A Key Flow Parameter to the Profile Loss of Low-Pressure Turbine Blades

2021 ◽  
Author(s):  
Hidekazu Kodama ◽  
Ken-ichi Funazaki
Keyword(s):  
Boundary Layer ◽  
Performance Optimization ◽  
Flow Parameter ◽  
Friction Drag ◽  
Trailing Edge ◽  
Pressure Drag ◽  
Low Pressure Turbine ◽  
Flow Blockage ◽  
Profile Loss ◽  
Loss Level

Abstract For an optimum performance design of low-pressure turbine (LPT) blades, it is crucial to understand the generation mechanism of profile loss properly. As the profile loss is usually taken to be the loss generated inside the blade boundary layer due to viscous effects, most of the efforts for the performance optimization have concentrated on the reduction in the boundary layer loss using the flow parameters that represent the loss generation in the boundary layers. Kodama and Funazaki [1] investigated the generation mechanism of profile loss from a view point of blade drag forces, friction drag force and pressure drag force, and suggested that the loss due to pressure drag is dominant in the profile loss of a typical LPT blade. The loss due to pressure drag is not a boundary layer loss that is generated in the boundary layers, but a mixing loss that is generated downstream of the trailing edge. It is necessary to clarify a key flow parameter to the loss due to pressure drag for an effective performance optimization. This paper aims at investigating the flow parameter that is a measure of the profile loss. In the investigation, the profile loss is broken down into the loss components which are expressed by the boundary layer integral parameters at the trailing edge. Then the loss components are categorized into the loss due to friction drag or the loss due to pressure drag. The loss level of each component is evaluated by using the results of steady Reynolds Averaged Navier-Stokes (RANS) simulations to assess the contribution to the total profile loss. The evaluations are conducted for two kinds of blade profiles at three different Reynolds numbers. It is found that the largest contributor to the loss due to pressure drag, consequently to the total profile loss, is the loss associated with a mixing of accelerated free stream flow by the flow blockage at the trailing edge plane. The loss level is simply determined by the flow blockage. This suggests that the flow blockage at the trailing edge plane is the most important flow parameter for an optimum performance design of LPT blades.

Interpretation of Low-Pressure Turbine Profile Loss Generation Mechanisms From a Viewpoint of Blade Drag Forces

2020 ◽  
Author(s):  
Hidekazu Kodama ◽  
Ken-ichi Funazaki
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Separation Bubble ◽  
Friction Drag ◽  
Suction Surface ◽  
Pressure Drag ◽  
Low Pressure Turbine ◽  
Drag Forces ◽  
Wake Passing ◽  
Profile Loss

Abstract This paper describes the interpretation of a generation mechanism of profile loss of low pressure turbine (LPT) blades from a viewpoint of blade drag forces. On the analogy of profile drag of an isolated body, the profile loss of a cascade blade is subdivided into two components, the loss due to friction drag and the loss due to pressure drag. The friction drag is equal to the integral of all axial component of shearing stresses taken over the surface of the blade. The pressure drag, which does not exist in an inviscid flow, is due to the fact that the presence of the boundary later modifies the pressure distribution on the blade. The losses due to friction drag and pressure drag are evaluated for two kinds of blade profiles using the results of steady incompressible Reynolds Averaged Navier-Stokes (RANS) simulations at three different Reynolds numbers (Re), 57,000, 100,000 and 147,000. It is found that the trend of the total profile loss with Reynolds number is mainly determined by the trend of the loss due to pressure drag with Reynolds number. A rise in the total profile loss of the blade with a laminar separation bubble on the suction surface at low Reynolds number is mainly attributed to the increase in the pressure drag due to thickened suction surface boundary layer by the enlarged separation bubble. The friction drag and the pressure drag are also estimated for the measured data of low speed linear cascade tests with a moving-bar mechanism. In the estimation, the pressure drag is derived from the estimated total profile loss and the estimated friction drag by using boundary layer integral equations. It is found that the trend of total profile loss with incoming wake passing frequency is almost determined by the trend of the loss due to pressure drag with the wake passing frequency.

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.

