scholarly journals Parasitic Loss Due to Leading Edge Instrumentation on a Low-Pressure Turbine Blade

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Henry C.-H. Ng ◽  
John D. Coull
Keyword(s):  
Boundary Layer ◽  
Aspect Ratio ◽  
Flow Behavior ◽  
Turbine Blades ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Low Pressure ◽  
Probe Diameter ◽  
Low Pressure Turbine ◽  
The Impact

During the testing of development engines and components, intrusive instrumentation such as Kiel-head pitot probes and shrouded thermocouples are used to evaluate gas properties and performance. The size of these instruments can be significant relative to the blades, and their impact on aerodynamic efficiency must be considered when analyzing the test data. This paper reports on such parasitic losses for instruments mounted on the leading edge of a stator in a low-pressure turbine, with particular emphasis on understanding the impact of probe geometry on the induced loss. The instrumentation and turbine blades have been modeled in a low Mach number cascade facility with an upstream turbulence grid. The cascade was designed so that the leading edge probes were interchangeable in situ, allowing for rapid testing of differing probe geometries. Reynolds-averaged Navier–Stokes (RANS) calculations were performed to complement the experiments and improve understanding of the flow behavior. A horseshoe vortex-like system forms at the join of the probe body and blade leading edge, generating pairs of streamwise vortices which convect over the blade pressure and suction surfaces. These vortices promote mixing between the freestream and boundary layer fluid and promote the transition of the boundary layer from laminar to turbulent flow. The size and shape of the leading edge probes relative to the blade vary significantly between applications. Tests with realistic probe geometries demonstrate that the detailed design of the shroud bleed system can impact the loss. A study of idealized cylinders is performed to isolate the impact of probe diameter, aspect ratio, and incidence. Beyond a probe aspect ratio of two, parasitic loss was found to scale approximately with probe frontal area.

scholarly journals Parasitic Loss due to Leading Edge Instrumentation on a Low Pressure Turbine Blade

2016 ◽  
Author(s):  
Henry C.-H. Ng ◽  
John D. Coull
Keyword(s):  
Boundary Layer ◽  
Turbine Blades ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Low Pressure ◽  
Probe Diameter ◽  
Low Pressure Turbine ◽  
And Performance ◽  
Pitot Probes ◽  
The Impact

During the testing of development engines and components, intrusive instrumentation such as Kiel head Pitot probes and shrouded thermocouples are used to evaluate gas properties and performance. The size of these instruments can be significant relative to the blades and their impact on aerodynamic efficiency must be considered when analysing the test data. This paper reports on such parasitic losses for instruments mounted on the leading edge of a stator in a low pressure turbine, with particular emphasis on understanding the impact of probe geometry on the induced loss. The instrumentation and turbine blades have been modeled in a low Mach number cascade facility with an upstream turbulence grid. The cascade was designed so that the leading edge probes were interchangeable in-situ, allowing for rapid testing of differing probe geometries. RANS calculations were performed to complement the experiments and gain more understanding about the flow behaviour. A horseshoe vortex-like system forms at the join of the probe body and blade leading edge, generating pairs of streamwise vortices which convect over the blade pressure and suction surfaces. These vortices promote mixing between the freestream and boundary layer fluid, and promote the transition of the boundary layer from laminar to turbulent flow. The size and shape of the leading edge probes relative to the blade varies significantly between applications. Tests with realistic probe geometries demonstrate that the detailed design of the shroud bleed system can impact the loss. A study of idealised cylinders is performed to isolate the impact of probe diameter, aspect ratio and incidence.

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.

Aerodynamic Effects of an Unshrouded Low Pressure Turbine on a Low Aspect Ratio Exit Guide Vane

2012 ◽  
Author(s):  
Thorsten Selic ◽  
Davide Lengani ◽  
Andreas Marn ◽  
Franz Heitmeir
Keyword(s):  
Aspect Ratio ◽  
Guide Vane ◽  
Low Pressure ◽  
Tip Clearance ◽  
Pressure Probe ◽  
Model Parameters ◽  
Leakage Flow ◽  
Low Pressure Turbine ◽  
Low Aspect Ratio ◽  
The Impact

This paper presents the effects of an unshrouded low pressure turbine (LPT) onto the following exit guide vane row (EGV). The measurement results were obtained in the subsonic test turbine facility at Graz University of Technology by means of a fast response pressure probe in planes downstream of the rotor as well as oil flow visualisation. The test rig was designed in cooperation with MTU Aero Engines and represents the last 1.5 stages of a commercial aero engine. Considerable efforts were put into the adjustment of all relevant model parameters to reproduce the full scale LPT situation. Different tip clearances were evaluated by means of CFD obtained using a commercial Navier-Stokes code and validated with experimental results. The goal is to evaluate the effect of the varying leakage flow on the flow in the low aspect ratio EGV. Special attention is given to the impact on the development of secondary flows as well as the flow structures downstream of the EGV. The effect of the leakage flow causes a change of the flow structure of the EGV, particularly losses. Considering the largest investigated tip-clearance, the losses increased by 71% when compared to a zero-leakage case.

