The Effect of Leading-Edge Geometry on Wake Interactions in Compressors

2007 ◽  
Author(s):  
Andrew P. S. Wheeler ◽  
Alessandro Sofia ◽  
Robert J. Miller
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Surface Profile ◽  
Leading Edge ◽  
Suction Surface ◽  
Pressure Surface ◽  
Edge Geometry ◽  
Boundary Layer Interaction ◽  
Wake Interactions ◽  
Stator Blade

The effect of leading-edge geometry on wake/boundary-layer interaction was studied in a low-speed single-stage HP compressor. Both a 3:1 elliptic and circular leading-edge were tested on a Controlled Diffusion (CDA) stator-blade. Experiments were undertaken on the stator suction-surface, these included hotwire boundary-layer traverses, surface hotfilm measurements and high resolution leading-edge pressure measurements. Steady CFD predictions were also performed to aid the interpretation of the results. The two leading-edge shapes gave rise to significantly different flows. For the blade with the elliptic leading-edge (Blade A), the leading-edge boundary-layer remained attached and laminar in the absence of wakes. The wake presence led to the formation of a thickened laminar boundary-layer in which turbulent disturbances were observed to form. Measurements of the trailing-edge boundary-layer indicated that the wake/leading interaction for Blade A raised the suction-surface loss by 20%. For the blade with the circular leading-edge (Blade B) the leading-edge boundary-layer exhibited a separation bubble, which was observed to reattach laminar in the absence of wakes. The presence of the wake moved the separation position forwards whilst inducing a turbulent reattachment upstream of the time-average reattachment position. This produced a region of very high momentum thickness at the leading-edge. The suction-surface profile loss was found to be 38% higher for Blade B compared to Blade A. The total loss (suction-surface and pressure-surface) for Blade B was measured to be 32% higher than that of Blade A.

The Effect of Leading-Edge Geometry on Wake Interactions in Compressors

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Andrew P. S. Wheeler ◽  
Alessandro Sofia ◽  
Robert J. Miller
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Leading Edge ◽  
Suction Surface ◽  
Surface Loss ◽  
Edge Geometry ◽  
Boundary Layer Interaction ◽  
Wake Interactions ◽  
Stator Blade ◽  
Profile Loss

The effect of leading-edge geometry on the wake/boundary-layer interaction was studied in a low-speed single-stage HP compressor. Both a 3:1 elliptic and a circular leading edge were tested on a controlled diffusion aerofoil stator blade. Experiments were undertaken on the stator suction surface; these included hotwire boundary-layer traverses, surface hotfilm measurements, and high resolution leading-edge pressure measurements. Steady computational fluid dynamics (CFD) predictions were also performed to aid the interpretation of the results. The two leading-edge shapes gave rise to significantly different flows. For a blade with an elliptic leading edge (Blade A), the leading-edge boundary layer remained attached and laminar in the absence of wakes. The wake presence led to the formation of a thickened laminar boundary layer in which turbulent disturbances were observed to form. Measurements of the trailing-edge boundary layer indicated that the wake/leading-edge interaction for Blade A raised the suction-surface loss by 20%. For a blade with a circular leading edge (Blade B), the leading-edge boundary-layer exhibited a separation bubble, which was observed to reattach laminar in the absence of wakes. The presence of the wake moved the separation position forward while inducing a turbulent reattachment upstream of the leading-edge time-average reattachment position. This produced a region of very high momentum thickness at the leading edge. The suction-surface loss was found to be 38% higher for Blade B than for Blade A. Wake traverses downstream of the blades were used to determine the total profile loss of each blade. The profile loss of Blade B was measured to be 32% higher than that of Blade A.

