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.

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.

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.

Experimental and Computational Investigations of Separation and Transition on a Highly Loaded Low-Pressure Turbine Airfoil: Part 1 — Low Freestream Turbulence Intensity

2008 ◽  
Author(s):  
Mounir Ibrahim ◽  
Olga Kartuzova ◽  
Ralph J. Volino
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Transport Model ◽  
Separation Bubble ◽  
Pressure Coefficient ◽  
Low Pressure ◽  
Transition To Turbulence ◽  
Transition Model ◽  
Freestream Turbulence ◽  
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. Three different CFD URANS (unsteady Reynolds averaged Navier-Stokes) models were utilized in this study (using Fluent CFD Code), the k-ω shear stress transport model, the ν2-fk-ε model, and the 4 equation Transition model of Menter. At Re = 25,000, the Transition model seems to perform the best. At Re = 100,000 the Transition model seems to perform the best also, although it under-predicts the pressure coefficient downstream of the suction peak. At Re = 300,000 all models perform very similar with each other. The Transition model showed a small bump in the pressure coefficient downstream from the suction peak indicating the presence of a small bubble at that location.

Designing Low-Pressure Turbine Blades With Integrated Flow Control

2005 ◽  
Author(s):  
Jeffrey P. Bons ◽  
Laura C. Hansen ◽  
John P. Clark ◽  
Peter J. Koch ◽  
Rolf Sondergaard
Keyword(s):  
Reynolds Number ◽  
Flow Control ◽  
Turbine Blade ◽  
Separation Bubble ◽  
Low Pressure ◽  
Suction Surface ◽  
Flow Measurements ◽  
Blade Loading ◽  
Low Pressure Turbine ◽  
Wide Range

A low pressure turbine blade was designed to produce a 17% increase in blade loading over an industry-standard airfoil using integrated flow control to prevent separation. The design was accomplished using two-dimensional CFD predictions of blade performance coupled with insight gleaned from recently published work in transition modeling and from previous experiments with flow control using vortex generator jets (VGJs). In order to mitigate the Reynolds number lapse in efficiency associated with LPT airfoils, a mid-loaded blade was selected. Also, separation predictions from the computations were used to guide the placement of control actuators on the blade suction surface. Three blades were fabricated using the new design and installed in a two-passage linear cascade facility. Flow velocity and surface pressure measurements taken without activating the VGJs indicate a large separation bubble centered at 68% axial chord on the suction surface. The size of the separation and its growth with decreasing Reynolds number agree well with CFD predictions. The separation bubble reattaches to the blade over a wide range of inlet Reynolds numbers from 150,000 down to below 20,000. This represents a marked improvement in separation resistance compared to the original blade profile which separates without reattachment below a Reynolds number of 40,000. This enhanced performance is achieved by increasing the blade spacing while simultaneously adjusting the blade shape to make it less aft-loaded but with a higher peak cp. This reduces the severity of the adverse pressure gradient in the uncovered portion of the modified blade passage. With the use of pulsed VGJs, the design blade loading was achieved while providing attached flow over the entire range of Re. Detailed phase-locked flow measurements using three-component PIV show the trajectory of the jet and its interaction with the unsteady separation bubble. Results illustrate the importance of integrating flow control into the turbine blade design process and the potential for enhanced turbine performance.

Study of Flow Controlling on LP Turbine at Different Reynolds Number

2012 ◽  
Author(s):  
Muhammad Aqib Chishty ◽  
Hossein Raza Hamdani ◽  
Khalid Parvez ◽  
Muhammad Nafees Mumtaz Qadri
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Flow Separation ◽  
Separation Bubble ◽  
Low Pressure ◽  
Control Flow ◽  
Loss Coefficient ◽  
Shear Stresses ◽  
Low Pressure Turbine ◽  
Lp Turbine

Active and passive techniques have been used in the past, to control flow separation. Numerous studies were published on controlling and delaying the flow separation on low pressure turbine. In this study, a single dimple (i.e. passive device) is engraved on the suction side of LP turbine cascade T106A. The main aim of this research is to find out the optimum parameters of dimple i.e. diameter (D) and depth (h) which can produce strong enough vortex that can control the flow either in transition or fully turbulent phase. Furthermore, this optimal dimple is engraved to suppress the boundary layer separation at different Reynolds number (based on the chord length and inlet velocity). The dimple of different depth and diameter are used to find the optimal depth to diameter ratio. Computational results show that the optimal ratio of depth to diameter (h/D) for dimple is 0.0845 and depth to grid boundary layer (h/δ) is 0.5152. This optimized dimple efficiently reduces the normalized loss coefficient and it is found that the negative values of shear stresses found in uncontrolled case are being removed by the dimple. After that, dimple of optimized parameters are used to suppress the laminar separation bubble at different Re∼25000, 50000 and 91000. It was noticed that the dimple did not reduce the losses at Re∼25000. But at Re∼50000, it produced such a strong vortex that reduced the normalized loss coefficient to 25%, while 5% losses were reduced at Re∼91000. It can be concluded that the optimized dimple effectively controlled flow separation and reduced normalized loss coefficient from Re 25000 to 91000. As the losses are decreased, this will increase the low pressure turbine efficiency and reduce its fuel consumption.

