scholarly journals Influences of trailing boundary layer velocity profiles on wake vortex formation in a high-subsonic-turbine cascade

2018 ◽  
Vol 233 (2) ◽  
pp. 186-198 ◽  
Author(s):  
Shuai Wang ◽  
Fengbo Wen ◽  
Shibo Zhang ◽  
Shenzhan Zhang ◽  
Xun Zhou
Keyword(s):  
Boundary Layer ◽  
Temporal Stability ◽  
Vortex Formation ◽  
Velocity Profiles ◽  
Wake Flow ◽  
Wake Vortex ◽  
Suction Surface ◽  
Wake Flows ◽  
Number Formula ◽  
Unsteady Effect

In this paper, delayed detached eddy simulations are performed to study wake flows of a turbine blade at a high subsonic exit Mach number, [Formula: see text], and high Reynolds number, [Formula: see text], based on the chord length and outlet velocity. It is found that a slight change in the trailing suction profile would have a big influence on the formation of wake vortex street, which is believed to be caused by the change in the boundary layer state near the trailing edge, and suction boundary layer with a fuller velocity profile tends to destabilize the wake flow, promoting the generation of wake vortex and enhancing the unsteady effect. Local spatial-temporal stability analyses of the wake velocity profiles suggest that wake flows with asymmetric velocity profiles might have a stabilizing effect. It is suggested that the vortex formation and its strength can be controlled by making some slight modifications on the rear blade suction surface, and the mixing loss in the wake can be reduced due to a weaker unsteady effect.

Wake Interaction of a Square Cylinder With a Splitter Plate Boundary Layer at a Low Reynolds Number

2015 ◽  
Author(s):  
Smriti Srivastava ◽  
Sudipto Sarkar
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Bluff Body ◽  
Acoustic Noise ◽  
Vortex Formation ◽  
Plate Boundary ◽  
Wake Flow ◽  
Stream Velocity ◽  
Square Cylinder ◽  
Plate Length

One of the most important researches in bluff body aerodynamics is to control the shear layer evolution leading to vortex formation. This kind of research is closely associated with reduction of aerodynamics forces and acoustic noise. Passive and active control of wake-flow from bluff bodies have received a great deal of attention in the last few decades [1–4]. Keeping this in mind, authors investigate the interaction of a square cylinder (side of the square = a) wake with a flat plate (length L = a, width w = 0.1a) boundary layer positioned at various downstream locations close to the cylinder. The gap-to-side ratios are maintained at G/a = 0, 0.5, 1 and 2 (where G is the gap between square cylinder and plate), and the simulation is performed at a Reynolds number, Re = 100 (Re = U∞a/v, where U∞ is free stream velocity and v is kinematic viscosity). Instantaneous flow visualization, aerodynamic forces and vortex shedding frequencies for all cases are described to gain insight about the changes associated with wake of the cylinder when a short plate is kept in its downstream.

Experimental Study of the Effect of Periodic Unsteady Wake Flow on Boundary Layer Development, Separation, and Reattachment Along the Surface of a Low Pressure Turbine Blade

2004 ◽  
Vol 126 (4) ◽  
pp. 663-676 ◽  
Author(s):  
M. T. Schobeiri ◽  
B. O¨ztu¨rk
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Wake Flow ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Reduced Frequency ◽  
Boundary Layer Development ◽  
Unsteady Wake ◽  
Unsteady Wake Flow ◽  
Layer Development

The paper experimentally studies the effects of periodic unsteady wake flow on boundary layer development, separation and reattachment along the suction surface of a low pressure turbine blade. The experimental investigations were performed on a large scale, subsonic unsteady turbine cascade research facility at the Turbomachinery Performance and Flow Research Laboratory (TPFL), Texas A&M University. The experiments were carried out at a Reynolds number of 110,000 (based on suction surface length and exit velocity) with a free-stream turbulence intensity of 1.9%. One steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, wake velocities, and turbulence intensities were investigated. The reduced frequencies cover the entire operating range of LP turbines. In addition to the unsteady boundary layer measurements, blade surface measurements were performed at the same Reynolds number. The surface pressure measurements were also carried out at one steady and two periodic unsteady inlet flow conditions. The results presented in ensemble-averaged, and the contour plot forms help to understand the physics of the separation phenomenon under periodic unsteady wake flow. It was found that the suction surface displayed a strong separation bubble for these three different reduced frequencies. For each condition, the locations and the heights defining the separation bubble were determined by carefully analyzing and examining the pressure and the mean velocity profile data. The location of boundary layer separation was independent of the reduced frequency level. However, the extent of the separation was strongly dependent on the reduced frequency level. Once the unsteady wake started to penetrate into the separation bubble, the turbulent spot produced in the wake paths caused a reduction of the separation bubble height.