Unsteady Flow in Oscillating Turbine Cascade: Part 1 — Linear Cascade Experiment

1996 ◽  
Author(s):  
L. He
Keyword(s):  
Computational Study ◽  
Separation Bubble ◽  
Turbine Blades ◽  
Leading Edge ◽  
Computational Method ◽  
Reattachment Point ◽  
Suction Surface ◽  
Linear Cascade ◽  
Unsteady Pressure ◽  
Pressure Surface

An experimental and computational study has been carried out on a linear cascade of low pressure turbine blades with the middle blade oscillating in a torsion mode. The main objectives of the present work were to enhance understanding of the behaviour of bubble type of flow separation and to examine the predictive ability of a computational method. In addition, an attempt was made to address a general modelling issue: was the linear assumption adequately valid for such kind of flow? In Part 1 of this paper, the experimental work was described. Unsteady pressure was measured along blade surfaces using off-board mounted pressure transducers at realistic reduced frequency conditions. A short separation bubble on the suction surface near the trailing edge and a long leading-edge separation bubble on the pressure surface were identified. It was found that in the regions of separation bubbles, unsteady pressure was largely influenced by the movement of reattachment point, featured by an abrupt phase shift and an amplitude trough in the 1st harmonic distribution. The short bubble on the suction surface seemed to follow closely a laminar bubble transition model in a quasi-steady manner, and had a localized effect. The leading-edge long bubble on the pressure surface, on the other hand, was featured by a large movement of the reattachment point, which affected the surface unsteady pressure distribution substantially. As far as the aerodynamic damping was concerned, there was a destabilizing effect in the separated flow region, which was however largely balanced by the stabilizing effect downstream of the reattachment point due to the abrupt phase change.

The Measurement of Boundary Layers on a Compressor Blade in Cascade: Part 4 — Flow Fields for Incidence Angles of −1.5 and −8.5 Degrees

1989 ◽  
Author(s):  
W. C. Zierke ◽  
S. Deutsch
Keyword(s):  
Boundary Layers ◽  
Separation Bubble ◽  
Measurement Techniques ◽  
Leading Edge ◽  
Compressor Blade ◽  
Laser Doppler ◽  
Laser Doppler Velocimeter ◽  
Suction Surface ◽  
Laminar Separation ◽  
Pressure Surface

Measurements, made with laser Doppler velocimetry, about a double-circular-arc compressor blade in cascade are presented for −1.5 and −8.5 degree incidence angles and a chord Reynolds number near 500,000. Comparisons between the results of the current study and those of our earlier work at a 5.0 degree incidence are made. It is found that in spite of the relative sophistication of the measurement techniques, transition on the pressure surface at the −1.5 degree incidence is dominated by a separation “bubble” too small to be detected by the laser Doppler velocimeter. The development of the boundary layers at −1.5 and 5.0 degrees are found to be similar. In contrast to the flow at these two incidence angles, the leading edge separation “bubble” is on the pressure surface for the −8.5 degree incidence. Here, all of the measured boundary layers on the pressure surface are turbulent — but extremely thin — while on the suction surface, a laminar separation/turbulent reattachment “bubble” lies between roughly 35% and 60% chord. This “bubble” is quite thin, and some problems in interpreting backflow data.

Leading Edge Contamination of a C-D Compressor Blade Using Large Eddy Simulation

2020 ◽  
Author(s):  
S. Katiyar ◽  
S. Sarkar
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Separation Bubble ◽  
Leading Edge ◽  
Adverse Pressure Gradient ◽  
Suction Surface ◽  
Local Flow ◽  
Flow Acceleration ◽  
Eddy Simulation ◽  
Large Eddy

Abstract A large-eddy simulation (LES) is employed here to predict the flow field over the suction surface of a controlled-diffusion (C-D) compressor stator blade following the experiment of Hobson et al. [1]. When compared with the experiment, LES depicts a separation bubble (SB) in the mid-chord region of the suction surface, although discrepancies exist in Cp. Further, the LES resolves the growth of boundary layer over the mid-chord and levels of turbulence intensity with an acceptable limit. What is noteworthy that LES also resolves a tiny SB near the leading-edge at the designed inflow angle of 38.3°. The objective of the present study is to assess how this leading-edge bubble influences the transition and development of boundary layer on the suction surface before the mid-chord. It appears that the separation at leading-edge suddenly enhances the perturbation levels exciting development of boundary layer downstream. The boundary layer becomes pre-transitional followed by a decay of fluctuations up to 30% of chord attributing to the local flow acceleration. Further, the boundary layer appears like laminar after being relaxed from the leading edge excitation near the mid-chord. It separates again because of the adverse pressure gradient, depicting augmentation of turbulence followed by the breakdown at about 70% of chord.

