Investigation of Low Solidity LP Turbine Cascade With Flow Control: Part 1—Active Flow Control Using Jet-Flap

2010 ◽  
Author(s):  
Ping-Ping Chen ◽  
Wei-Yang Qiao ◽  
Hua-Ling Luo ◽  
Farhan Ali Hashmi
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
Boundary Layer Separation ◽  
Turbine Cascade ◽  
Suction Surface ◽  
Layer Separation ◽  
Turbine Cascades ◽  
Lp Turbine ◽  
The Impact ◽  
Highly Loaded

Increasing the airfoil lift and decreasing the solidity of turbine cascade are the effective ways to decrease blade count which lead to the reduction of weight and hardware cost of gas turbine in aircraft engine. The challenge with this effort is to prevent the flow separation on blade suction surface and to keep the efficiency at high levels. Recent investigations on the blade-flap have demonstrated dramatic reduction in the separation losses of turbine. It would be very attractive to integrate the blade-flap in the design of enhanced loaded turbine. The critical science that will enable this design innovation is a comprehensive understanding of the effect of flow control device on the boundary layer separation. The purpose of the present work was to investigate the impact of turbine cascade solidity on loss mechanisms (airfoil lift level) and to study the feasibility to develop low solidity and highly loaded LP turbine cascade blade using blade flap. This paper is the Part I of the study concerned with performance improvement of low solidity and highly loaded LP turbine cascade blade with jet-flap. The Part II is concerned with the Gurney-flap. Investigation on three turbine cascades with same type of airfoil but different solidity is presented in this paper. These turbine cascades are all constructed with the P&W LPTs highly loaded airfoil Pack B. Two dimensional steady Reynolds-averaged Navier-Stokes equations are solved for the flow of these cascades. It is shown that appropriate jet flap could decrease turbine cascade solidity about 12.5% without the considerable increase in loss, the flow deflection of the turbine cascade mainstream can be increased by jet-flap, and then contribute to increased blade loading. Because of the augmented deflection of the cascade mainstream, the flow velocity at suction side of the adjacent blade increases. This results in extension of the flow accelerating region and reduction of flow diffusion on the blade suction surface, consequently there is a delay in the boundary layer separation and/or makes the reattachment point advanced. In fact, the neighboring blade boundary layer flow is affected by the deflection of the mainstream, not on the flow of local boundary directly.

Investigation of Low Solidity LP Turbine Cascade With Flow Control: Part 2—Passive Flow Control Using Gurney-Flap

2010 ◽  
Author(s):  
Ping-Ping Chen ◽  
Wei-Yang Qiao ◽  
Hua-Ling Luo
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
Separation Bubble ◽  
Suction Side ◽  
Boundary Layer Separation ◽  
Turbine Cascade ◽  
Passive Flow Control ◽  
Passive Flow ◽  
Gurney Flap ◽  
Lp Turbine

Numerical simulations were performed to investigate the effects of a passive flow control device named Gurney-flap on the laminar separation bubble and associated losses, aiming at assessing the feasibility of designing low solidity and highly-loaded LP turbine cascade with Gurney-flap. It was shown that with appropriate Gurney-flap the turbine cascade solidity could be decreased by 12.5% without loss increase. The deflection of the cascade mainstream due to Gurney flap can accelerate the flow at suction side of the adjacent blade, and decrease the adverse pressure gradient within the diffusion zone, which delay the boundary layer separation, thin the separation bubble and delay transition onset, contributing to reductions of both the separation-bubble-generated loss and the turbulent boundary-layer-generated loss. The numerical results indicate that the Gurney-flap height and type have significant impacts on the cascade performance, and the round Gurney-flap is the optimal flap type being the most effective for the reduction of flow losses.

