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.

Separated Flow Measurements on a Highly Loaded Low-Pressure Turbine Airfoil

2008 ◽  
Author(s):  
Ralph J. Volino
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Separation Bubble ◽  
Boundary Layer Separation ◽  
Low Pressure ◽  
Transition To Turbulence ◽  
Suction Surface ◽  
Airfoil Surface ◽  
Flow Measurements ◽  
Low Pressure Turbine

Boundary layer separation, transition and reattachment have been studied on a new, very high lift, low-pressure turbine airfoil. Experiments were done under low 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. Velocity profiles were acquired in the suction side boundary layer at several streamwise locations using hot-wire anemometry. Cases were considered at Reynolds numbers (based on the suction surface length and the nominal exit velocity from the cascade) ranging from 25,000 to 330,000. In all cases the boundary layer separated, but at high Reynolds number the separation bubble remained very thin and quickly reattached after transition to turbulence. In the low Reynolds number cases, the boundary layer separated and did not reattach, even when transition occurred. This behavior contrasts with previous research on other airfoils, in which transition, if it occurred, always induced reattachment, regardless of Reynolds number.

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.

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.

Separated Flow Measurements on a Highly Loaded Low-Pressure Turbine Airfoil

2009 ◽  
Vol 132 (1) ◽  
Author(s):  
Ralph J. Volino
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Separation Bubble ◽  
Boundary Layer Separation ◽  
Low Pressure ◽  
Transition To Turbulence ◽  
Suction Surface ◽  
Airfoil Surface ◽  
Flow Measurements ◽  
Low Pressure Turbine

Boundary layer separation, transition, and reattachment have been studied on a new, very high lift, low-pressure turbine airfoil. Experiments were done under low 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. Velocity profiles were acquired in the suction side boundary layer at several streamwise locations using hot-wire anemometry. Cases were considered at Reynolds numbers (based on the suction surface length and the nominal exit velocity from the cascade) ranging from 25,000 to 330,000. In all cases, the boundary layer separated, but at high Reynolds number the separation bubble remained very thin and quickly reattached after transition to turbulence. In the low Reynolds number cases, the boundary layer separated and did not reattach, even when transition occurred. This behavior contrasts with previous research on other airfoils, in which transition, if it occurred, always induced reattachment, regardless of Reynolds number.

Numerical Study on Flow Separation Control for High-Lift Low-Pressure Turbine Split Blade

2013 ◽  
Author(s):  
Jianhui Chen ◽  
Huancheng Qu ◽  
Ping Li ◽  
Yage Li ◽  
Yonghui Xie ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Flow Control ◽  
Flow Separation ◽  
Axial Direction ◽  
Low Pressure ◽  
Chord Length ◽  
Suction Surface ◽  
High Lift ◽  
Low Pressure Turbine

The low-pressure high-lift blade aims to reduce blades number for reducing manufacturing cost, but the flow separation is easy to appear on the boundary layer of low-pressure turbine cascade under operating condition with low Reynolds number, which will significantly decreases the efficiency and safety of turbine blade and even the whole engine. Flow control on boundary layer of the cascade can reduce flow separation and improve the aerodynamic performance of low-pressure high-loaded turbine. In this study, a new flow control approach called split blade is applied on the LPT (low pressure turbine) PakB. This technology is a passive flow control method by using the jet created by different pressure of two points on the blade surface to control the boundary layer separation on the suction surface. Different operating conditions were investigated including flow separation on PakB cascade without control and cascade with slot at four kinds of Reynolds number (Re = 25000, Re = 50000, Re = 75000, Re = 100000) (based on the chord length in axial direction). The outlet of the slot is located upstream of the separation point on the boundary layer which is 0.68Cax (chord length in axial direction) on the suction surface, the inclination angle of slot is 30°, the diameter of slot is 2mm. Detailed flow characteristics, separation and reattachment locations are presented at the different Reynolds numbers were presented in this paper. The results show that without control the separation location on the boundary layer of the cascade moves downstream with the increase of Reynolds number while the reattachment location moves up. The results also show that at Reynolds number is 25000, as different pressure of slots two ends is low, the jets velocity is low and the control effect is not obvious. At other three kinds of Reynolds number, the reattachment location moves up separation zones decreases due to the flow control.

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.

The Influence of Mach Number on the Boundary Layer Development of High-Lift Low Pressure Turbine in Low Reynolds Number

2020 ◽  
Author(s):  
Wenhua Duan ◽  
Jian Liu ◽  
Weiyang Qiao
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Mach Number ◽  
Turbine Blade ◽  
Low Reynolds Number ◽  
Low Pressure ◽  
High Lift ◽  
Low Pressure Turbine ◽  
Boundary Layer Development ◽  
Layer Development

Abstract A numerical analysis of the effect of Mach number on the boundary layer development and aerodynamic performance of a high-lift, after loaded low pressure turbine blade is presented in this paper. The turbine blade is designed for the GTF engine and works in a low Reynolds number, high Mach number environment. Three different isentropic exit Mach numbers (0.14, 0.87 and 1.17) are simulated by large eddy simulation method, while the Reynolds number based on the axial chord length of the blade and the exit flow velocity is kept the same (1 × 105). The condition Mais,2 = 0.14 represents the lowspeeed wind tunnel environment which is usually used in the low pressure turbine investigation. The condition Mais,2 = 0.87 represents the design point of the turbine blade. The condition Mais,2 = 1.17 represents the severe environment when the shock wave shows up. A comparison of the boundary layer development is made and the total pressure loss results from the boundary layer is discussed.

Development of Blade Profiles for Low Pressure Turbine Applications

1996 ◽  
Author(s):  
E. M. Curtis ◽  
H. P. Hodson ◽  
M. R. Banieghbal ◽  
J. D. Denton ◽  
R. J. Howell ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Surface Pressure ◽  
Low Pressure ◽  
Blade Profile ◽  
Suction Surface ◽  
Number Range ◽  
Low Pressure Turbine ◽  
Pressure Distributions ◽  
Wide Range ◽  
Highly Loaded

This paper describes a programme of work, largely experimental, which was undertaken with the objective of developing an improved blade profile for the low-pressure turbine in aero-engine applications. Preliminary experiments were conducted using a novel technique. An existing cascade of datum blades was modified to enable the pressure distribution on the suction surface of one of the blades to be altered. Various means, such as shaped inserts, an adjustable flap at the trailing edge, and changing stagger were employed to change the geometry of the passage. These experiments provided boundary layer and lift data for a wide range of suction surface pressure distributions. The data was then used as a guide for the development of new blade profiles. The new blade profiles were then investigated in a low-speed cascade that included a set of moving bars upstream of the cascade of blades 10 simulate the effect of the incoming wakes from the previous blade row in a multistage turbine environment. Results are presented for two improved profiles that are compared with a datum representative of current practice. The experimental results include loss measurements by wake traverse, surface pressure distributions, and boundary layer measurements. The cascades were operated over a Reynolds Number range from 0.7 × 105 to 4.0 × 105. The first profile is a “laminar flow” design that was intended to improve the efficiency at the same loading as the datum. The other is a more highly loaded blade profile intended to permit a reduction in blade numbers. The more highly loaded profile is the most promising candidate for inclusion in future designs. It enables blade numbers to be reduced by 20%, without incurring any efficiency penalty. The results also indicate that unsteady effects must be taken into consideration when selecting a blade profile for the low-pressure turbine.

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