Pressure Surface Separations in Low-Pressure Turbines—Part 2: Interactions With the Secondary Flow

2002 ◽  
Vol 124 (3) ◽  
pp. 402-409 ◽  
Author(s):  
Michael J. Brear ◽  
Howard P. Hodson ◽  
Paloma Gonzalez ◽  
Neil W. Harvey
Keyword(s):  
Secondary Flow ◽  
Turbine Blades ◽  
Low Pressure ◽  
Secondary Flows ◽  
Suction Surface ◽  
Linear Cascade ◽  
Surface Separation ◽  
Pressure Surface ◽  
Low Pressure Turbine ◽  
Turbine Design

This paper describes a study of the interaction between the pressure surface separation and the secondary flow on low-pressure turbine blades. It is found that this interaction can significantly affect the strength of the secondary flow and the loss that it creates. Experimental and numerical techniques are used to study the secondary flow in a family of four low-pressure turbine blades in linear cascade. These blades are typical of current designs, share the same suction surface and pitch, but have differing pressure surfaces. A mechanism for the interaction between the pressure surface separation and the secondary flow is proposed and is used to explain the variations in the secondary flows of the four blades. This mechanism is based on simple dynamical secondary flow concepts and is similar to the aft-loading argument commonly used in modern turbine design.

Pressure Surface Separations in Low Pressure Turbines: Part 2 of 2 — Interactions With the Secondary Flow

2001 ◽  
Author(s):  
Michael J. Brear ◽  
Howard P. Hodson ◽  
Paloma Gonzalez ◽  
Neil W. Harvey
Keyword(s):  
Secondary Flow ◽  
Turbine Blades ◽  
Low Pressure ◽  
Secondary Flows ◽  
Suction Surface ◽  
Linear Cascade ◽  
Surface Separation ◽  
Pressure Surface ◽  
Low Pressure Turbine ◽  
Turbine Design

This paper describes a study of the interaction between the pressure surface separation and the secondary flow on low pressure turbine blades. It is found that this interaction can significantly affect the strength of the secondary flow and the loss that it creates. Experimental and numerical techniques are used to study the secondary flow in a family of four low pressure turbine blades in linear cascade. These blades are typical of current designs, share the same suction surface and pitch, but have differing pressure surfaces. A mechanism for the interaction between the pressure surface separation and the secondary flow is proposed and is used to explain the variations in the secondary flows of the four blades. This mechanism is based on simple dynamical secondary flow concepts and is similar to the aft-loading argument commonly used in modern turbine design.

Experimental Study of the Unsteady Aerodynamics in a Linear Cascade With Low Reynolds Number Low Pressure Turbine Blades

1997 ◽  
Author(s):  
Christopher G. Murawski ◽  
Rolf Sondergaard ◽  
Richard B. Rivir ◽  
Kambiz Vafai ◽  
Terrence W. Simon ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Turbulence Intensity ◽  
Turbine Blades ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Freestream Turbulence ◽  
Suction Surface ◽  
Linear Cascade ◽  
Low Pressure Turbine ◽  
Flow Reynolds Number

Low pressure turbines in aircraft experience large changes in flow Reynolds number as the gas turbine engine operates from takeoff to high altitude cruise. Low pressure turbine blades are also subject to regions of strong acceleration and diffusion. These changes in Reynolds number, strong acceleration, as well as elevated levels of turbulence can result in unsteady separation and transition zones on the surface of the blade. An experimental study was conducted in a two-dimensional linear cascade, focusing on the suction surface of a low pressure turbine blade. The intent was to assess the effects of changes in Reynolds number, and freestream turbulence intensity. Flow Reynolds numbers, based on exit velocity and suction surface length, have been varied from 50,000 to 300,000. The freestream turbulence intensity was varied from 1.1 to 8.1 percent. Separation was observed at all test Reynolds numbers. Increasing the flow Reynolds number, without changing freestream turbulence, resulted in a slightly rearward movement of the onset of separation and shrinkage of the separation zone. Increasing the freestream turbulence intensity, without changing Reynolds number resulted in a shrinkage of the separation region on the suction surface. Increasing both flow Reynolds numbers and freestream turbulence intensity compounded these effects such that at a Reynolds number of 300,000 and a freestream turbulence intensity of 8.1%, the separation zone was almost nonexistent. The influences on the blade’s wake from altering freestream turbulence and Reynolds number are also documented. The width of the wake and velocity defect rise with a decrease in either turbulence level or chord Reynolds number. Numerical simulations were performed in support of experimental results. The numerical results compare well qualitatively with the low freestream turbulence experimental cases.