A New Design Concept of Highly-Loaded Axial Flow Compressor by Applying Boundary Layer Suction and 3D Blade Technique

2008 ◽  
Author(s):  
Xiaoqing Qiang ◽  
Songtao Wang ◽  
Weichun Lin ◽  
Zhongqi Wang
Keyword(s):  
Boundary Layer ◽  
Pressure Ratio ◽  
Axial Flow ◽  
Boundary Layer Separation ◽  
Design Concept ◽  
Turning Angle ◽  
Boundary Layer Suction ◽  
Layer Separation ◽  
Flow Compressor ◽  
Highly Loaded

A new design concept of highly-loaded axial flow compressor by applying boundary layer suction and 3D blade technique was proposed in this paper. The basic idea of this design concept was that low reaction was adopted as while as increasing the rotor’s geometry turning angle, so that the boundary layer separation of a rotor could be eliminated and the rotor was kept working in high efficiency. This design concept would greatly increase the stator’s geometry turning angle, so boundary layer suction on stator cascades was adopted in order to restrain the boundary layer separation. In some situations, 3D blade technique was also applied in order to control the boundary layer separation more efficiently. The advantages of the above design concept were: the compressor’s pressure ratio was increased remarkably; boundary layer suction was only adopted in stator cascades so as to reduce the complexity of boundary layer suction structure. The key techniques of the new design concept were also explained in this paper. In order to increase the compressor’s pressure ratio, the geometry turning angle of rotor was increased greatly, and the rotor inlet was prewhirled to reduce the rotor’s reaction so as to restrain the rotor’s boundary separation. Boundary layer suction was carried out in the stator cascades (mainly on suction side), hub and shroud in order to control the flow separation. 3D blade technique could be adopted if necessary. The limitation of the application of this design concept was also pointed out through the analysis of the Mach number at rotor inlet, the prewhirl angle of rotor, the work distribution along span wise and the control method of stator separation. Numerical simulation was carried out on a single low-reaction compressor stage with IGV in order to demonstrate the new design concept. By using boundary layer suction and 3D blade technique, the energy loss in stator cascades was greatly reduced and the whole stage’s isentropic efficiency was about 90%. The low-reaction stage’s aerodynamic load was double than conventional design. The boundary layer separation could be effectively controlled by proper combination of boundary layer suction and bowed or twisted blade. The numerical result proved that the new design concept was feasible and had a wide application area.

Numerical Investigation of the Wake-Boundary Layer Interaction on a Highly Loaded LP Turbine Cascade Blade

2002 ◽  
Author(s):  
Pasquale Cardamone ◽  
Peter Stadtmu¨ller ◽  
Leonhard Fottner
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Transition Process ◽  
Reynolds Numbers ◽  
Numerical Approach ◽  
Experimental Investigations ◽  
Turbine Cascade ◽  
Suction Surface ◽  
Time Resolved ◽  
Highly Loaded

The effects of wake passing on the development of the profile boundary layer of a highly loaded low-pressure turbine cascade are studied using the RANS code TRACE-U. The numerical results are compared with available experimental data to verify the accuracy of the code in predicting the periodic-unsteady transition and separation mechanisms at low Reynolds number conditions. The experimental investigations have been carried out on a turbine cascade called T106D-EIZ subjected to wakes generated by an up-stream moving bar-type generator. The cascade pitch was increased by about 30% with respect to design conditions without modifying the blade geometry in order to obtain a large separation bubble on the suction surface. The extensive database containing time-averaged as well as time-resolved results was presented in a separate paper by Stadtmu¨ller and Fottner (2001) and is discussed only briefly. The time-accurate multistage Navier-Stokes solver TRACE-U developed by the DLR Cologne used for the numerical simulations employs a modified version of the one-equation Spalart-Allmaras turbulence model coupled with a transition correlation based on the work of Abu-Ghannam and Shaw in the formulation of Drela. The objective of this paper is to provide further insight into the aerodynamics of the wake-induced transition process and to rate the application limits of the numerical approach for exit Reynolds numbers as low as 60.000. The CFD predictions for two different flow conditions are compared with the measurements. Plots of wall-shear stress, blade loading, shape factor and loss behaviour are used to verify the reliability of the code. The periodic-unsteady development of the boundary layer as well as the loss behaviour is well reproduced for higher Reynolds numbers. For the case with massive separation, large discrepancies between numerical and experimental results are observed.

scholarly journals Blowing Snow as a Natural Glaciogenic Cloud Seeding Mechanism

2015 ◽  
Vol 143 (12) ◽  
pp. 5017-5033 ◽  
Author(s):  
Bart Geerts ◽  
Binod Pokharel ◽  
David A. R. Kristovich
Keyword(s):  
Boundary Layer ◽  
Weather Conditions ◽  
Boundary Layer Separation ◽  
Ice Crystals ◽  
Size Distributions ◽  
Blowing Snow ◽  
Free Atmosphere ◽  
Layer Separation ◽  
Orographic Clouds ◽  
The Impact

