scholarly journals A Study of Reynolds Stresses and Loss Generation at the Inlet to a Centrifugal Vaneless Diffuser

1995 ◽  
Author(s):  
Ali Pinarbasi ◽  
Mark W. Johnson
Keyword(s):  
Boundary Layer ◽  
Significant Contribution ◽  
Shear Layers ◽  
Secondary Flows ◽  
Reynolds Stresses ◽  
Vaneless Diffuser ◽  
Flow Measurements ◽  
Passage Vortex ◽  
The Mean ◽  
Turbulence Production

Detailed flow measurements at the inlet to a centrifugal compressor vaneless diffuser are presented. The mean velocities and six component stress tensor are used to determine the turbulence production terms which lead to total pressure loss. Four regions in the flow are identified as potential sources of loss — the blade wake, the shear layers between passage wake and jet, the thickened hub boundary layer and the interaction region between the secondary flow within the blade wake and the passage vortex. The blade wakes generate most turbulence, with smaller contributions from the hub boundary layer and secondary flows, but no significant contribution is apparent from the passage wake shear layers.

Stress Tensor Measurements within the Vaneless Diffuser of a Centrifugal Compressor

1989 ◽  
Vol 203 (1) ◽  
pp. 51-59 ◽  
Author(s):  
T M A Maksoud ◽  
M W Johnson
Keyword(s):  
Centrifugal Compressor ◽  
Sampling Technique ◽  
Phase Lock Loop ◽  
Tangential Component ◽  
Secondary Flows ◽  
Axial Component ◽  
Reynolds Stresses ◽  
Vaneless Diffuser ◽  
Cross Sectional ◽  
Impeller Outlet

Distributions of normal and shear (Reynolds) stresses inside the vaneless diffuser of a low-speed centrifugal compressor are presented. The measurements were made using a triple hot-wire system and a phase lock loop sampling technique. Results were obtained on cross-sectional planes at eight radial stations between the impeller outlet and the diffuser exit at three different flowrates. The turbulence was highly anisotropic and became more so as the flowrate was increased. The tangential component of turbulent intensity was found to be significantly smaller than either the radial or axial component. The blade wake observed at the diffuser inlet decays very rapidly due to the strong tangential Reynolds stresses generated by the opposed secondary flows on either side of the wake. The passage wake decays very much more slowly and is still identifiable at the diffuser discharge.

scholarly journals Study of Mean- and Turbulent-Velocity Fields in a Large-Scale Turbine-Vane Passage

1980 ◽  
Vol 102 (1) ◽  
pp. 88-95 ◽  
Author(s):  
D. A. Bailey
Keyword(s):  
Boundary Layer ◽  
Laser Doppler Velocimetry ◽  
Large Scale ◽  
Guide Vane ◽  
Velocity Fields ◽  
Inlet Guide Vane ◽  
Test Conditions ◽  
Passage Vortex ◽  
Turbine Vane ◽  
The Mean

Laser-Doppler velocimetry was used to investigate the secondary flow in the endwall region of a large-scale turbine inlet-guide-vane passage. The mean and turbulent velocities were measured for three different test conditions. The different test conditions consisted of variations in the blade aspect ratio and the inlet boundary-layer thickness or all three cases, a passage vortex was identified and its development documented. The turbulent stresses within the vortex were found to be quite low in comparison with the turbulence in the inlet boundary layer.

M. J. Hartmann Memorial Session Paper: Turbulence Characteristics in a Supersonic Cascade Wake Flow

1994 ◽  
Vol 116 (4) ◽  
pp. 586-596 ◽  
Author(s):  
P. L. Andrew ◽  
Wing-fai Ng
Keyword(s):  
Boundary Layer ◽  
Incidence Angle ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Shear Stresses ◽  
State University ◽  
Mean Flow ◽  
Flow Measurements ◽  
The Mean ◽  
Supersonic Wake

The turbulent character of the supersonic wake of a linear cascade of fan airfoils has been studied using a two-component laser-doppler anemometer. The cascade was tested in the Virginia Polytechnic Institute and State University intermittent wind tunnel facility, where the Mach and Reynolds numbers were 2.36 and 4.8 × 106, respectively. In addition to mean flow measurements, Reynolds normal and shear stresses were measured as functions of cascade incidence angle and streamwise locations spanning the near-wake and the far-wake. The extremities of profiles of both the mean and turbulent wake properties´ were found to be strongly influenced by upstream shock-boundary -layer interactions, the strength of which varied with cascade incidence. In contrast, the peak levels of turbulence properties within the shear layer were found to be largely independent of incidence, and could be characterized in terms of the streamwise position only. The velocity defect turbulence level was found to be 23 percent, and the generally accepted value of the turbulence structural coefficient of 0.30 was found to be valid for this flow. The degree of similarity of the mean flow wake profiles was established, and those profiles demonstrating the most similarity were found to approach a state of equilibrium between the mean and turbulent properties. In general, this wake flow may be described as a classical free shear flow, upon which the influence of upstream shock-boundary-layer interactions has been superimposed.

