Experimental Investigation of a High-Lift Low-Pressure Turbine Suction Surface

AIAA Journal ◽  
2010 ◽  
Vol 48 (11) ◽  
pp. 2465-2471 ◽  
Author(s):  
Mark McQuilling ◽  
Mitch Wolff ◽  
Sergey Fonov ◽  
Jim Crafton ◽  
Rolf Sondergaard
Keyword(s):  
Experimental Investigation ◽  
Low Pressure ◽  
Suction Surface ◽  
High Lift ◽  
Low Pressure Turbine

Effect of Unsteady Wakes on Boundary Layer Separation on a Very High Lift Low Pressure Turbine Airfoil

2010 ◽  
Author(s):  
Ralph J. Volino
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Separation ◽  
Low Pressure ◽  
Freestream Turbulence ◽  
Suction Surface ◽  
High Lift ◽  
Layer Separation ◽  
Low Pressure Turbine ◽  
Wake Passing ◽  
Very High

Boundary layer separation has been studied on a very high lift, low-pressure turbine airfoil in the presence of unsteady wakes. Experiments were done under low (0.6%) and high (4%) freestream turbulence conditions on a linear cascade in a low speed wind tunnel. Wakes were produced from moving rods upstream of the cascade. Flow coefficients were varied from 0.35 to 1.4 and wake spacing was varied from 1 to 2 blade spacings, resulting in dimensionless wake passing frequencies F = fLj-te/Uave (f is the frequency, Lj-te is the length of the adverse pressure gradient region on the suction surface of the airfoils, and Uave is the average freestream velocity) ranging from 0.14 to 0.56. Pressure surveys on the airfoil surface and downstream total pressure loss surveys were documented. Instantaneous velocity profile measurements were acquired in the suction surface boundary layer and downstream of the cascade. Cases were considered at Reynolds numbers (based on the suction surface length and the nominal exit velocity from the cascade) of 25,000 and 50,000. In cases without wakes, the boundary layer separated and did not reattach. With wakes, separation was largely suppressed, particularly if the wake passing frequency was sufficiently high. At lower frequencies the boundary layer separated between wakes. Background freestream turbulence had some effect on separation, but its role was secondary to the wake effect.

Effects of Surface Groove on Separated Flow Transition on a High-Lift Low-Pressure Turbine Profile Under Steady Inflow Conditions

2009 ◽  
Author(s):  
Hualing Luo ◽  
Weiyang Qiao ◽  
Kaifu Xu
Keyword(s):  
Boundary Layer ◽  
Separated Flow ◽  
Low Pressure ◽  
Separation Point ◽  
Flow Transition ◽  
Suction Surface ◽  
High Lift ◽  
Low Pressure Turbine ◽  
Surface Groove ◽  
Inflow Conditions

LES (Large-Eddy Simulation) computations for a high-lift low-pressure turbine profile equipped with the span-wise groove on the suction surface are done to investigate the mechanism of the surface groove for separated flow transition control under steady inflow conditions, employing the dynamic Smagorinsky model. In addition to the baseline case (no groove), three groove positions which depend on the relative position of the groove trailing edge and the separation point on the suction surface are considered at two Reynolds numbers (Re, based on the inlet velocity and axial chord length). The results show that all grooves can reduce the calculated loss for Re = 50000, due to the further upstream transition inception in the separated shear layer. The analyses indicate two kinds of control mechanism such as the thinning of boundary layer behind the groove and the introduction of disturbances within the groove, depending on the groove position and Reynolds number. At Re = 50000, for the groove located upstream of the separation point, the reason for the further upstream transition inception location is the thinning of boundary layer behind the groove, and for the groove located downstream of the separation point, the reason is the introduction of disturbances within the groove. At Re = 100000, disturbances can also be generated within the groove located upstream of the separation point, promoting earlier transition inception.

