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.

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.

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.

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.

Effects of periodic wakes on boundary layer development on an ultra-high-lift low pressure turbine airfoil

2016 ◽  
Vol 231 (1) ◽  
pp. 25-38 ◽  
Author(s):  
Xingen Lu ◽  
Yanfeng Zhang ◽  
Wei Li ◽  
Shuzhen Hu ◽  
Junqiang Zhu
Keyword(s):  
Boundary Layer ◽  
Transition Process ◽  
Low Pressure ◽  
Suction Surface ◽  
High Lift ◽  
Low Pressure Turbine ◽  
Turbulent Transition ◽  
Boundary Layer Development ◽  
Unsteady Wake ◽  
Layer Development

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.

Effects of Reynolds Number and Freestream Turbulence Intensity on the Unsteady Boundary Layer Development on an Ultra-High-Lift Low Pressure Turbine Airfoil

2009 ◽  
Vol 132 (1) ◽  
Author(s):  
Xue Feng Zhang ◽  
Howard Hodson
Keyword(s):  
Boundary Layer ◽  
Reynolds Numbers ◽  
Freestream Turbulence ◽  
Unsteady Boundary Layer ◽  
Suction Surface ◽  
High Lift ◽  
Low Pressure Turbine ◽  
Boundary Layer Development ◽  
Unsteady Wake ◽  
Layer Development

The effects of Reynolds numbers and the freestream turbulence intensities (FSTIs) on the unsteady boundary layer development on an ultra-high-lift low-pressure turbine airfoil, so-called T106C, are investigated. The measurements were carried out at both Tu=0.5% and 4.0% within a range of Reynolds numbers, based on the blade chord and the isentropic exit velocity, between 100,000 and 260,000. The interaction between the unsteady wake and the boundary layer depends on both the strength of the wake and the status of the boundary layer. At Tu=0.5%, both the wake’s high turbulence and the negative jet behavior of the wake dominate the interaction between the unsteady wake and the separated boundary layer on the suction surface of the airfoil. Since the wake turbulence cannot induce transition before separation on this ultra-high-lift blade, the negative jet of the wake has the opportunity to induce a rollup vortex. At Tu=4.0%, the time-mean separation on the suction surface is much smaller. With elevated FSTI, the turbulence in the wake just above the boundary layer is no longer distinguishable from the background turbulence level. The unsteady boundary layer transition is dominated by the wake’s negative jet induced boundary layer variation.

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.

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

2006 ◽  
Vol 129 (6) ◽  
pp. 747-763 ◽  
Author(s):  
B. Öztürk ◽  
M. T. Schobeiri
Keyword(s):  
Turbine Blade ◽  
Separation Zone ◽  
Separation Bubble ◽  
Wake Flow ◽  
Combined Effects ◽  
Flow Conditions ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Unsteady Wake ◽  
Unsteady Wake Flow

This 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%, and 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 (i) to quantify the effect of FSTIs on the dynamics of the separation bubble at steady inlet flow conditions and (ii) to investigate the combined effects of Tuin and the unsteady wake flow on the behavior of the separation bubble.

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

2003 ◽  
Author(s):  
Meinhard T. Schobeiri ◽  
Burak O¨ztu¨rk ◽  
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.

Effects of Turbulence and Solidity on the Boundary Layer Development in a Low Pressure Turbine

2000 ◽  
Author(s):  
W. J. Solomon
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Boundary Layer Transition ◽  
Turbulence Level ◽  
Suction Surface ◽  
Layer Transition ◽  
Laminar Separation ◽  
Second Stage ◽  
Boundary Layer Development ◽  
Layer Development

Multiple-element surface hot-film instrumentation has been used to investigate boundary layer development in the 2 stage Low Speed Research Turbine (LSRT). Measurements from instrumentation located along the suction surface of the second stage nozzle at mid-span are presented. These results contrast the unsteady, wake-induced boundary layer transition behaviour for various turbine configurations. The boundary layer development on two new turbine blading configurations with identical design vector diagrams but substantially different loading levels are compared with a previously published result. For the conventional loading (Zweifel coefficient) designs, the boundary layer transition occurred without laminar separation. At reduced solidity, wake-induced transition started upstream of a laminar separation line and an intermittent separation bubble developed between the wake-influenced areas. A turbulence grid was installed upstream of the LSRT turbine inlet to increase the turbulence level from about 1% for clean-inlet to about 5% with the grid. The effect of turbulence on the transition onset location was smaller for the reduced solidity design than the baseline. At the high turbulence level, the amplitude of the streamwise fluctuation of the wake-induced transition onset point was reduced considerably. By clocking the first stage nozzle row relative to the second, the alignment of the wake-street from the first stage nozzle with the suction surface of the second stage nozzle was varied. At particular wake clocking alignments, the periodicity of wake induced transition was almost completely eliminated.

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