Separated Flow Transition Under Simulated Low-Pressure Turbine Airfoil Conditions—Part 1: Mean Flow and Turbulence Statistics

2002 ◽  
Vol 124 (4) ◽  
pp. 645-655 ◽  
Author(s):  
Ralph J. Volino
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Shear Layer ◽  
Free Stream ◽  
Low Pressure ◽  
Turbulent Shear ◽  
Trailing Edge ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine ◽  
Turbulent Shear Stress

Boundary layer separation, transition and reattachment have been studied experimentally under low-pressure turbine airfoil conditions. Cases with Reynolds numbers (Re) ranging from 25,000 to 300,000 (based on suction surface length and exit velocity) have been considered at low (0.5%) and high (9% inlet) free-stream turbulence levels. Mean and fluctuating velocity and intermittency profiles are presented for streamwise locations all along the airfoil, and turbulent shear stress profiles are provided for the downstream region where separation and transition occur. Higher Re or free-stream turbulence level moves transition upstream. Transition is initiated in the shear layer over the separation bubble and leads to rapid boundary layer reattachment. At the lowest Re, transition did not occur before the trailing edge, and the boundary layer did not reattach. Turbulent shear stress levels can remain low in spite of high free-stream turbulence and high fluctuating streamwise velocity in the shear layer. The beginning of a significant rise in the turbulent shear stress signals the beginning of transition. A slight rise in the turbulent shear stress near the trailing edge was noted even in those cases which did not undergo transition or reattachment. The present results provide detailed documentation of the boundary layer and extend the existing database to lower Re. The present results also serve as a baseline for an investigation of turbulence spectra in Part 2 of the present paper, and for ongoing work involving transition and separation control.

Separated Flow Transition Under Simulated Low-Pressure Turbine Airfoil Conditions: Part 1 — Mean Flow and Turbulence Statistics

2002 ◽  
Author(s):  
Ralph J. Volino
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Shear Layer ◽  
Free Stream ◽  
Low Pressure ◽  
Turbulent Shear ◽  
Trailing Edge ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine ◽  
Turbulent Shear Stress

Boundary layer separation, transition and reattachment have been studied experimentally under low-pressure turbine airfoil conditions. Cases with Reynolds numbers (Re) ranging from 25,000 to 300,000 (based on suction surface length and exit velocity) have been considered at low (0.5%) and high (9% inlet) free-stream turbulence levels. Mean and fluctuating velocity and intermittency profiles are presented for streamwise locations all along the airfoil, and turbulent shear stress profiles are provided for the downstream region where separation and transition occur. Higher Re or free-stream turbulence level moves transition upstream. Transition is initiated in the shear layer over the separation bubble and leads to rapid boundary layer reattachment. At the lowest Re, transition did not occur before the trailing edge, and the boundary layer did not reattach. Turbulent shear stress levels can remain low in spite of high free-stream turbulence and high fluctuating streamwise velocity in the shear layer. The beginning of a significant rise in the turbulent shear stress signals the beginning of transition. A slight rise in the turbulent shear stress near the trailing edge was noted even in those cases which did not undergo transition or reattachment. The present results provide detailed documentation of the boundary layer and extend the existing database to lower Re. The present results also serve as a baseline for an investigation of turbulence spectra in Part 2 of the present paper, and for ongoing work involving transition and separation control.

The Effects of Trailing Edge Thickness on the Losses of Ultrahigh Lift Low Pressure Turbine Blades

2014 ◽  
Vol 136 (8) ◽  
Author(s):  
Chao Zhou ◽  
Howard Hodson ◽  
Christoph Himmel
Keyword(s):  
Turbine Blades ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Base Pressure ◽  
Manufacturing Cost ◽  
Surface Boundary ◽  
Trailing Edge ◽  
Low Pressure Turbine ◽  
Sst Model ◽  
Profile Loss