Observations of Transition Phenomena on a Controlled Diffusion Compressor Stator With a Circular Arc Leading Edge

2007 ◽  
Author(s):  
Alan D. Henderson ◽  
Gregory J. Walker
Keyword(s):  
Boundary Layer ◽  
Turbulent Flow ◽  
Surface Profile ◽  
Leading Edge ◽  
Suction Surface ◽  
Circular Arc ◽  
Flow Acceleration ◽  
Controlled Diffusion ◽  
Numerical Predictions ◽  
Wide Range

Laminar-turbulent transition behavior is studied near the leading edge of an outlet stator blade in a low-speed 1.5-stage axial-flow research compressor. The stator is a typical controlled diffusion design with a circular arc leading edge profile. Slow response surface pressure distribution measurements are compared with numerical predictions from the quasi two-dimensional flow solver, MISES. These both show a strong flow acceleration around each side of the circular arc, followed by a rapid deceleration near each blend point of the arc to the main surface profile. The relative magnitude of the localized overspeeds varies significantly over the wide range of stator flow incidence investigated. The unsteady boundary layer behavior on the stator is studied using a midspan array of surface-mounted hot-film sensors. On the suction surface, wake-induced transitional and turbulent strips are observed to originate close to the leading edge. The boundary layer approaches separation near the leading edge blend point on the suction surface, but this does not always lead to localized turbulent breakdown or continuous turbulent flow: a significant portion of the flow on the forward part of the surface remains laminar between the wake-induced transitional strips. At high positive incidence the wake-induced transitional strips originate near the leading edge blend point, but their growth is suppressed by the strong flow acceleration. On the pressure surface, a small separation bubble forms near the leading edge blend point resulting in almost continuous turbulent flow over the whole incidence range studied.

The Influence of Diffuser Vane Leading Edge Geometry on the Performance of a Centrifugal Compressor

1989 ◽  
Author(s):  
W. W. Clements ◽  
D. W. Artt
Keyword(s):  
Centrifugal Compressor ◽  
Surface Profile ◽  
Leading Edge ◽  
Radius Ratio ◽  
Suction Surface ◽  
Edge Geometry ◽  
Edge Radius ◽  
Compressor Performance ◽  
Series Of Experiments ◽  
Stage Performance

A series of experiments was carried out on two turbocharger compressors to determine the influence of pressure face angle, semi-vaneless space suction surface profile and diffuser leading edge radius ratio on stage performance. It was found that whilst compressor performance was virtually unaffected by changes in pressure face angle, performance was sensitive to changes in the semi-vaneless space suction surface profile. Straight wedge diffusers produced higher stage efficiencies than any diffuser with a concave suction surface profile between the leading edge and throat. Optimum stage performance was achieved with diffuser leading edge radius ratios between 1.06 and 1.10.

Effect of Leading-Edge Geometry on Separation Bubble on a Compressor Blade

2003 ◽  
Author(s):  
Huoxing Liu ◽  
Baojie Liu ◽  
Ling Li ◽  
Haokang Jiang
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Separation Bubble ◽  
Research Work ◽  
Wedge Angle ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Test Model ◽  
Edge Geometry ◽  
Separation Bubbles

Accurate prediction of flow field is the most important factor during the design of high performance compressors. In some cases the agreement of pressure ratio and efficiency between predicted and measured is excellent, but it is common for the efficiency to be in error by perhaps one or two percent. This error is enough to render the calculation unable to replace expensive experiment testing. One of the important matters in need of more study is the mechanism of boundary layer transition from laminar to turbulent flow. The objective of this fundamental research work is to acquire the detailed structure of separation bubbles on the suction side of the blade by using the PIV and pressure taps. This paper presents an experimental study of the influence of 2d leading-edge geometry on behavior of separation bubbles. The measurements on a nose of enlarged blade were conducted on a special large-scale experimental facility, the pressure distribution and flowfield of flow were measured. The test model used in this study consists of circular leading edge and elliptic leading edge. Results are presented for a range of incidence. The measurement result indicated that the leading edge shape has a large influence on flow details separation and transition as well as the boundary layer properties after reattached point. The wedge angle appears to be an important role in leading edge geometry parameters.