Abstract Winter storms are often accompanied by strong winds, especially over complex terrain. Under such conditions freshly fallen snow can be readily suspended. Most of that snow will be redistributed across the landscape (e.g., behind obstacles), but some may be lofted into the turbulent boundary layer, and even into the free atmosphere in areas of boundary layer separation near terrain crests, or in hydraulic jumps. Blowing snow ice crystals, mostly small fractured particles, thus may enhance snow growth in clouds. This may explain why shallow orographic clouds, with cloud-top temperatures too high for significant ice initiation, may produce (usually light) snowfall with remarkable persistence. While drifting snow has been studied extensively, the impact of blowing snow on precipitation on snowfall itself has not. Airborne radar and lidar data are presented to demonstrate the presence of blowing snow, boundary layer separation, and the glaciation of shallow supercooled orographic clouds. Further evidence for the presence of blowing snow comes from a comparison between snow size distributions measured at Storm Peak Laboratory (SPL) on Mount Werner (Colorado) versus those measured aboard an aircraft while passing overhead, and from an examination of snow size distributions at SPL under diverse weather conditions. Ice splintering following the collision of supercooled droplets on rimed surfaces such as trees does not appear to explain the large concentrations of small ice crystals sometimes observed at SPL.

Control of Highly Loaded Airfoil Boundary Layer Separation

2007 ◽  
Author(s):  
Augusto Lori ◽  
Mahmoud Ardebili ◽  
Yiannis Andreopoulos
Keyword(s):  
Boundary Layer ◽  
Delta Wing ◽  
Separated Flow ◽  
Boundary Layer Separation ◽  
Wall Region ◽  
High Momentum ◽  
Impulsive Motion ◽  
Delta Wings ◽  
Layer Separation ◽  
Highly Loaded

Control of boundary layer separation has been investigated employing micro-actuated delta winglets. The flow with the array is simulated computationally on two-dimensional airfoil boundary layer. The simulations capture vortices formed by the impulsive motion of the delta wings. The vortices are part of recirculating zone in the wake of the actuator, which as they advect downstream, bring high momentum fluid into the near wall region of a separated flow. Preliminary results indicate micro-actuated delta wing array affect boundary layer separation favorably.

Transient Performance of Separated Flows: Characterization and Active Flow Control

2018 ◽  
Author(s):  
J. Saavedra ◽  
G. Paniagua
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
Boundary Layer Separation ◽  
Low Pressure ◽  
Separated Flows ◽  
Shear Stresses ◽  
Recirculation Bubble ◽  
Control Approach ◽  
Layer Separation ◽  
Inlet Conditions

The aerothermal performance of the low pressure turbine in UAVs’ is significantly abated at high altitude, due to boundary layer separation. During past years different flow control strategies have been proposed to prevent boundary layer separation, such as dielectric barrier discharges, synthetic jets, vortex generators. However, the optimization of the control approach requires a better characterization of the separated regions at several frequencies. The present investigation analyzes the behavior of separated flows, and specifically reports the inception, reattachment and separation length, that allows the development of more efficient methods to manipulate flow separation under non-tempo-rally uniform inlet conditions. The development of separated flows under sudden flow accelerations or pulsating inlet conditions were investigated with series of numerical simulations including Unsteady Reynolds Average Navier Stokes and Large Eddy Simulations. The present research was performed on a wall mounted hump, which imposes an adverse pressure gradient representative of the suction side of low pressure turbines. The heat transfer and wall shear stresses were fully documented, as well as the flow velocity and temperature profiles at different axial locations to characterize the near wall flow properties and the thermal boundary layer. Through a sudden flow acceleration we looked into the dynamic response of the shear layer detachment as it is modulated by the mean flow evolution. Similarly, we studied the behavior of the recirculation bubble under periodic disturbances imposed by sinusoidal inlet total pressure signals at various frequencies ranging from 10 to 500 Hz. During each period the Reynolds number oscillates between 40000 and 180000 (based on a characteristic length of 0.1 m). Finally, as a first step into the flow control approach we added a slot in our geometry to allow flow injection and ingestion just upstream of the separation inception. Exploring the behavior of the separated region at different slot pressure conditions we defined the envelope for its periodic actuation. Thanks to that analysis, we found that matching the actuator frequency with the frequency response of the separated region the performance of the actuation is boosted.

