect ratios AR = 9, 7, 5 and 3 were tested for a Reynolds number range of Re = 1.9×10^4 to 8.2×10^4. The splitter plates had lengths, relative to the cylinder diameter, of L/D = 1, 1.5, 2, 3, 5 and 7, thicknesses ranging from T/D = 0.10 and 0.15, and were the same height as the cylinder being tested. The cylinders were partially immersed in a flat-plate turbulent boundary layer, where the range of boundary layer thickness relative to the cylinder diameter was δ/D = 1.4 to 1.5.
Measurements were made of the mean drag force coefficient, the Strouhal number at the mid-height position, and the Strouhal number and power spectra along the cylinder height. For all four finite circular cylinders, the splitter plates were effective at reducing the magnitude of the Strouhal number, and weakening or even suppressing vortex shedding, depending on the specific combination of AR and L/D. Compared to the case of an infinite circular cylinder, the splitter plate is less effective at reducing the mean drag force coefficient of a finite circular cylinder. The largest drag reduction was obtained for the cylinder of AR = 9 and splitter plates of L/D = 1 to 3, while negligible drag reduction occurred for the shorter cylinders.
Book chapters on the topic "Streamwise velocity component"
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Furbish, David Jon. "Vorticity and Fluid Strain." In Fluid Physics in Geology. Oxford University Press, 1997. http://dx.doi.org/10.1093/oso/9780195077018.003.0015.
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Many flows involve a sense of rotation. Clear examples include cyclones, whirlpools, and eddies. Less apparent, perhaps, is the interesting result that a one-dimensional shearing flow—for example, Couette flow—possesses a rotational component. As we will see below, the idea of fluid vorticity provides a way to characterize the rotational qualities of such flows. In addition, our treatment of vorticity will provide a way to distinguish between simple shear and pure shear of a fluid. Because shearing motions involve viscous dissipation of energy in real fluids, our descriptions of vorticity and shear will form an important part of the development of dynamical equations for flows that involve viscous forces (Chapter 12). The idea of vorticity also is useful in visualizing the onset of flow separation (Example Problem 11.4.2), very viscous flow behavior (Example Problem 12.6.5), and certain aspects of turbulence (Chapters 14 and 15). Beyond this, our treatment of vorticity is not emphasized. Let us envision a vorticity meter made of two small orthogonal vanes, with the end of one vane marked for easy identification. (Such meters can readily be constructed and used as described next.) Consider placing this meter at some position within a fluid that is rotating like a rigid body. The vorticity meter in this case rotates with the fluid in such a way that its orientation relative to the axis of rotation of the fluid remains fixed. As we will see below, the fluid possesses a definite vorticity that is reflected in the observation that the vorticity meter rotates with respect to its own axis. In this regard, we also may observe that the angular velocity of this local rotation of the meter is the same regardless of its distance from the fluid axis. Now consider a one-dimensional (Couette) shear flow. A vorticity meter placed at any position within this flow also rotates about its center due to the streamwise velocity differential over the span of the meter. Judging from the behavior of the meter, this flow also possesses a definite vorticity. We also may envision that the rate of rotation varies directly with the velocity gradient du/dy.
Conference papers on the topic "Streamwise velocity component"
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Findlay, Matthew J., Pingfan He, Martha Salcudean, and Ian S. Gartshore. "A Row of Streamwise-Inclined Jets in Crossflow: Measurements and Calculations." In ASME 1996 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1996. http://dx.doi.org/10.1115/96-gt-167.