Numerical Investigation of Contrasting Flow Physics in Different Zones of a High-Lift Low-Pressure Turbine Blade

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Jiahuan Cui ◽  
V. Nagabhushana Rao ◽  
Paul Tucker
Keyword(s):  
Boundary Layer ◽  
Turbine Blade ◽  
Low Pressure ◽  
The State ◽  
Suction Surface ◽  
Flow Physics ◽  
Pressure Surface ◽  
Low Pressure Turbine ◽  
Flow Features ◽  
The Impact

Using a range of high-fidelity large eddy simulations (LES), the contrasting flow physics on the suction surface, pressure surface, and endwalls of a low-pressure turbine (LPT) blade (T106A) was studied. The current paper attempts to provide an improved understanding of the flow physics over these three zones under the influence of different inflow boundary conditions. These include: (a) the effect of wakes at low and high turbulence intensity on the flow at midspan and (b) the impact of the state of the incoming boundary layer on endwall flow features. On the suction surface, the pressure fluctuations on the aft portion significantly reduced at high freestream turbulence (FST). The instantaneous flow features revealed that this reduction at high FST (HF) is due to the dominance of “streak-based” transition over the “Kelvin–Helmholtz” (KH) based transition. Also, the transition mechanisms observed over the turbine blade were largely similar to those on a flat plate subjected to pressure gradients. On pressure surface, elongated vortices were observed at low FST (LF). The possibility of the coexistence of both the Görtler instability and the severe straining of the wakes in the formation of these elongated vortices was suggested. While this was true for the cases under low turbulence levels, the elongated vortices vanished at higher levels of background turbulence. At endwalls, the effect of the state of the incoming boundary layer on flow features has been demonstrated. The loss cores corresponding to the passage vortex and trailing shed vortex were moved farther from the endwall with a turbulent boundary layer (TBL) when compared to an incoming laminar boundary layer (LBL). Multiple horse-shoe vortices, which constantly moved toward the leading edge due to a low-frequency unstable mechanism, were captured.

Large Eddy Simulation and CDNS Investigation of T106C Low-Pressure Turbine

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Site Hu ◽  
Chao Zhou ◽  
Zhenhua Xia ◽  
Shiyi Chen
Keyword(s):  
Large Eddy Simulation ◽  
Flow Separation ◽  
Separated Flow ◽  
Low Pressure ◽  
Secondary Flows ◽  
Computational Domain ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Eddy Simulation ◽  
Large Eddy

This study investigates the aerodynamic performance of a low-pressure turbine, namely the T106C, by large eddy simulation (LES) and coarse grid direct numerical simulation (CDNS) at a Reynolds number of 100,000. Existing experimental data were used to validate the computational fluid dynamics (CFD) tool. The effects of subgrid scale (SGS) models, mesh densities, computational domains and boundary conditions on the CFD predictions are studied. On the blade suction surface, a separation zone starts at a location of about 55% along the suction surface. The prediction of flow separation on the turbine blade is always found to be difficult and is one of the focuses of this work. The ability of Smagorinsky and wall-adapting local eddy viscosity (WALE) model in predicting the flow separation is compared. WALE model produces better predictions than the Smagorinsky model. CDNS produces very similar predictions to WALE model. With a finer mesh, the difference due to SGS models becomes smaller. The size of the computational domain is also important. At blade midspan, three-dimensional (3D) features of the separated flow have an effect on the downstream flows, especially for the area near the reattachment. By further considering the effects of endwall secondary flows, a better prediction of the flow separation near the blade midspan can be achieved. The effect of the endwall secondary flow on the blade suction surface separation at the midspan is explained with the analytical method based on the Biot–Savart Law.