Secondary Losses in a Large Deflection Annular Turbine Cascade: Effect of the Entry Boundary Layer Thickness

1986 ◽  
Author(s):  
M. Govardhan ◽  
N. Venkatrayulu ◽  
D. Prithvi Raj
Keyword(s):  
Boundary Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Impulse Turbine ◽  
Flow Measurements ◽  
Local Loss ◽  
Trailing Edges ◽  
Annular Cascade

The paper presents the results of three dimensional flow measurements behind the trailing edges of an impulse turbine blade row of 120° deflection in an annular cascade. The entry boundary layer thickness was systematically varied on the hub and casing walls separately and its effect on secondary flows and losses is investigated. With the increase of entry boundary layer thickness, it has been found that (i) the contours of local loss coefficient show that the magnitude of the hub loss core increased, (ii) the loss cores near the hub and casing wall are convected away from the walls, (iii) the spanwise variation of the pitchwise averaged losses indicate that the position of large loss peak near the hub wall remains the same, but the magnitude of the loss increases, (iv) the exit static pressure increases and the exit velocity in general decreases, (v) the degree of underturning of flow increases and (vi) the net secondary losses do not change appreciably.

Off-Design Flow Measurements in a Centrifugal Compressor Vaneless Diffuser

1995 ◽  
Vol 117 (4) ◽  
pp. 602-608 ◽  
Author(s):  
A. Pinarbasi ◽  
M. W. Johnson
Keyword(s):  
Flow Rate ◽  
Centrifugal Compressor ◽  
Secondary Flows ◽  
Design Flow ◽  
Vaneless Diffuser ◽  
Flow Measurements ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Flow Rates ◽  
Study Results

Detailed measurements have been taken of the three-dimensional velocity field within the vaneless diffuser of a backswept low speed centrifugal compressor using hot-wire anemometry. A 16 percent below and an 11 percent above design flow rate were used in the present study. Results at both flow rates show how the blade wake mixes out more rapidly than the passage wake. Strong secondary flows inherited from the impeller at the higher flow rate delay the mixing out of the circumferential velocity variations, but at both flow rates these circumferential variations are negligible at the last measurement station. The measured tangential/radial flow angle is used to recommend optimum values for the vaneless space and vane angle for design of a vaned diffuser.

Effects of Simplified Platform Overlap and Cavity Geometry on the Endwall Flow: Measurements and Computations in a Low-Speed Linear Turbine Cascade

2013 ◽  
Author(s):  
G. D. MacIsaac ◽  
S. A. Sjolander ◽  
T. J. Praisner ◽  
E. A. Grover ◽  
R. Jurek
Keyword(s):  
Recirculation Zone ◽  
Secondary Flows ◽  
Pressure Probe ◽  
Computational Domain ◽  
Turbine Cascade ◽  
Streamwise Vorticity ◽  
Flow Measurements ◽  
Passage Vortex ◽  
Flow Features ◽  
Cfd Analyses

Incorporating the platform overlap and endwall cavity into the early stages of turbine CFD analyses is desirable from the perspective of accurately capturing the near endwall flow features. However, the overlap and cavity geometry increase the complexity of the computational domain making CFD meshes more difficult to generate and the CFD solutions more resource intensive. Thus, geometric approximations are often made to simplify the CFD analysis. This paper examines, experimentally, the secondary flows of a linear turbine cascade with three different platform overlap geometries, two of which incorporate geometric simplifications. These are then compared with the corresponding computations. Experimental measurements were collected using a seven-hole pressure probe at a plane located 40% of the axial chord downstream of the trailing edge. Steady-state computational predictions were performed using ANSYS CFX 12.0 and employed the SST transition turbulence model. The experimental results show that the presence of an upstream rim-seal creates a stronger passage vortex, relative to a flat endwall, resulting in larger integrated losses as well as higher levels of secondary kinetic energy and streamwise vorticity. Subtle differences in the strength of the passage vortex and the associated losses are observed for the simplified geometries in both the measured and predicted results. By examining the details of the cavity flow, a recirculation zone is identified which energizes the formation of the passage vortex. The effect of the recirculation zone may be attenuated or intensified by the rim-seal geometry. The paper concludes by addressing the validity and usefulness of the proposed platform overlap simplifications in design-oriented computations.

Loss Mechanism of Low-Pressure Turbine Secondary Flows Due to Different Incoming Boundary Layers

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
Jiangdong Hou ◽  
Chao Zhou
Keyword(s):  
Boundary Layer ◽  
Stokes Equations ◽  
Vortex Pair ◽  
Low Pressure ◽  
Secondary Flows ◽  
Dominant Factor ◽  
Loss Mechanism ◽  
Turbulent Dissipation ◽  
Low Pressure Turbine ◽  
The Mean