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The velocity profiles and turbulence characteristics are measured for a row of square jets inclined at 30° to the streamwise direction. The jet spacing-to-width ratio is 3.0 and no temperature (density) difference between the jets and the crossflow is introduced. Measurements are made using a three-component LDV system operating in coincidence mode which provides three components of velocity and all six turbulent Reynolds stresses at each location. Jet-to-crossflow velocity ratios (blowing ratios) of 1.5. 1.0, and 0.5 are used and the jet Reynolds number is fixed at about 5000 for all velocity ratios. The results are compared with previous data from normal jets at the same blowing ratios so that the influence of inclination on vortex formation can be shown. Calculations are carried out for all cases using a non-orthogonal finite volume computer code with the k-ε turbulence model. It is shown that the flow field at the jet exit is strongly influenced by the crossflow as well as by the inlet conditions at the entrance to the jet orifice. Therefore it is very useful to extend the computational domain into the plenum. Computational results compared with experimental results for a velocity ratio of 0.5 agree reasonably well. Some under-prediction of the streamwise flow velocity is observed. The computed turbulence kinetic energy values also drop below the experimental values downstream and near the wall. Agreement is not as good for the higher velocity ratios, particularly for the turbulence kinetic energy. Strong non-isotropy of the turbulence field can be observed from the experimental data.
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Dominguez-Ontiveros, Elvis E., Carlos Estrada-Perez, and Yassin A. Hassan. "Time and Spatial Pressure and Velocity Correlation in a Microbubble Laden Boundary Layer." In ASME/JSME 2007 5th Joint Fluids Engineering Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/fedsm2007-37291.
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Measurements of the velocity fields and wall pressure have been performed in a microbubble laden boundary layer in order to have a better understanding of the degree of correlation between these two parameters. Cross-correlation coefficients have been obtained from synchronized measurements of pressure and velocity at different distances from the wall in a channel flow. The results show a high correlation between pressure and both the streamwise and normal components of the velocity vector for the two-phase flow case. In contrast, the correlation coefficient between pressure and velocity is high only for the streamwise component of the velocity vector for single phase flow (no microbubbles in the flow). A practical application of these measurements is obtaining data and information to better describe the mechanism responsible for the microbubble drag reduction phenomenon, which has great potential for energy savings on different transport means.
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Hall, Andre´ M., Mark N. Glauser, and Charles E. Tinney. "An Experimental Investigation of the Pressure-Velocity Cross-Correlation in an Axisymmetric Jet." In ASME 2005 Fluids Engineering Division Summer Meeting. ASMEDC, 2005. http://dx.doi.org/10.1115/fedsm2005-77338.
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This study investigates the strength of the pressure-velocity correlations of a Mach 0.6, axisymmetric jet, with an exit nozzle diameter of 50.8mm. Experiments are conducted at a constant exit temperature of 25°C, and exit pressure and temperature are balanced with ambient conditions. The instantaneous velocity measurements are acquired using a multi-component LDA system who’s measurement volume is traversed along several radial and streamwise locations within the potential core, and mixing layer regions of the flow. The fluctuating lip pressure is simultaneously sampled by an azimuthal array of (15) dynamic transducers, evenly spaced at 24°. These are positioned just outside the shear layer near the jet exit at z/D = 0.875, and 1.75R from the centerline, where the pressure field has been shown to be hydrodynamic. From this multi-point evaluation, the cross-correlations between the near-field pressure array (fixed), and streamwise component of the velocity field (traversed) are examined as a function of radial, streamwise, and also azimuthal separation. The results illustrate a remarkable coherence between the near field pressure and the velocity field, on the order of 25%. Streamwise convection velocities of 0.77Uj and 0.73Uj are calculated within the potential core and shear layer, respectively. Analysis of the coherency spectra illustrates the frequency band of the correlations and suggest that the potential core and mixing layer regions of the flow are, in general, governed by the high and low frequency motions of the flow, respectively. The azimuthal modal distribution of the cross-correlation shows the dominance of the column mode of the jet, with no higher modes exhibited within the potential core region, and only modes 1 & 2 within the shear layer.
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Chernoray, Valery, and Johan Hja¨rne. "Improving the Accuracy of Multihole Probe Measurements in Velocity Gradients." In ASME Turbo Expo 2008: Power for Land, Sea, and Air. ASMEDC, 2008. http://dx.doi.org/10.1115/gt2008-50492.