Experimental Study of the Effect of Periodic Unsteady Wake Flow on Boundary Layer Development, Separation, and Re-Attachment Along the Surface of a Low Pressure Turbine Blade

2004 ◽  
Author(s):  
M. T. Schobeiri ◽  
B. O¨ztu¨rk
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Wake Flow ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Reduced Frequency ◽  
Boundary Layer Development ◽  
Unsteady Wake ◽  
Unsteady Wake Flow ◽  
Layer Development

The paper experimentally studies the effects of periodic unsteady wake flow on boundary layer development, separation and re-attachment along the suction surface of a low pressure turbine blade. The experimental investigations were performed on a large scale, subsonic unsteady turbine cascade research facility at Turbomachinery Performance and Flow Research Laboratory (TPFL), Texas A&M University. The experiments were carried out at a Reynolds number of 110,000 (based on suction surface length and exit velocity) with a free-stream turbulence intensity of 1.9%. One steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, wake velocities, and turbulence intensities were investigated. The reduced frequencies cover the entire operating range of LP turbines. In addition to the unsteady boundary layer measurements, blade surface measurements were performed at the same Reynolds number. The surface pressure measurements were also carried out at one steady and two periodic unsteady inlet flow conditions. The results presented in ensemble-averaged, and the contour plot forms help to understand the physics of the separation phenomenon under periodic unsteady wake flow. It was found that the suction surface displayed a strong separation bubble for these three different reduced frequencies. For each condition, the locations and the heights defining the separation bubble were determined by carefully analyzing and examining the pressure and the mean velocity profile data. The location of boundary layer separation was independent of the reduced frequency level. However, the extent of the separation was strongly dependent on the reduced frequency level. Once the unsteady wake started to penetrate into the separation bubble, the turbulent spot produced in the wake paths caused a reduction of the separation bubble height.

scholarly journals Intermittent Behavior of the Separated Boundary Layer Along the Suction Surface of a Low Pressure Turbine Blade Under Periodic Unsteady Flow Conditions

2005 ◽  
Author(s):  
B. O¨ztu¨rk ◽  
M. T. Schobeiri ◽  
David E. Ashpis
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Low Pressure ◽  
Boundary Layer Transition ◽  
Wake Flow ◽  
Unsteady Boundary Layer ◽  
Flow Conditions ◽  
Suction Surface ◽  
Low Pressure Turbine

The paper experimentally and theoretically studies the effects of periodic unsteady wake flow and aerodynamic characteristics on boundary layer development, separation and re-attachment along the suction surface of a low pressure turbine blade. The experiments were carried out at Reynolds number of 110,000 (based on suction surface length and exit velocity). For one steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, intermittency behavior were experimentally and theoretically investigated. The current investigation attempts to extend the intermittency unsteady boundary layer transition model developed in previously to the LPT cases, where separation occurs on the suction surface at a low Reynolds number. The results of the unsteady boundary layer measurements and the intermittency analysis were presented in the ensemble-averaged, and contour plot forms. The analysis of the boundary layer experimental data with the flow separation, confirms the universal character of the relative intermittency function which is described by a Gausssian function.

A Comparison of the Wake Effects Generated by the Biased Triangle Bar and Traditional Cylinder Bar to the Boundary Layer on Suction Surface of LPT Blade

2020 ◽  
Vol 37 (2) ◽  
pp. 153-166
Author(s):  
Sun Shuang ◽  
Li Wei ◽  
Lu Xin’gen ◽  
Zhang Yanfeng ◽  
Zhu Junqiang ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Near Field ◽  
Flow Characteristics ◽  
Wake Flow ◽  
Cylinder Wake ◽  
Suction Surface ◽  
Wake Effects ◽  
The Asymmetry ◽  
Layer Flow