scholarly journals Measured and Calculated Wall Temperatures on Air-Cooled Turbine Vanes With Boundary Layer Transition

1983 ◽  
Author(s):  
Curt H. Liebert ◽  
Raymond E. Gaugler ◽  
Herbert J. Gladden
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
High Reynolds Number ◽  
Separation Bubble ◽  
Boundary Layer Transition ◽  
Suction Surface ◽  
Layer Transition ◽  
Pressure Surface ◽  
Lower Reynolds Number ◽  
High Reynolds

Convection cooled turbine vane metal wall temperatures experimentally obtained in a hot cascade for a given one-vane design were compared with wall temperatures calculated with TACT1 and STAN5 computer codes which incorporated various models for predicting laminar-to-turbulent boundary layer transition. Favorable comparisons on both vane surfaces were obtained at high Reynolds number with only one of these transition models. When other models were used, temperature differences between calculated and experimental data obtained at the high Reynolds number were as much as 14 percent in the separation bubble region of the pressure surface. On the suction surface and at lower Reynolds number, predictions and data unsatisfactorily differed by as much as 22 percent. Temperature differences of this magnitude can represent orders of magnitude error in blade life prediction.

The Effect of Hub Inlet Boundary Layer Skewing on the Endwall Shear Flow in an Annular Turbine Cascade

1979 ◽  
Author(s):  
J. P. Bindon
Keyword(s):  
Boundary Layer ◽  
Leading Edge ◽  
High Energy ◽  
Surface Flow ◽  
Inlet Section ◽  
Turbine Cascade ◽  
Suction Surface ◽  
Pressure Surface ◽  
Displacement Thickness ◽  
Real Machine

The inner annulus endwall boundary layer between the blades was examined experimentally in an annular turbine cascade for conditions of inlet boundary layer skewing similar to that in a real machine and for the collateral inlet as in all cascade tests. Skewing was introduced by rotating the hub ahead of the cascade. The slot created ahead of the cascade by the rotating hub caused major changes in the endwall surface flow visualization patterns seen as compared to an uninterrupted inlet section. Skewing did not alter the basic pattern except to increase the surface crossflow angles. Traverses taken at 15 points between the blades showed a sharp thickening followed by sharp thinning of the boundary layer near the pressure surface leading edge. The overall distribution of displacement thickness was not greatly influenced by skewing and generally showed a thicker layer near the suction surface and an extremely thin layer near the pressure surface at exit. Skewing increased significantly the amount of fluid involved in crossflow. While surface crossflow angles were everywhere greater with increasing inlet skewing, the increases were more marked in the mid to upper reaches of the shear layer. Loss profiles near the inlet showed the presence of high energy fluid near the surface but near the exit skewed and collateral profiles were more similar.

CFD Prediction of Boundary Layer Transition and Separation on an Airfoil at Varying Angle of Attack

2007 ◽  
Author(s):  
Nicole M. Wolgemuth ◽  
D. Keith Walters
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Turbulence Models ◽  
Leading Edge ◽  
Boundary Layer Separation ◽  
Boundary Layer Transition ◽  
Suction Surface ◽  
Layer Transition ◽  
Turbulent Airflow ◽  
Naca 0012

This study analyzes the predicted flow over a NACA 0012 airfoil at varying angles of attack and three different Reynolds numbers. The ability of three different turbulence models to predict boundary layer separation and transition behavior is investigated. Particular interest is paid to prediction of the separation bubble that develops near the leading edge of the airfoil suction surface prior to stall. The FLUENT CFD solver was used to simulate turbulent airflow over the airfoil. The three turbulence models include the standard and realizable forms of the k-ε model, available in FLUENT, as well as a recently developed transition-sensitive k-ω model that was implemented into the solver using user-defined functions. By employing the new, transition-sensitive model, computed properties of the flow field were found to be closer to experimental data than results produced by utilizing built-in turbulence models. Most importantly, the new, transition-sensitive model predicts the occurrence of the separation bubble, which the other models are unable to predict. The new model also clearly reproduces the laminar, transitional, and turbulent flow that occurs over the airfoil.

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