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This study describes an implementation and verification of an effective and reliable correction for the finite-size effects of pressure probes. A modified version of correction by Ligrani et al. (Exp. Fluids, vol. 7, 1989, p. 424) was used. It is shown that the correction procedure can be implemented in two steps as in Ligrani et al. or in a single step, either for probe pressures, or for velocity components. The latter correction method is found to have the best performance and studied in very detail. The effect of the correction in application to the highly three-dimensional flow downstream of the outlet guide vanes is scrutinized through detailed side-by-side comparison with corresponding cross hot-wire data. The influence of the correction on all three velocity components, flow streamlines and streamwise vorticity fields is thoroughly examined. Two flow cases with different incoming turbulence intensities are considered. The study demonstrates a very good efficiency and reliability of the correction, which lead to a significant improvement of the corrected velocity data. The improvement in crossflow velocity components has allowed correct description of the flow streamlines, and as a result, the secondary flow field structures were resolved more accurately. The considered correction does not affect the streamwise vorticity component, which is clarified as well. A very important fact is that the correction is not found to over-correct and distort the data, thus can be used safely. A very good performance of the correction for the finite-size effects of pressure probes presented in this study allows us to recommend it as a mandatory step in postprocessing procedures for multihole pressure probes.
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Adaramola, M. S., D. Sumner, and D. J. Bergstrom. "Turbulent Wake of a Stack and the Influence of Velocity Ratio." In ASME 2006 Pressure Vessels and Piping/ICPVT-11 Conference. ASMEDC, 2006. http://dx.doi.org/10.1115/pvp2006-icpvt-11-93629.
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The effect of the jet-to-cross-flow velocity ratio, R, on the turbulent wake of a cylindrical stack of AR = 9 was investigated with two-component thermal anemometry. The cross-flow Reynolds number was ReD = 2.3×104, the jet Reynolds number ranged from Red = 7×103 to 4.6×104, and R was varied from 0 to 3. The stack was partially immersed in a flat-plate turbulent boundary layer, with a boundary layer thickness-to-height ratio of δ/H = 0.5 at the location of the stack. The flow around the stack was broadly classified into three flow regimes depending on the value of R, which were the downwash (R < 0.5), cross-wind dominated (0.5 < R < 1.5), and jet-dominated (R > 1.5) regimes. Each flow regime had a distinct structure to the mean velocity (streamwise and wall-normal directions), turbulence intensity (streamwise and wall-normal directions), and Reynolds shear stress fields.
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Norimatsu, Ryohei, Shogo Takai, and Masaharu Matsubara. "Relation Between Disturbance of Boundary Layer and Free Stream Turbulence Component." In ASME-JSME-KSME 2011 Joint Fluids Engineering Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ajk2011-16030.
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In a flat plate boundary layer subjected to isotropic free stream turbulence of few percents turbulence intensity, the streaks, which longitudinally elongated regions of high and low streamwise velocity, appear in the boundary layer and then break down to turbulent spots. Experiments and DNS have revealed that the profile of the streamwise fluctuation energy has a peak at the middle of boundary layer and that the disturbance grows in proportion to the streamwise distance from the leading edge. These results were in good agreement with the non-modal theory. Though the theory suggested that in lower free stream turbulent case modal disturbance has chance to develop and breakdown to turbulence, experimental investigations have not clarified the maximum intensity of the free stream turbulence at which the modal disturbance triggers transition. It is know that there are other processes of the boundary transition that start with a short streak breakdown. In this study various types of the free stream turbulence including anisotropic turbulence are scrutinized using turbulence grids and their relation to the disturbance growth in the boundary layer is investigated. The result with hot-wire measurements shows that the spanwise spectra of the free stream turbulence are essential factor for the non-modal growth. This would be a major step for developing prediction method of boundary layer transition.