scholarly journals Effect of Reynolds Number on Separation Bubbles on Controlled-Diffusion Compressor Blades in Cascade

1998 ◽  
Author(s):  
Garth V. Hobson ◽  
Denis J. Hansen ◽  
David G. Schnorenberg ◽  
Darren V. Grove
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Separation Bubble ◽  
Boundary Layer Separation ◽  
Surface Flow ◽  
Flow Reversal ◽  
Surface Boundary ◽  
Suction Surface ◽  
Flow Angle ◽  
Controlled Diffusion

A detailed experimental investigation of second-generation, controlled-diffusion, compressor stator blades at an off-design inlet-flow angle was performed in a low-speed cascade wind tunnel primarily using laser-Doppler velocimetry (LDV). The object of the study was to characterize the off-design flowfield and to obtain LDV measurements of the suction surface boundary layer separation which occurred near mid chord. The effect of Reynolds number on the flow separation in the regime of 210,000 to 640,000 was investigated. Surface flow visualization showed that at the low Re. no. the mid-chord separation bubble started laminar and reattached turbulent within 20% chord on the suction side of the blade. The extent of the bubble compared very well with the measured blade surface pressure distribution which showed a classical plateau and then diffusion in the turbulent region. LDV measurements of the flow reversal in the bubble were performed. At the intermediate Re. no. the boundary layer was transitional before the bubble which had decreased significantly in size (down to 10% chord). At the highest Re. no. the flow was turbulent from close to the leading edge, and three-dimensional flow reversal as a result of endwall effects appeared at approximately 80% chord which did not reattach.

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.

Aerodynamic Measurements on a Low Pressure Turbine Cascade With Different Levels of Distributed Roughness

2011 ◽  
Author(s):  
Marco Montis ◽  
Reinhard Niehuis ◽  
Andreas Fiala
Keyword(s):  
Boundary Layer ◽  
High Speed ◽  
Separation Bubble ◽  
Reference Conditions ◽  
Suction Side ◽  
Boundary Layer Separation ◽  
Low Pressure ◽  
Average Roughness ◽  
Low Pressure Turbine ◽  
High Reynolds

The effect of surface roughness on the aerodynamics of a highly loaded low-pressure turbine airfoil was investigated in a series of cascade tests conducted in a high speed facility. Profile loss and aerodynamic loading of three different surface roughnesses with a ratio of the centerline average roughness to the profile chord of 1.1 · 10−5, 7.1 · 10−5 and 29 · 10−5 were analysed. Tests were carried out under design outlet Mach number, outlet Reynolds number ranging from 5 · 104 to 7 · 105 and inlet turbulence level of 2.5% and 5%. The mid span flow field downstream of the cascade and the loading distribution on the profile were measured for each investigated operating point using a five hole probe and surface static pressure taps. Additional measurements with a hot wire probe in the profile boundary layer under reference conditions (Re2th = 2 · 105) were also conducted. Experimental results show a loss reduction for the highest roughness under reference conditions, due to the partial suppression of the separation bubble on the suction side of the profile. At high Reynolds numbers a massive boundary layer separation on the suction side is observed for the highest roughness, along with a large increase in total pressure loss. The middle roughness tested has no effect on the loading distribution as well as on the loss behaviour of the airfoil under all investigated flow conditions.

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.

A Comparison of Three Low Pressure Turbine Designs

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Christian T. Wakelam ◽  
Martin Hoeger ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Total Pressure ◽  
Maximum Velocity ◽  
Suction Side ◽  
Low Pressure ◽  
Surface Boundary ◽  
Suction Surface ◽  
Pressure Losses ◽  
Low Pressure Turbine

As part of the current research, three low pressure turbine (LPT) geometries—which were designed with a common pitch, axial chord, inlet angle, and exit Mach number and to create the same nominal level of turning—are compared. Each of the LPT cascades was investigated under a range of Reynolds numbers, exit Mach numbers, and under the influence of a moving bar wake generator. Profile static pressure distributions, wake traverses at 5% and 40% axial chord downstream of the trailing edge, and suction side boundary layer traverses were used to compare the performance of the three designs. The total pressure losses are strongly dependent on both the maximum velocity location as well as the diffusion on the suction surface. The importance of the behavior of the pressure surface boundary layer turned out to be negligible in comparison. Cases with equivalent operating Reynolds number and suction side diffusion level are compared in terms of the total pressure losses that are generated. It is shown that a relationship between loss and suction side maximum velocity location exists. An optimum suction side maximum velocity location depends on the Reynolds number, diffusion factor, and wake passing frequency.

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