Separation Control on a Very High Lift Low Pressure Turbine Airfoil Using Pulsed Vortex Generator Jets

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Ralph J. Volino ◽  
Olga Kartuzova ◽  
Mounir B. Ibrahim
Keyword(s):  
Boundary Layer ◽  
Total Pressure ◽  
Vortex Generator ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Separation Control ◽  
Suction Surface ◽  
High Lift ◽  
Low Pressure Turbine ◽  
Very High

Boundary layer separation control has been studied using vortex generator jets (VGJs) on a very high lift, low-pressure turbine airfoil. Experiments were done under high (4%) freestream turbulence conditions on a linear cascade in a low speed wind tunnel. Pressure surveys on the airfoil surface and downstream total pressure loss surveys were documented. Instantaneous velocity profile measurements were acquired in the suction surface boundary layer. Cases were considered at Reynolds numbers (based on the suction surface length and the nominal exit velocity from the cascade) of 25,000 and 50,000. Jet pulsing frequency, duty cycle, and blowing ratio were all varied. Computational results from a large eddy simulation of one case showed reattachment in agreement with the experiment. In cases without flow control, the boundary layer separated and did not reattach. With the VGJs, separation control was possible even at the lowest Reynolds number. Pulsed VGJs were more effective than steady jets. At sufficiently high pulsing frequencies, separation control was possible even with low jet velocities and low duty cycles. At lower frequencies, higher jet velocity was required, particularly at low Reynolds numbers. Effective separation control resulted in an increase in lift and a reduction in total pressure losses. Phase averaged velocity profiles and wavelet spectra of the velocity show the VGJ disturbance causes the boundary layer to reattach, but that it can reseparate between disturbances. When the disturbances occur at high enough frequency, the time available for separation is reduced, and the separation bubble remains closed at all times.

Secondary Flow Loss Reduction Through Blowing for a High-Lift Front-Loaded Low Pressure Turbine Cascade

2012 ◽  
Vol 135 (2) ◽  
Author(s):  
Stuart I. Benton ◽  
Jeffrey P. Bons ◽  
Rolf Sondergaard
Keyword(s):  
Reynolds Number ◽  
Pressure Loss ◽  
Total Pressure ◽  
Control Method ◽  
Low Pressure ◽  
Total Pressure Loss ◽  
Suction Surface ◽  
High Lift ◽  
Blade Loading ◽  
Low Pressure Turbine

Efforts to increase individual blade loading in the low pressure turbine have resulted in blade geometries optimized for midspan performance. Many researchers have shown that increased blade loading and a front-loaded pressure distribution each separately contribute to increased losses in the endwall region. A detailed investigation of the baseline endwall flow of the L2F profile, which is a high-lift front loaded profile, is performed. In-plane velocity vectors and total pressure loss maps are obtained in five planes oriented normal to the blade surface for three Reynolds numbers. A row of pitched and skewed jets are introduced near the endwall on the suction surface of the blade. The flow control method is evaluated for four momentum coefficients at the high Reynolds number, with a maximum reduction of 42% in the area averaged total pressure loss coefficient. The same blade is also fitted with midspan vortex-generator jets and is tested at a Reynolds number of 20,000, resulting in a 21% reduction in the area averaged total pressure loss.

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.

Generation and Development of Klebanoff Streaks in Low-Pressure Turbine Cascade Under Upstream Wakes

2020 ◽  
Author(s):  
Shuang Sun ◽  
Xingshuang Wu ◽  
Tianrong Tan ◽  
Canlin Zuo ◽  
Sirui Pan ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Separation Bubble ◽  
Transition Process ◽  
Low Pressure ◽  
Suction Surface ◽  
High Lift ◽  
Low Pressure Turbine ◽  
Wall Shear