Unsteady Flow in Oscillating Turbine Cascade: Part 1 — Linear Cascade Experiment

1996 ◽  
Author(s):  
L. He
Keyword(s):  
Computational Study ◽  
Separation Bubble ◽  
Turbine Blades ◽  
Leading Edge ◽  
Computational Method ◽  
Reattachment Point ◽  
Suction Surface ◽  
Linear Cascade ◽  
Unsteady Pressure ◽  
Pressure Surface

An experimental and computational study has been carried out on a linear cascade of low pressure turbine blades with the middle blade oscillating in a torsion mode. The main objectives of the present work were to enhance understanding of the behaviour of bubble type of flow separation and to examine the predictive ability of a computational method. In addition, an attempt was made to address a general modelling issue: was the linear assumption adequately valid for such kind of flow? In Part 1 of this paper, the experimental work was described. Unsteady pressure was measured along blade surfaces using off-board mounted pressure transducers at realistic reduced frequency conditions. A short separation bubble on the suction surface near the trailing edge and a long leading-edge separation bubble on the pressure surface were identified. It was found that in the regions of separation bubbles, unsteady pressure was largely influenced by the movement of reattachment point, featured by an abrupt phase shift and an amplitude trough in the 1st harmonic distribution. The short bubble on the suction surface seemed to follow closely a laminar bubble transition model in a quasi-steady manner, and had a localized effect. The leading-edge long bubble on the pressure surface, on the other hand, was featured by a large movement of the reattachment point, which affected the surface unsteady pressure distribution substantially. As far as the aerodynamic damping was concerned, there was a destabilizing effect in the separated flow region, which was however largely balanced by the stabilizing effect downstream of the reattachment point due to the abrupt phase change.

scholarly journals Secondary Flow Reduction in a Nozzle Guide Vane Cascade by Non-Axisymmetric End-Wall Profiling

1999 ◽  
Author(s):  
J. Yan ◽  
D. G. Gregory-Smith ◽  
P. J. Walker
Keyword(s):  
Secondary Flow ◽  
Static Pressure ◽  
Guide Vane ◽  
Suction Surface ◽  
Linear Cascade ◽  
Pressure Surface ◽  
Nozzle Guide Vane ◽  
Nozzle Guide ◽  
Nozzle Guide Vanes ◽  
End Wall

A linear cascade of HP steam turbine nozzle guide vanes was designed and built in order to study the effect of a non-axisymmetric profile for the endwall. The profile was designed by using CFD for the purpose of reducing the secondary flow. The method was to use convex curvature near the pressure surface to reduce the static pressure and concave curvature near the suction surface to increase it. Thus the cross passage pressure gradient which drives the secondary flow would be reduced. Detailed investigations of the flow field with a flat end-wall and the profiled end-wall were conducted. The effect of the profiled end-wall on the secondary flow development was determined and also compared with the CFD design predictions. It was found that the secondary loss and secondary kinetic energy were both reduced by about 20% with the shaped endwall, and a more uniform exit flow was also achieved.

Numerical Validations of Secondary Flows and Loss Development Downstream of a Highly Loaded Low Pressure Turbine Outlet Guide Vane Cascade

2007 ◽  
Author(s):  
Johan Hja¨rne ◽  
Valery Chernoray ◽  
Jonas Larsson ◽  
Lennart Lo¨fdahl
Keyword(s):  
Numerical Simulations ◽  
Secondary Flow ◽  
Incompressible Flows ◽  
Guide Vane ◽  
Low Pressure ◽  
Flow Fields ◽  
Secondary Flows ◽  
Test Facility ◽  
Low Pressure Turbine ◽  
Highly Loaded

In this paper 3D numerical simulations of turbulent incompressible flows are validated against experimental data from the linear low pressure turbine/outlet guide vane (LPT/OGV) cascade at Chalmers in Sweden. The validation focuses on the secondary flow-fields and loss developments downstream of a highly loaded OGV. The numerical simulations are performed for the same inlet conditions as in the test-facility with engine-like properties in terms of Reynolds number, boundary-layer thickness and inlet flow angles with the goal to validate how accurately and reliably the secondary flow fields and losses for both on- and off-design conditions can be predicted for OGV’s. Results from three different turbulence models as implemented in FLUENT, k-ε Realizable, kω-SST and the RSM are validated against detailed measurements. From these results it can be concluded that the RSM model predicts both the secondary flow field and the losses most accurately.