AbstractConsidering the asymmetry of the low pressure turbine blade (LPT) wake at a low Reynolds number, the influence of asymmetric wakes which are similar to LPT wakes on the boundary layer of downstream blade rows in the near field is studied in the present paper, in order to increase wake flow prediction accuracy of the downstream blade without increasing the difficulty of the experiment or calculation load. Packb high-lift LPT airfoil was studied with CFX software. Following the analysis of the similarities between the wake generated by the cylinder bar and the triangle bar and the LPT blade wake in the near-field, the boundary layer flow characteristics on the suction surface under the different wakes were compared. In this research, it was found that the wakes of biased triangle bar shared more similarities with the LPT blade wake in the near field than the cylinder bar. Furthermore, the biased triangle bar wake was asymmetrical in terms of its centerline, and the separation bubble was suppressed while the calming effect was reduced after the wake-induced transition due to the asymmetry. And the time-averaged momentum thickness decreased by 7 % compared to the cylinder wake.

scholarly journals On the Physics of Flow Separation Along a Low Pressure Turbine Blade Under Unsteady Flow Conditions

2005 ◽  
Vol 127 (3) ◽  
pp. 503-513 ◽  
Author(s):  
Meinhard T. Schobeiri ◽  
Burak Öztürk ◽  
David E. Ashpis
Keyword(s):  
Boundary Layer ◽  
Test Section ◽  
Separation Zone ◽  
Wake Flow ◽  
Unsteady Boundary Layer ◽  
Flow Conditions ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Unsteady Wake ◽  
Unsteady Wake Flow

The present study, which is the first of a series of investigations dealing with specific issues of low pressure turbine (LPT) boundary layer aerodynamics, is aimed at providing detailed unsteady boundary flow information to understand the underlying physics of the inception, onset, and extent of the separation zone. A detailed experimental study on the behavior of the separation zone on the suction surface of a highly loaded LPT-blade under periodic unsteady wake flow is presented. Experimental investigations were performed at Texas A&M Turbomachinery Performance and Flow Research Laboratory using a large-scale unsteady turbine cascade research facility with an integrated wake generator and test section unit. To account for a high flow deflection of LPT-cascades at design and off-design operating points, the entire wake generator and test section unit including the traversing system is designed to allow a precise angle adjustment of the cascade relative to the incoming flow. This is done by a hydraulic platform, which simultaneously lifts and rotates the wake generator and test section unit. The unit is then attached to the tunnel exit nozzle with an angular accuracy of better than 0.05°, which is measured electronically. Utilizing a Reynolds number of 110,000 based on the blade suction surface length and the exit velocity, one steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, wake velocities and turbulence intensities are investigated using hot-wire anemometry. In addition to the unsteady boundary layer measurements, blade surface pressure measurements were performed at Re=50,000, 75,000, 100,000, and 125,000 at one steady and two periodic unsteady inlet flow conditions. Detailed unsteady boundary layer measurement identifies the onset and extent of the separation zone as well as its behavior under unsteady wake flow. The results presented in ensemble-averaged and contour plot forms contribute to understanding the physics of the separation phenomenon under periodic unsteady wake flow. Several physical mechanisms are discussed.

Boundary Layer Measurement on the Blade Surface of a Multi-Stage Axial Flow Compressor

2003 ◽  
Author(s):  
Y. H. Shin ◽  
R. L. Elder ◽  
I. Bennett
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Axial Flow ◽  
Velocity Profiles ◽  
Surface Boundary ◽  
Blade Surface ◽  
Suction Surface ◽  
Axial Flow Compressor ◽  
Layer Flow ◽  
Flow Compressor

This study presents experimental investigations into blade suction surface boundary layer flow in a multistage axial flow compressor. The experiments were focused on the third stage of the 4-stage Low Speed Research Compressor (LSRC) at Cranfield University. Measurements within the boundary layer were obtained using a hot wire probe. This was traversed normal to the blade surface at small increments, capturing the unsteady velocity profile within the boundary layer. Detailed boundary layer flow measurements covering most of the stator suction surface were taken and are described using time mean and ensemble averaged velocity profiles. Turbulence intensity in the boundary layer flow on the blade suction surface is also discussed. A strong wake-induced strip zone due to passing wake disturbances are generated at midspan near the blade leading edge at rotor blade passing frequency. Corner separation was observed at the tip region near the trailing edge. Normalized velocity profiles in this region show no variation in time.