Abstract At low Reynolds numbers operating condition, the boundary layer of the high-lift low-pressure turbine (LPT) of aero-engines is prone to separate on the suction surface of the airfoil. The profile losses of the airfoil are largely governed by the size of the separation bubble and the transition process in the boundary layer. However, the wake-induced transition, the natural transition and the instability induced by the Klebanoff streaks complicate the transition process. The boundary layer on the suction surface of a high-lift LPT was investigated at Re = 50,000 with upstream wakes. The numerical simulation was performed with the CFX software using large eddy simulations (LES), and the experiment was performed on a linear cascade. In this study, the wake is divided into the wake center and the wake tail, the unsteady formation process of the streaks and the wall shear stress caused by the wake are analyzed. A new mechanism of generation and development of Klebanoff Streaks was presented to better understand the effect of the wake on the boundary layer. Moreover, it was found that after entering the blade passage, the wake center does not contact the blade but causes the wall shear stress of the front part on the suction surface to increase. However, it is not possible to form strong Klebanoff streaks at the leading edge of the blade by shear sheltering effect. Only the wake tail can form Klebanoff streaks when it contacts the blade.

The Effect of FSTI to the Combined Separation Control Strategy of Surface Roughness With Upstream Wakes

2016 ◽  
Author(s):  
Sun Shuang ◽  
Lei Zhi-jun ◽  
Lu Xin-gen ◽  
Zhang Yan-feng ◽  
Zhu Jun-qiang
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Reynolds Number ◽  
Transition Region ◽  
Boundary Layer Separation ◽  
Low Pressure ◽  
Suction Surface ◽  
High Lift ◽  
Number Range ◽  
Low Pressure Turbine

Boundary layer separation can lead to partial loss of lift and higher aerodynamic losses on low-pressure turbine airfoils at low Reynolds number in high bypass ratio engines. The combined effects of upstream wakes and surface roughness on boundary layer development have been investigated experimentally to improve the performance of ultra-high-lift low-pressure turbine (LPT) blades. The measurement was performed on a linear cascade with an ultra-high-lift aft-loaded LP turbine profile named IET-LPTA with Zweifel loading coefficient of about 1.37. The wakes were simulated by the moving cylindrical bars upstream of the cascade. The time-mean aerodynamic performance and the boundary layer behavior on suction surface had been measured with two 3-hole probes and a hot-wire probe. Three roughness heights ranging from 8.8–20.9μm combined with three roughness deposit positions ranging from 5.2%–39.5% suction surface length formed a large measurement matrix. The roughness with height of 8.8μm (1.05×10−4 chord length) covering 5.2% suction surface reduced the profile loss across the whole Reynolds number range. Under the effect of roughness associated with upstream wakes, the freestream turbulence intensity (FSTI) is responsible in part for the development of the wake-induced transition region, calmed region and natural transition region of the boundary layer. The transition length and the transition onset of the boundary layer were also affected by the FSTI.

Effect of Unsteady Wakes on Boundary Layer Separation on a Very High Lift Low Pressure Turbine Airfoil

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
Ralph J. Volino
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Separation ◽  
Low Pressure ◽  
Freestream Turbulence ◽  
Suction Surface ◽  
High Lift ◽  
Layer Separation ◽  
Low Pressure Turbine ◽  
Wake Passing ◽  
Very High

Boundary layer separation has been studied on a very high lift, low pressure turbine airfoil in the presence of unsteady wakes. Experiments were done under low (0.6%) and high (4%) freestream turbulence conditions on a linear cascade in a low speed wind tunnel. Wakes were produced from moving rods upstream of the cascade. Flow coefficients were varied from 0.35 to 1.4 and wake spacing was varied from one to two blade spacings, resulting in dimensionless wake passing frequencies F=fLj-te/Uave (f is the frequency, Lj-te is the length of the adverse pressure gradient region on the suction surface of the airfoils, and Uave is the average freestream velocity) ranging from 0.14 to 0.56. Pressure surveys on the airfoil surface and downstream total pressure loss surveys were documented. Instantaneous velocity profile measurements were acquired in the suction surface boundary layer and downstream of the cascade. Cases were considered at Reynolds numbers (based on the suction surface length and the nominal exit velocity from the cascade) of 25,000 and 50,000. In cases without wakes, the boundary layer separated and did not reattach. With wakes, separation was largely suppressed, particularly if the wake passing frequency was sufficiently high. At lower frequencies the boundary layer separated between wakes. Background freestream turbulence had some effect on separation, but its role was secondary to the wake effect.

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