Abstract In high bypass ratio engines, the flow exits the interturbine duct (ITD) and enters the low-pressure (LP) turbine. This paper aims to understand the effects of the boundary layer at the exit of ITD on the endwall secondary flows and loss of the first blade row in a low-pressure turbine. From the Navier–Stokes equations, the loss is decomposed into the parts generated by the mean vortex as well as turbulence theoretically. The result of computational fluid dynamics (CFD) shows that the incoming boundary layer from the ITD increases the total pressure loss coefficient by 14% compared to the case with uniform inlet condition. Although the distribution of the secondary vortices is strongly affected by the inlet boundary layer, the loss generated by the mean vortex within the blade passage is hardly affected. The analysis based on the turbulent dissipation shows that the dominant factor leading to the loss increase is the turbulent dissipation downstream of the blade trailing edge (TE) near the hub. The mixing process of the wake and the strong counter-rotating vortex pair (CVP) increases the turbulent dissipation significantly. It is also found that a simplified incoming boundary layer defined by the Prandtl's one-seventh power law can not reproduce the complex effects of the incoming boundary layer from the ITD.

3D Reynolds Stress Modelling of Turbulent Flow in Linear Turbine Cascade

1997 ◽  
Author(s):  
M. Kanniche ◽  
R. Boudjemadi ◽  
F. Déjean ◽  
F. Archambeau
Keyword(s):  
Reynolds Stress ◽  
Eddy Viscosity ◽  
Strain Tensor ◽  
Secondary Flows ◽  
Turbulence Closure ◽  
Turbine Cascade ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Principal Axes ◽  
The Mean

The flow in a linear turbine cascade (Gregory-Smith et al. (1990)) is numerically investigated using a Reynolds Stress Turbulence closure. A particular attention is given to secondary flows where the normal Reynolds stresses are expected to play an important role. The most classical turbulence closure, the k-epsilon model uses the Boussinesq Eddy Viscosity concept which assumes an isotropic turbulent viscosity. The Reynolds stresses are then related to local velocity gradients by this isotropic eddy viscosity. Corollary, the principal axes of the Reynolds stress tensor are colinear with those of the mean strain tensor. The advantage of Reynolds Stress Turbulence closure is the calculation of Reynolds stresses by their own individual transport equations. This leads to a more realistic description of the turbulence and of its dependance on the mean flow. The most classical Second Order turbulence model (Launder et al. (1975)) is applied to a linear turbine cascade, and the results are compared to secondary velocity and turbulence measurements at cross-passage planes.

Separated and Reattached Flow Over Square, Rectangular and Semi-Circular Blocks

2007 ◽  
Author(s):  
M. Agelinchaab ◽  
M. F. Tachie
Keyword(s):  
Boundary Layer ◽  
Cross Sections ◽  
Recirculation Region ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Block Height ◽  
Turbulent Statistics ◽  
Image Velocimetry ◽  
The Mean ◽  
Separated And Reattached Flow

A particle image velocimetry is used to study the characteristics of separated and reattached turbulent flow over two-dimensional transverse blocks of square, rectangular and semi-circular cross-sections fixed to the bottom wall of an open channel. The ratio of upstream boundary layer thickness to block height is considerably higher than in prior studies. The results show that the mean and turbulent statistics in the recirculation region and downstream of reattachment are significantly different from the upstream boundary layer. The variation of the Reynolds stresses along the separating streamlines is discussed within the context of vortex stretching, longitudinal strain rate and wall damping. It appears wall damping is a more dominant mechanism in the vicinity of reattachment. The levels of turbulence diffusion and production by the normal stresses are significantly higher than in classical turbulent boundary layers. The bulk of turbulence production occurs in mid-layer and transported into the inner and outer layers. The results also reveal that the curvature of separating streamline, separating bubble beneath it as well as the mean velocity and turbulent quantities depend strongly on block geometry.

Scaling of Favorable Pressure Gradient Turbulent Boundary Layers With Eventual Relaminarization

2005 ◽  
Author(s):  
Rau´l Bayoa´n Cal ◽  
Xia Wang ◽  
Luciano Castillo
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Reynolds Shear Stress ◽  
Velocity Profiles ◽  
Turbulent Boundary Layers ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Favorable Pressure Gradient ◽  
The Mean

Applying similarity analysis to the RANS equations of motion for a pressure gradient turbulent boundary layer, Castillo and George [1] obtained the scalings for the mean deficit velocity and the Reynolds stresses. Following this analysis, Castillo and George studied favorable pressure gradient (FPG) turbulent boundary layers. They were able to obtain a single curve for FPG flows when scaling the mean deficit velocity profiles. In this study, FPG turbulent boundary layers are analyzed as well as relaminarized boundary layers subjected to an even stronger FPG. It is found that the mean deficit velocity profiles diminish when scaled using the Castillo and George [1] scaling, U∞, and the Zagarola and Smits [2] scaling, U∞δ*/δ. In addition, Reynolds stress data has been analyzed and it is found that the relaminarized boundary layer data decreases drastically in all components of the Reynolds stresses. Furthermore, it will be shown that the shape of the profile for the wall-normal and Reynolds shear stress components change drastically given the relaminarized state. Therefore, the mean velocity deficit profiles as well as Reynolds stresses are found to be necessary in order to understand not only FPG flows, but also relaminarized boundary layers.

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