Prediction of the Becalmed Region for LP Turbine Profile Design

1997 ◽  
Author(s):  
Volker Schulte ◽  
Howard P. Hodson
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Turbulent Flows ◽  
Laminar Boundary Layer ◽  
Turbine Blades ◽  
Boundary Layer Separation ◽  
Suction Surface ◽  
High Lift ◽  
Lp Turbine ◽  
Profile Loss

Recent attention has focused on the so called ‘becalmed region’ that is observed inside the boundary layers of turbomachinery blading and is associated with the process of wake-induced transition. Significant reductions of profile loss have been shown for high lift LP turbine blades at low Reynolds-numbers due the effects of the becalmed region on the diffusing flow at the rear of the suction surface. In this paper the nature and the significance of the becalmed region are examined using experimental observations and computational studies. It is shown that the becalmed region may be modelled using the unsteady laminar boundary layer equations. Therefore, it is predictable independently of the transition or turbulence models employed. The effect of the becalmed region on the transition process is modelled using a spot-based intermittency transition model. An unsteady differential boundary layer code was used to numerically simulate a deterministic experiment involving an isolated turbulent spot. The predictability of the becalmed region means that the rate of entropy production can be calculated in that region. It is found to be of the order of that in a laminar boundary layer. It is for this reason and because the becalmed region may be encroached upon by pursuing turbulent flows that for attached boundary layers, wake-induced transition cannot significantly reduce the profile loss. However, the becalmed region is less prone to separation than a conventional laminar boundary layer. Therefore, the becalmed region may be exploited in order to prevent boundary layer separation and the increase in loss that this entails. It is shown that it should now be possible to design efficient high lift LP turbine blades.

scholarly journals Analysis of the Effect of Vortex Generator Spacing on Boundary Layer Flow Separation Control

2019 ◽  
Vol 9 (24) ◽  
pp. 5495 ◽  
Author(s):  
Xin-kai Li ◽  
Wei Liu ◽  
Ting-jun Zhang ◽  
Pei-ming Wang ◽  
Xiao-dong Wang
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Kinetic Energy ◽  
Flow Control ◽  
Flow Separation ◽  
Lift Coefficient ◽  
Boundary Layer Separation ◽  
Wind Tunnel Experiments ◽  
Flow Separation Control ◽  
Layer Separation

During the operation of wind turbines, flow separation appears at the blade roots, which reduces the aerodynamic efficiency of the wind turbine. In order to effectively apply vortex generators (VGs) to blade flow control, the effect of the VG spacing (λ) on flow control is studied via numerical calculations and wind tunnel experiments. First, the large eddy simulation (LES) method was used to calculate the flow separation in the boundary layer of a flat plate under an adverse pressure gradient. The large-scale coherent structure of the boundary layer separation and its evolution process in the turbulent flow field were analyzed, and the effect of different VG spacings on suppressing the boundary layer separation were compared based on the distance between vortex cores, the fluid kinetic energy in the boundary layer, and the pressure loss coefficient. Then, the DU93-W-210 airfoil was taken as the research object, and wind tunnel experiments were performed to study the effect of the VG spacing on the lift–drag characteristics of the airfoil. It was found that when the VG spacing was λ/H = 5 (H represents the VG’s height), the distance between vortex cores and the vortex core radius were approximately equal, which was more beneficial for flow control. The fluid kinetic energy in the boundary layer was basically inversely proportional to the VG spacing. However, if the spacing was too small, the vortex was further away from the wall, which was not conducive to flow control. The wind tunnel experimental results demonstrated that the stall angle-of-attack (AoA) of the airfoil with the VGs increased by 10° compared to that of the airfoil without VGs. When the VG spacing was λ/H = 5, the maximum lift coefficient of the airfoil with VGs increased by 48.77% compared to that of the airfoil without VGs, the drag coefficient decreased by 83.28%, and the lift-to-drag ratio increased by 821.86%.

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.

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