Effects of Upstream Platform Geometry on the Endwall Flows of a Turbine Cascade

2005 ◽  
Author(s):  
Elena de la Rosa Blanco ◽  
H. P. Hodson ◽  
R. Va´zquez
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Turbine Cascade ◽  
Blade Profile ◽  
Linear Cascade ◽  
Surface Separation ◽  
Pressure Surface ◽  
Low Pressure Turbine ◽  
Large Pressure ◽  
Blade Row

This paper describes the effect that the endwall geometry has on the endwall flows in the vicinity of the blade platform in a low-pressure turbine. The aim of this work is to assess the effect on blade performance of a step in hub diameter just ahead of the blade row. The blade profile under consideration is of high aspect ratio and characterized by a large pressure surface separation bubble. The tests are conducted on a linear cascade and the experimental results are supported by numerical simulations. Two different steps are employed, i.e., forward facing and backward facing steps. Furthermore, the size of the step and the thickness of the inlet endwall boundary layer are also varied. It was found that the presence of the step ahead of the blade row can significantly alter the structure and the strength of the endwall flows. A backward facing step gives rise to lower losses when compared with a flat endwall. However, the effect is found to be dependent on the step height and the thickness of the approaching boundary layer. A forward facing step, on the other hand, produces higher losses than a flat endwall.

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.

Separated Flow Transition in a Low Pressure Turbine Cascade: Mean Flow and Turbulence Spectra

2003 ◽  
Author(s):  
Ralph J. Volino ◽  
Christopher G. Murawski
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Separation Bubble ◽  
Suction Side ◽  
Low Pressure ◽  
Turbine Cascade ◽  
Mean Flow ◽  
Turbulence Spectra ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine

Boundary layer separation, transition and reattachment have been studied experimentally in a low-pressure turbine cascade. Cases with Reynolds numbers (Re) ranging from 50,000 to 200,000 (based on suction surface length and exit velocity) have been considered under low free-stream turbulence conditions. Mean and fluctuating velocity profiles and turbulence spectra are presented for streamwise locations along the suction side of one airfoil and in the wake downstream of the airfoils. Hot film gages on the suction side surface of the airfoil are used to measure the fluctuation level and the spectra of the fluctuations on the surface. Higher Re moves transition upstream. Transition is initiated in the shear layer over the separation bubble and leads to boundary layer reattachment. Peak frequencies in the boundary layer spectra match those found in similar cases in the literature, indicating that the important frequencies may be predictable. Spectra in the wake downstream of the airfoils were similar to the spectra in the boundary layer near the trailing edge of the airfoil. Comparisons to the literature indicate that small but measurable differences in the spectra of the low free-stream turbulence can have a significant effect on boundary layer reattachment.

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.

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.

scholarly journals Prediction of Transient Pressure Fluctuations within a Low-Pressure Turbine Cascade Using a Lanczos-Filtered Harmonic Balance Method

2021 ◽  
Vol 6 (3) ◽  
pp. 25
Author(s):  
Jan Philipp Heners ◽  
Stephan Stotz ◽  
Annette Krosse ◽  
Detlef Korte ◽  
Maximilian Beck ◽  
...  
Keyword(s):  
Turbulence Model ◽  
Harmonic Balance ◽  
Separation Bubble ◽  
Pressure Fluctuations ◽  
Harmonic Balance Method ◽  
Low Pressure ◽  
Filter Method ◽  
Turbine Cascade ◽  
Transient Pressure ◽  
Low Pressure Turbine

Unsteady pressure fluctuations measured by fast-response pressure transducers mounted in a low-pressure turbine cascade are compared to unsteady simulation results. Three differing simulation approaches are considered, one time-integration method and two harmonic balance methods either resolving or averaging the time-dependent components within the turbulence model. The observations are used to evaluate the capability of the harmonic balance solver to predict the transient pressure fluctuations acting on the investigated stator surface. Wakes of an upstream rotor are generated by moving cylindrical bars at a prescribed rotational speed that refers to a frequency of f∼500 Hz. The excitation at the rear part of the suction side is essentially driven by the presence of a separation bubble and is therefore highly dependent on the unsteady behavior of turbulence. In order to increase the stability of the investigated harmonic balance solver, a developed Lanczos-type filter method is applied if the turbulence model is considered in an unsteady fashion.

Numerical Investigation of Loss Development in a Low-Pressure Turbine Cascade With Unsteady Inflow and Varying Inlet Endwall Boundary Layer

2021 ◽  
Author(s):  
Tobias Schubert ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Low Pressure ◽  
Turbine Cascade ◽  
Time Resolved ◽  
Blade Passage ◽  
Low Pressure Turbine ◽  
Wake Interaction ◽  
Spatial Redistribution ◽  
Unsteady Inflow ◽  
Flow Attenuation

Abstract An investigation of endwall loss development is conducted using the T106A low-pressure turbine cascade. (U)RANS simulations are complemented by measurements under engine relevant flow conditions (M2th = 0.59, Re2th = 2·105). The effects of unsteady inflow conditions and varying inlet endwall boundary layer are compared in terms of secondary flow attenuation downstream of the blade passage, analyzing steady, time-averaged, and time-resolved flow fields. While both measures show similar effects in the turbine exit plane, the upstream loss development throughout the blade passage is quite different. A variation of the endwall boundary layer alters the slope of the axial loss generation beginning around the midpoint of the blade passage. Periodically incoming wakes, however, cause a spatial redistribution of the loss generation with a premature loss increase due to wake interaction in the front part of the passage followed by an attenuation of the profile- and secondary loss generation in the aft section of the blade passage. Ultimately, this leads to a convergence of the downstream loss values in the steady and unsteady inflow cases.