Effect of Turbulence Intensity and Periodic Unsteady Wake Flow Condition on Boundary Layer Development, Separation, and Re-Attachment Over the Separation Bubble Along the Suction Surface of a Low Pressure Turbine Blade

2006 ◽  
Author(s):  
B. O¨ztu¨rk ◽  
M. T. Schobeiri
Keyword(s):  
Boundary Layer ◽  
Turbine Blade ◽  
Separation Zone ◽  
Separation Bubble ◽  
Wake Flow ◽  
Combined Effects ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Unsteady Wake ◽  
Unsteady Wake Flow

The paper experimentally investigates the individual and combined effects of periodic unsteady wake flows and freestream turbulence intensity (FSTI) on flow separation along the suction surface of a low pressure turbine blade. The experiments were carried out at a Reynolds number of 110,000 based on the suction surface length and the cascade exit velocity. The experimental matrix includes freestream turbulence intensities of 1.9%, 3.0%, 8.0%, 13.0% and three different unsteady wake frequencies with the steady inlet flow as the reference configuration. Detailed boundary layer measurements are performed along the suction surface of a highly loaded turbine blade with a separation zone. Particular attention is paid to the aerodynamic behavior of the separation zone at different FSTIs at steady and periodic unsteady flow conditions. The objective of the research is (a) to quantify the effect of FSTIs on the dynamics of the separation bubble at steady inlet flow condition, and (b) to investigate the combined effects of FSTI and the unsteady wake flow on the behavior of the separation bubble. The experimental investigations were performed on a large scale, subsonic unsteady turbine cascade research facility at the Turbomachinery Performance and Flow Research Laboratory (TPFL) of Texas A&M University.

scholarly journals Effect of Reynolds Number and Periodic Unsteady Wake Flow Condition on Boundary Layer Development, Separation, and Re-Attachment Along the Suction Surface of a Low Pressure Turbine Blade

2005 ◽  
Author(s):  
B. O¨ztu¨rk ◽  
M. T. Schobeiri ◽  
David E. Ashpis
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Separation Bubble ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Boundary Layer Development ◽  
Unsteady Wake ◽  
Unsteady Wake Flow

The paper experimentally studies the effects of periodic unsteady wake flow and different Reynolds numbers on boundary layer development, separation and re-attachment along the suction surface of a low pressure turbine blade. The experimental investigations were performed on a large scale, subsonic unsteady turbine cascade research facility at Turbomachinery Performance and Flow Research Laboratory (TPFL) of Texas A&M University. The experiments were carried out at Reynolds numbers of 110,000 and 150,000 (based on suction surface length and exit velocity). One steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, wake velocities, and turbulence intensities were investigated. The reduced frequencies chosen cover the operating range of LP turbines. In addition to the unsteady boundary layer measurements, surface pressure measurements were performed. The inception, onset, and the extent of the separation bubble information collected from the pressure measurements were compared with the hot wire measurements. The results presented in ensemble-averaged, and the contour plot forms help to understand the physics of the separation phenomenon under periodic unsteady wake flow and different Reynolds number. It was found that the suction surface displayed a strong separation bubble for these three different reduced frequencies. For each condition, the locations defining the separation bubble were determined carefully analyzing and examining the pressure and mean velocity profile data. The location of the boundary layer separation was dependent of the Reynolds number. It is observed that starting point of the separation bubble and the re-attachment point move further downstream by increasing Reynolds number from 110,000 to 150,000. Also, the size of the separation bubble is smaller when compared to that for Re = 110,000.

scholarly journals Effect of Reynolds Number and Periodic Unsteady Wake Flow Condition on Boundary Layer Development, Separation, and Intermittency Behavior Along the Suction Surface of a Low Pressure Turbine Blade

2005 ◽  
Vol 129 (1) ◽  
pp. 92-107 ◽  
Author(s):  
M. T. Schobeiri ◽  
B. Öztürk ◽  
David E. Ashpis
Keyword(s):  
Boundary Layer ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Boundary Layer Development ◽  
Unsteady Wake ◽  
Unsteady Wake Flow ◽  
Layer Development ◽  
Intermittency Analysis

The paper experimentally studies the effects of periodic unsteady wake flow and Reynolds number on boundary layer development, separation, reattachment, and the intermittency behavior along the suction surface of a low pressure turbine blade. Extensive unsteady boundary layer experiments were carried out at Reynolds numbers of 110,000 and 150,000 based on suction surface length and exit velocity. One steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, wake velocities, and turbulence intensities were investigated. The analysis of the experimental data reveals details of boundary layer separation dynamics which is essential for understanding the physics of the separation phenomenon under periodic unsteady wake flow and different Reynolds numbers. To provide a complete picture of the transition process and separation dynamics, extensive intermittency analysis was conducted. Ensemble-averaged maximum and minimum intermittency functions were determined, leading to the relative intermittency function. In addition, the detailed intermittency analysis was aimed at answering the question as to whether the relative intermittency of a separated flow fulfills the universality criterion.

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