Experimental, numerical and analytical methods were used to investigate the effects of the blade trailing edge thickness on the profile loss of ultrahigh-lift low-pressure turbine blades. Two cascades, the T106C and the T2, were studied. The loss obtained based on the data at the blade trailing edge plane and the plane 0.3 Chord downstream of the trailing edge agree with each other for T106C blade with and without upstream wakes at different Reynolds numbers. The blade profile losses were broken down as the suction surface boundary loss, the pressure side boundary loss and the mixing loss downstream of the trailing edge for six Reynolds numbers. Trailing edge thicknesses varying from 1.4% to 4.7% pitch were investigated at a Reynolds number of 210,000. It was found that the flow distributions across the passage at the trailing edge planes were highly nonuniform. In particular, and as a result, the trailing edge base pressure was higher than the mixed-out static pressure, so the contribution of the base pressure to the mixing loss downstream of the trailing edge plane was to reduce the loss. When the trailing edge thickness increases, there are three main effects: (1) the area with high base pressure region increases, which tends to reduce the downstream mixing loss; (2) the base pressure reduces, which tends to increase the loss; and (3) the flow diffusion downstream of the trailing edge, which tends to increase the loss. The overall result is the combined effect. For the T106C cascade, increasing the trailing edge thickness from 1.9% pitch to 2.8% pitch has a small effect on the loss. Further increasing the trailing edge thickness increases the loss. The T2 blade has a higher lift than the T106C blade, so the effects of the base pressure in reducing the mixing loss downstream of the trailing edge is more evident. The experimental results show that the profile loss first decreases and then increases as the trailing edge thickness increases. CFD, using the transition k-ω SST model and the k-ω SST model, provides good predictions of the aerodynamic performance. It was used to study the cases with trailing edge thicknesses of 1.4% pitch and 2.9% pitch. The profile loss is almost the same for these two trailing edge thickness. The results show that it is possible to use thicker blade trailing edges in low pressure turbines without aerodynamic penalty. This can lead to benefits in terms of mechanical integrity and manufacturing cost reductions.

Reduction of friction drag by means of boundary layer laminarization using a dielectric barrier discharge

2012 ◽  
Vol 47 (4) ◽  
pp. 483-493
Author(s):  
M. N. Kogan ◽  
V. M. Litvinov ◽  
A. A. Uspenskii ◽  
M. V. Ustinov
Keyword(s):  
Boundary Layer ◽  
Dielectric Barrier Discharge ◽  
Barrier Discharge ◽  
Friction Drag ◽  
Dielectric Barrier

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.

Investigation of Aerodynamics and Heat Transfer of a Highly Loaded Turbine Blade Using the Universal Intermittency Function

2017 ◽  
Author(s):  
A. Nikparto ◽  
M. T. Schobeiri
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Gas Turbine ◽  
Flow Condition ◽  
Computational Results ◽  
Turbine Engine ◽  
Low Pressure Turbine ◽  
Unsteady Flow Condition ◽  
Highly Loaded

Efficiency and performance of gas turbine engines are affected by the flow field around the blades. The flow field inside a gas turbine engine is very complex. One of the characteristics of the flow inside an engine is existence of periodic unsteady wakes, originating from the upstream stator blades. The unsteady wakes, with their highly vortical core, impinge on the downstream blade surfaces and cause an intermittent transition of the flow regime from laminar to turbulent. This study aims at investigating and modeling the behavior and development of the boundary layer along the suction surface of a highly loaded low-pressure turbine blade under steady and unsteady inlet flow condition. The current paper includes results of a computational work substantiated by the experimental verifications. For the experimental investigations, the linear cascade facility in Turbomachinery Performance and Flow research Lab (TPFL) at Texas A&M University was used to simulate the periodic unsteady flow condition inside gas turbine engine. Moving wakes, originating from upstream blades, were simulated in this facility by moving rods attached to two parallel timing belts. Measurements and calculations were conducted at Reynolds number of 110,000. This Reynolds number pertains to cruise condition of a low-pressure turbine. At this Reynolds number, the flow around the blades is transitional and highly susceptible to flow separation. Aerodynamics experiments include measuring the boundary layer, locating its transition, separation and finally re-attachment using miniature hot wire probes. Heat transfer measurements along the suction and pressure surfaces were conducted utilizing a specially designed heat transfer blade that was instrumented with liquid crystal coating. To numerically simulate the transitional behavior of the boundary layer under periodic unsteady flow condition, a new intermittency function is developed which is based on the universal intermittency function developed by Chakka and Schobeiri [1]. Accurate prediction of the boundary layer behavior under the above conditions requires minimum and the maximum intermittency functions. These functions were developed inductively using the experimental results that were obtained in the absence of flow separation. In the current investigation the impact of the separation on the minimum and maximum intermittency are accounted for. The enhanced minimum and maximum intermittency functions along with the universal intermittency are implemented in a RANS based solver for computational simulation. The computational results are compared with (a) experimental ones and (b) with the computational results from RANS that involves Langtry-Menter [2, 3] method.

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