Tip Clearance Effects on Inlet Hot Streak Migration Characteristics in High Pressure Stage of a Vaneless Counter-Rotating Turbine

2009 ◽  
Vol 132 (1) ◽  
Author(s):  
Zhao Qingjun ◽  
Du Jianyi ◽  
Wang Huishe ◽  
Zhao Xiaolu ◽  
Xu Jianzhong
Keyword(s):  
High Pressure ◽  
Low Pressure ◽  
Turbine Rotor ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Suction Surface ◽  
Pressure Surface ◽  
Low Pressure Turbine ◽  
High Pressure Stage ◽  
Hot Streak

In this paper, three-dimensional multiblade row unsteady Navier–Stokes simulations at a hot streak temperature ratio of 2.0 have been performed to reveal the effects of rotor tip clearance on the inlet hot streak migration characteristics in high pressure stage of a vaneless counter-rotating turbine. The numerical results indicate that the migration characteristics of the hot streak in the high pressure turbine rotor are dominated by the combined effects of secondary flow, buoyancy, and leakage flow in the rotor tip clearance. The leakage flow trends to drive the hotter fluid toward the blade tip on the pressure surface and to the hub on the suction surface. Under the effect of the leakage flow, even partial hotter fluid near the pressure surface is also driven to the rotor suction surface through the tip clearance. Compared with the case without rotor tip clearance, the heat load of the high pressure turbine rotor is intensified due to the effects of the leakage flow. And the results indicate that the leakage flow effects trend to increase the low pressure turbine rotor inlet temperature at the tip region. The air flow with higher temperature at the tip region of the low pressure turbine rotor inlet will affect the flow and heat transfer characteristics in the downstream low pressure turbine.

Influence of the state of the inlet endwall boundary layer on the interaction between pressure surface separation and endwall flows

2003 ◽  
Vol 217 (4) ◽  
pp. 433-441 ◽  
Author(s):  
E. Rosa de la Blanco ◽  
H. P. Hodson ◽  
R Vazquez ◽  
D Torre
Keyword(s):  
Boundary Layer ◽  
Static Pressure ◽  
Separation Bubble ◽  
Turbine Blades ◽  
The State ◽  
Linear Cascade ◽  
Surface Separation ◽  
Pressure Surface ◽  
Passage Vortex ◽  
Lp Turbine

This paper describes the effect of the state of the inlet boundary layer (laminar or turbulent) on the structure of the endwall flow on two different profiles of low-pressure (LP) turbine blades (solid thin and hollow thick). At present the state of the endwall boundary layer at the inlet of a real LP turbine is not known. The intention of this paper is to show that, for different designs of LP turbine, the state of the inlet boundary layer affects the performance of the blade in very different ways. The testing was completed at low speed in a linear cascade using area traversing, flow visualization and static pressure measurements. The paper shows that, for a laminar inlet boundary layer the two profiles have a similar loss distribution and structure of endwall flow. However, for a turbulent inlet boundary layer the two profiles are shown to differ significantly in both the total loss and endwall flow structure. The pressure side separation bubble on the solid thin profile is shown to interact with the passage vortex, causing a higher endwall loss than that measured on the hollow thick profile.

The Influence of Different Endwall Contouring Locations on the Secondary Flow Losses in a Highly Loaded Low Pressure Turbine

2018 ◽  
Author(s):  
Wenhua Duan ◽  
Weiyang Qiao ◽  
Zuojun Wei ◽  
Jian Liu ◽  
Haoyi Cheng
Keyword(s):  
Secondary Flow ◽  
Separation Bubble ◽  
Three Dimensional ◽  
Leading Edge ◽  
Low Pressure ◽  
Suction Surface ◽  
Surface Separation ◽  
Flow Losses ◽  
Endwall Contouring ◽  
Highly Loaded

A detailed experimental and numerical investigation of the effect of endwall contouring on the secondary flow was performed in a highly loaded low pressure linear cascade. A comparison between a planar and three contoured configurations has been performed, and the three-dimensional endwall secondary flow structures and the secondary flow losses are here analyzed and discussed. For the contoured endwall, three locations of the same contouring were investigated, first one with the contouring starting upstream the airfoil and ending just before the leading edge of the airfoil, secondary one with the contouring starting upstream the airfoil and ending in the middle of the airfoil passage, the last one with the contouring starting just from the leading edge of the airfoil and continuing through the airfoil passage just ending at the trailing edge. The results suggest that the numerical results offer a reliable prediction for the endwall secondary flow structure together with suction surface separation bubble. It was found that all the three locations of contouring could reduce the secondary flow losses effectively. The location through the airfoil passage got the most benefit in the reduction of secondary flow losses whereas the all contouring upstream the airfoil location got the least. It was also found that the profile losses was affected by the contoured endwall.

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