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.

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.

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.

scholarly journals Measurements in Separated and Transitional Boundary Layers Under Low-Pressure Turbine Airfoil Conditions

2000 ◽  
Vol 123 (2) ◽  
pp. 189-197 ◽  
Author(s):  
Ralph J. Volino ◽  
Lennart S. Hultgren
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Free Stream ◽  
Separation Bubble ◽  
Low Pressure ◽  
Mean Velocity ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine

Detailed velocity measurements were made along a flat plate subject to the same dimensionless pressure gradient as the suction side of a modern low-pressure turbine airfoil. Reynolds numbers based on wetted plate length and nominal exit velocity were varied from 50,000 to 300,000, covering cruise to takeoff conditions. Low and high inlet free-stream turbulence intensities (0.2 and 7 percent) were set using passive grids. The location of boundary-layer separation does not depend strongly on the free-stream turbulence level or Reynolds number, as long as the boundary layer remains nonturbulent prior to separation. Strong acceleration prevents transition on the upstream part of the plate in all cases. Both free-stream turbulence and Reynolds number have strong effects on transition in the adverse pressure gradient region. Under low free-stream turbulence conditions, transition is induced by instability waves in the shear layer of the separation bubble. Reattachment generally occurs at the transition start. At Re=50,000 the separation bubble does not close before the trailing edge of the modeled airfoil. At higher Re, transition moves upstream, and the boundary layer reattaches. With high free-stream turbulence levels, transition appears to occur in a bypass mode, similar to that in attached boundary layers. Transition moves upstream, resulting in shorter separation regions. At Re above 200,000, transition begins before separation. Mean velocity, turbulence, and intermittency profiles are presented.

scholarly journals Measurements in Separated and Transitional Boundary Layers Under Low-Pressure Turbine Airfoil Conditions

2000 ◽  
Author(s):  
Ralph J. Volino ◽  
Lennart S. Hultgren
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Free Stream ◽  
Separation Bubble ◽  
Low Pressure ◽  
Mean Velocity ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine

Detailed velocity measurements were made along a flat plate subject to the same dimensionless pressure gradient as the suction side of a modern low-pressure turbine airfoil. Reynolds numbers based on wetted plate length and nominal exit velocity were varied from 50, 000 to 300, 000, covering cruise to takeoff conditions. Low and high inlet free-stream turbulence intensities (0.2% and 7%) were set using passive grids. The location of boundary-layer separation does not depend strongly on the free-stream turbulence level or Reynolds number, as long as the boundary layer remains non-turbulent prior to separation. Strong acceleration prevents transition on the upstream part of the plate in all cases. Both free-stream turbulence and Reynolds number have strong effects on transition in the adverse pressure gradient region. Under low free-stream turbulence conditions transition is induced by instability waves in the shear layer of the separation bubble. Reattachment generally occurs at the transition start. At Re = 50, 000 the separation bubble does not close before the trailing edge of the modeled airfoil. At higher Re, transition moves upstream, and the boundary layer reattaches. With high free-stream turbulence levels, transition appears to occur in a bypass mode, similar to that in attached boundary layers. Transition moves upstream, resulting in shorter separation regions. At Re above 200,000, transition begins before separation. Mean velocity, turbulence and intermittency profiles are presented.

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.

An Experimental Investigation of the Wake Shed From a High-Lift Low Pressure Turbine Cascade at Different Reynolds Numbers

2008 ◽  
Author(s):  
Francesca Satta ◽  
Marina Ubaldi ◽  
Pietro Zunino ◽  
Claudia Schipani
Keyword(s):  
Boundary Layer ◽  
Experimental Investigation ◽  
Reynolds Number ◽  
Separation Bubble ◽  
Suction Side ◽  
Low Pressure ◽  
Profile Measurement ◽  
High Lift ◽  
Low Pressure Turbine ◽  
Lower Reynolds Number

The paper presents the results of an experimental investigation of the wake shed from a high-lift low-pressure turbine profile. Measurement campaigns have been carried out in a three-blade large-scale turbine linear cascade. The Reynolds number based on the chord length has been varied in the range 100000–500000, to differentiate the influence of the boundary layer separation on the wake development. Two Reynolds number conditions, representative of the typical working conditions of a low pressure aeroengine turbine, have been more extensively investigated. Mean velocity and Reynolds stress components within the wake shed from the central blade have been measured across the wake by means of a two-component crossed miniature hotwire probe. The measuring traverses were located at distances ranging between 2 and 100% of the blade chord from the central blade trailing edge. Moreover, wake integral parameters, at the two Reynolds conditions, have been evaluated and compared. Both velocity and total pressure results show a wider wake occurring at the lower Reynolds number, due to the separation affecting the suction side boundary layer. Furthermore, the momentum thickness has been found to be much higher at the lower Reynolds number, due to the higher losses related to the separation bubble occurring on the blade suction side. The Strouhal number associated with the vortex shedding seems to be influenced by the Reynolds number, due to the different conditions of the suction side boundary layers.

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.