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Duriez, Thomas, Jean-Luc Aider, and Jose Eduardo Wesfreid. "Base Flow Modification by Streamwise Vortices: Application to the Control of Separated Flows." In ASME 2006 2nd Joint U.S.-European Fluids Engineering Summer Meeting Collocated With the 14th International Conference on Nuclear Engineering. ASMEDC, 2006. http://dx.doi.org/10.1115/fedsm2006-98541.
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We first demonstrate the potential of cylindrical vortex generators to control the separation over a smoothly curved ramp in a low velocity hydrodynamic channel. We then focus on the influence of a row of four cylindrical vortex generators on a spatially growing flat plate boundary layer. Using two-component PIV measurements, we show how the boundary layer is modulated by counter-rotating streamwise vortices. We also analyze the 3D velocity field using non-linear perturbations to emphasize a clear modification of the base flow. This base flow modification, together with spanwise modulation, can explain the delay of the separation of the boundary layer over the curved ramp.
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Fang, J., P. R. McHugh, and H. M. Atassi. "Distortion of Three-Dimensional Vorticity Waves by a Cascade of Airfoils." In ASME 1989 International Gas Turbine and Aeroengine Congress and Exposition. American Society of Mechanical Engineers, 1989. http://dx.doi.org/10.1115/89-gt-246.
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The evolution of three-dimensional vorticity waves impinging on a cascade of loaded blades in subsonic flow is studied. Analytical expressions are derived for the streamwise, normal and spanwise components of the vorticity and the associated rotational velocity. These unsteady flow quantities are calculated, and their variations analyzed and plotted for a typical loaded cascade. The results show that at large distances from the blades a slow but long range distortion of the incoming vorticity waves takes place. Near the blade surface, the stretching and turning of the vorticity produce large values for the streamwise vorticity component.
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Oshkai, P., T. Yan, A. Velikorodny, and S. VanCaeseele. "Acoustic Power Calculation in Deep Cavity Flows: A Semi-Empirical Approach." In ASME 2007 Pressure Vessels and Piping Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/pvp2007-26404.
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Acoustic power generated by turbulent flow over a coaxial side branch (deep cavity) resonator mounted in a rectangular duct is calculated using a semi-empirical approach. Instantaneous flow velocity is decomposed into an irrotational acoustic component and vorticity-bearing hydrodynamic field. The total velocity at several phases of the acoustic oscillation cycle is measured using digital particle image velocimetry. The acoustic velocity field is calculated numerically. The emphasis is on the effect of the accurate geometry representation for the acoustic field modeling on the calculated acoustic power. Despite the generally low levels of acoustic radiation from the coaxial side branches, when the main duct is incorporated into the model for calculation of the acoustic velocity, the acoustic velocity exhibits substantial horizontal (streamwise) components in the vicinity of the cavity corners. This streamwise acoustic velocity correlates with hydrodynamic horizontal velocity fluctuations, thus contributing to the calculated acoustic power. In addition, spatial structure and strength of the acoustic source changes as the distance between the side branches varies. The transformation of the acoustic source structure is characterized in terms of patterns of instantaneous and phase-averaged flow velocity, vorticity, and streamline topology.
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Hobson, G. V., T. M. Caruso, and J. R. Carlson. "Three-Component LDV Measurements in the Wake of a Compressor Cascade With Flow Separation." In ASME Turbo Expo 2003, collocated with the 2003 International Joint Power Generation Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/gt2003-38980.
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Measurements were taken of the vortex system and turbulent flow that resulted from the interaction between a stator blade and the approaching end-wall boundary layer in a linear cascade of compressor blades. Data were taken at a Reynolds number based on blade chord of and 640000. Five-hole pressure measurements were conducted upstream and downstream of the blade row. The approaching boundary layer was also characterized with the laser-Doppler velocimeter. Downstream three-component laser-Doppler velocimetry surveys were conducted at three streamwise stations to map the location and velocity characteristics of the wake and vortex system. Results clearly showed the extent of the vortex emanating from the separation of the boundary layer on the suction side of the blade. Finally all components of mean flow velocity and turbulence are documented for the last survey station. These data will form challenging test case for numerical code validation.