Endwall Boundary Layer Development in an Engine Representative Four-Stage Low Pressure Turbine Rig

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Maria Vera ◽  
Elena de la Rosa Blanco ◽  
Howard Hodson ◽  
Raul Vazquez
Keyword(s):  
Boundary Layer ◽  
Leading Edge ◽  
Low Pressure ◽  
The State ◽  
Linear Cascade ◽  
Low Speed ◽  
Cold Flow ◽  
Low Pressure Turbine ◽  
Transitional Boundary Layer ◽  
Passage Vortex

Research by de la Rosa Blanco et al. (“Influence of the State of the Inlet Endwall Boundary Layer on the Interaction Between the Pressure Surface Separation and the Endwall Flows,” Proc. Inst. Mech. Eng., Part A, 217, pp. 433–441) in a linear cascade of low pressure turbine (LPT) blades has shown that the position and strength of the vortices forming the endwall flows depend on the state of the inlet endwall boundary layer, i.e., whether it is laminar or turbulent. This determines, amongst other effects, the location where the inlet boundary layer rolls up into a passage vortex, the amount of fluid that is entrained into the passage vortex, and the interaction of the vortex with the pressure side separation bubble. As a consequence, the mass-averaged stagnation pressure loss and therefore the design of a LPT depend on the state of the inlet endwall boundary layer. Unfortunately, the state of the boundary layer along the hub and casing under realistic engine conditions is not known. The results presented in this paper are taken from hot-film measurements performed on the casing of the fourth stage of the nozzle guide vanes of the cold flow affordable near term low emission (ANTLE) LPT rig. These results are compared with those from a low speed linear cascade of similar LPT blades. In the four-stage LPT rig, a transitional boundary layer has been found on the platforms upstream of the leading edge of the blades. The boundary layer is more turbulent near the leading edge of the blade and for higher Reynolds numbers. Within the passage, for both the cold flow four-stage rig and the low speed linear cascade, the new inlet boundary layer formed behind the pressure leg of the horseshoe vortex is a transitional boundary layer. The transition process progresses from the pressure to the suction surface of the passage in the direction of the secondary flow.

Effect of the Leakage Flows and the Upstream Platform Geometry on the Endwall Flows of a Turbine Cascade

2006 ◽  
Author(s):  
E. de la Rosa Blanco ◽  
H. P. Hodson ◽  
R. Vazquez
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Separation Bubble ◽  
Tangential Velocity ◽  
Low Pressure ◽  
Leakage Flow ◽  
Backward Facing Step ◽  
Surface Separation ◽  
Pressure Surface

This work describes the effect that the injection of leakage flow from a cavity into the mainstream has on the endwall flows and their interaction with a large pressure surface separation bubble in a low-pressure turbine. The effect of a step in hub diameter ahead of the blade row is also simulated. The blade profile under consideration is a typical design of modern low-pressure turbines. The tests are conducted in a low speed linear cascade. These are complemented by numerical simulations. Two different step geometries are investigated, i.e., a backward-facing step and a forward-facing step. The leakage tangential velocity and the leakage mass flow rate are also modified. It was found that the injection of leakage mass flow gives rise to a strengthening of the endwall flows independently of the leakage mass flow rate and the leakage tangential velocity. The experimental results have shown that below a critical value of the leakage tangential velocity, the net mixed-out endwall losses are not significantly altered by a change in the leakage tangential velocity. For these cases, the effect of the leakage mass flow is confined to the wall, as the inlet endwall boundary layer is pushed further away from the wall by the leakage flow. However, for values of the leakage tangential velocity around 100% of the wheelspeed, there is a large increase in losses due to a stronger interaction between the endwall flows and the leakage mass flow. This gives rise to a change in the endwall flows structure. In all cases, the presence of a forward-facing step produces a strengthening of the endwall flows and an increase of the net mixed-out endwall losses when compared with a backward-facing step. This is because of a strong interaction with the pressure surface separation bubble.

The Effects of Inlet Boundary Layer Condition and Periodically Incoming Wakes on Secondary Flow in a Low Pressure Turbine Cascade

2020 ◽  
Author(s):  
Tobias Schubert ◽  
Silvio Chemnitz ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
High Speed ◽  
Low Pressure ◽  
Experimental Investigations ◽  
Turbine Cascade ◽  
Flow Conditions ◽  
Low Pressure Turbine ◽  
Speed Flow ◽  
Unsteady Inflow

Abstract A particular turbine cascade design is presented with the goal of providing a basis for high quality investigations of endwall flow at high-speed flow conditions and unsteady inflow. The key feature of the design is an integrated two-part flat plate serving as a cascade endwall at part-span, which enables a variation of the inlet endwall boundary layer conditions. The new design is applied to the T106A low pressure turbine cascade for endwall flow investigations in the High-Speed Cascade Wind Tunnel of the Institute of Jet Propulsion at the Bundeswehr University Munich. Measurements are conducted at realistic flow conditions (M2th = 0.59, Re2th = 2·105) in three cases of different endwall boundary layer conditions with and without periodically incoming wakes. The endwall boundary layer is characterized by 1D-CTA measurements upstream of the blade passage. Secondary flow is evaluated by Five-hole-probe measurements in the turbine exit flow. A strong similarity is found between the time-averaged effects of unsteady inflow conditions and the effects of changing inlet endwall boundary layer conditions regarding the attenuation of secondary flow. Furthermore, the experimental investigations show, that all design goals for the improved T106A cascade are met.

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