Transition Prediction in Low Pressure Turbine (LPT) Using Gamma Theta Model and Passive Control of Separation

2011 ◽  
Author(s):  
Muhammad Aqib Chishty ◽  
Khalid Parvez ◽  
Sijal Ahmed ◽  
Hossein Raza Hamdani ◽  
Ammar Mushtaq
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Passive Control ◽  
Stokes Equations ◽  
Separation Bubble ◽  
Turbine Blades ◽  
Low Pressure ◽  
Computational Domain ◽  
High Lift ◽  
Low Pressure Turbine

The boundary layer of low-pressure turbine blades has received a great deal of attention due to advent of high lift and ultra high lift LP turbines. At cruising condition, Reynolds number is very low in engine and LP turbine performance suffers mainly from losses due to the laminar separation bubble on suction surface. In this paper, T106A low pressure turbine profile has been used to study the behavior of boundary layer and subsequently, flow is controlled using the passive technique. Unsteady Reynolds Averaged Navier Stokes equations were solved using SST Gamma-Theta transition model for turbulence closure. Hybrid mesh topology has been used to discretize the computational domain, with highly resolved structured mesh in boundary layer (Y+ < 1) and unstructured mesh in the rest of domain. Simulations were performed using commercial CFD code ANSYS FLUENT ® at Reynolds number 91000 (based on inlet velocity and chord length) and turbulence intensity of 0.4%. To study the effect of dimple on the flow separation, dimple has been positioned at different axial location on the suction side. It was found that shifting the dimple downstream results in controlled flow and reduced loss coefficient as compared to the case when no dimple is applied.

scholarly journals Direct Numerical Simulation on the Unsteady Flow Field of Low-Pressure Turbine Cascades With and Without Upstream Wake at Low Reynolds Number

2021 ◽  
Author(s):  
Xiyuan Pang ◽  
Hongbo Zhu ◽  
Feng Wu ◽  
Yan Bao ◽  
Hui Xu
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Flow Separation ◽  
Low Reynolds Number ◽  
Low Pressure ◽  
Aerodynamic Performance ◽  
High Fidelity ◽  
Low Pressure Turbine ◽  
Turbine Cascades ◽  
Element Method

Abstract The spectral/hp element method is a high fidelity method that has good numerical dispersion-diffusion characteristics and is flexible and applicable to quasi-three-dimensional aerodynamic problems with complex geometric configurations in the streamline direction and the pitch direction. This paper uses this method to directly solve the incompressible Navier-Stokes equations, and analyzes the aerodynamic performance of the T106A low-pressure turbine cascade at low Reynolds number. Two different conditions, i.e. uniform inlet flow and cylinder’s wake flow, are adopted and their basic characteristics of flow separation and transition are quantitatively analyzed and compared, by observing the distribution of cascade wall surface pressure and friction coefficient, the distribution of wake profile pressure loss and the evolution characteristics of boundary layer flow structure. The numerical results show that the spectral/hp element method can accurately predict the flow separation and transition performance of low-pressure turbine cascades, which implies that it can be used as a high-fidelity simulation and calculation tool for the optimal design of this type of cascade. It is also found that cylinder’s wake can effectively inhibit boundary layer separation of the T106A LPT blade and improve aerodynamic performance and efficiency of it.

The Effect of Pulsed Blowing on the Boundary Layer of a Highly Loaded Low Pressure Turbine Blade

2013 ◽  
Author(s):  
Marion Mack ◽  
Roland Brachmanski ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Mach Number ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Trailing Edge ◽  
Low Pressure Turbine ◽  
Wide Range ◽  
Highly Loaded

The performance of the low pressure turbine (LPT) can vary appreciably, because this component operates under a wide range of Reynolds numbers. At higher Reynolds numbers, mid and aft loaded profiles have the advantage that transition of suction side boundary layer happens further downstream than at front loaded profiles, resulting in lower profile loss. At lower Reynolds numbers, aft loading of the blade can mean that if a suction side separation exists, it may remain open up to the trailing edge. This is especially the case when blade lift is increased via increased pitch to chord ratio. There is a trend in research towards exploring the effect of coupling boundary layer control with highly loaded turbine blades, in order to maximize performance over the full relevant Reynolds number range. In an earlier work, pulsed blowing with fluidic oscillators was shown to be effective in reducing the extent of the separated flow region and to significantly decrease the profile losses caused by separation over a wide range of Reynolds numbers. These experiments were carried out in the High-Speed Cascade Wind Tunnel of the German Federal Armed Forces University Munich, Germany, which allows to capture the effects of pulsed blowing at engine relevant conditions. The assumed control mechanism was the triggering of boundary layer transition by excitation of the Tollmien-Schlichting waves. The current work aims to gain further insight into the effects of pulsed blowing. It investigates the effect of a highly efficient configuration of pulsed blowing at a frequency of 9.5 kHz on the boundary layer at a Reynolds number of 70000 and exit Mach number of 0.6. The boundary layer profiles were measured at five positions between peak Mach number and the trailing edge with hot wire anemometry and pneumatic probes. Experiments were conducted with and without actuation under steady as well as periodically unsteady inflow conditions. The results show the development of the boundary layer and its interaction with incoming wakes. It is shown that pulsed blowing accelerates transition over the separation bubble and drastically reduces the boundary layer thickness.

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