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.

The effect of endwall boundary layer and incoming wakes on secondary flow in a high-lift low-pressure turbine cascade at low Reynolds number

2019 ◽  
Vol 233 (15) ◽  
pp. 5637-5649 ◽  
Author(s):  
Xiao Qu ◽  
Yanfeng Zhang ◽  
Xingen Lu ◽  
Zhijun Lei ◽  
Junqiang Zhu
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
High Lift ◽  
Low Pressure Turbine ◽  
Passage Vortex ◽  
Secondary Vortices

The endwall flow features are heavily dependent on the incoming boundary layer. It was particularly important to increase understanding the effect of inlet boundary layer thickness on endwall secondary flow under unsteady conditions. In present study, the influences of incoming wakes and various boundary layer thickness on endwall secondary flow were studied in a typical high-lift low-pressure turbine cascade, numerical calculation and experiment measurement of seven-hole probe were adopted at Re = 25,000 (based on the inlet velocity and the axial chord). Upstream wakes were simulated through moving rods upstream of the cascade. Detailed analysis was focused on the mechanisms of periodic wake influencing on the endwall vortex structures under thick endwall boundary layer condition. Influences of two different endwall boundary layer thickness on endwall secondary vortices structures were also comparatively analyzed. Under steady condition without wake, although thick incoming boundary layer reduces the cross-passage pressure gradient near endwall, more low momentum fluid inside thick endwall boundary layer is drawn into secondary vortices, finally resulting in stronger the pressure side leg of the leading edge horseshoe vortex and passage vortex, compared to the results of thin boundary layer condition. Under unsteady condition with thick inlet boundary layer, the “negative jet” effect of incoming wakes delays intersection of pressure side leg and suction side leg of leading edge horseshoe vortex on blade suction surface. The time-averaged strength of passage vortex and counter vortex core decreases by about 32%, and the underturning and overturning of endwall secondary flow is suppressed. The instantaneous results also indicate the endwall secondary vortices are reduced periodically at the position of wakes passing.

Characterization and Impact of Secondary Flows in a Discrete Passage Centrifugal Compressor Diffuser

2018 ◽  
Author(s):  
David W. Erickson ◽  
Choon S. Tan ◽  
Michael Macrorie
Keyword(s):  
Boundary Layer ◽  
Aspect Ratio ◽  
Centrifugal Compressor ◽  
Incidence Angle ◽  
Pressure Rise ◽  
Leading Edge ◽  
Layer Growth ◽  
Secondary Flows ◽  
The Impact ◽  
Boundary Layer Growth

Truncating the exit of a discrete passage centrifugal compressor diffuser is observed to enhance a research compressor’s stall line. By interrogating the experimental data along with a set of well-designed Reynolds-Averaged Navier Stokes computations, this improvement is traced to reduced impact of secondary flows on the truncated diffuser’s boundary layer growth. The secondary flow system is characterized by counter-rotating streamwise vortex pairs that persist throughout the diffuser passage. The vortices are traced to two sources: background vortices resulting from impeller exit flow non-uniformity, and incidence vortices resulting from flow separation off the leading edge cusps unique to a discrete passage diffuser. The incidence vortices detrimentally impact the diffuser pressure rise capability by accumulating high loss flow along the diffuser wall near the plane of symmetry between the vortices. This contributes to a large passage separation in the baseline diffuser. Using reduced order flow modeling, the impact of the vortices on the boundary layer growth is shown to scale inversely with diffuser aspect ratio, and thus the separation extent is reduced for the higher aspect ratio truncated diffuser. Because the diffuser incidence angle influences the strength and location of the vortices, this mechanism can affect the slope of the compressor’s pressure rise characteristic and impact its stall line. Stall onset for the baseline diffuser configuration is initiated by the transition of the vortex location and corresponding passage separation between diffuser pressure and suction sides with increased cusp incidence. Conversely, because the extent of the passage separation in the truncated diffuser is diminished, the switch in separation from pressure to suction side does not immediately initiate instability.

Low Pressure Turbine Relaminarization Bubble Characterization using Massively-Parallel Large Eddy Simulations

2012 ◽  
Vol 134 (2) ◽  
Author(s):  
Shriram Jagannathan ◽  
Markus Schwänen ◽  
Andrew Duggleby
Keyword(s):  
Boundary Layer ◽  
Reverse Flow ◽  
Leading Edge ◽  
Suction Side ◽  
Low Pressure ◽  
Surface Boundary ◽  
Suction Surface ◽  
Hairpin Vortices ◽  
Low Pressure Turbine ◽  
Large Eddy

The separation and reattachment of suction surface boundary layer in a low pressure turbine is characterized using large-eddy simulation at Ress = 69000 based on inlet velocity and suction surface length. Favorable comparisons are drawn with experiments using a high pass filtered Smagorinsky model for sub-grid scales. The onset of time mean separation is at s/so = 0.61 and reattachment at s/so = 0.81, extending over 20% of the suction surface. The boundary layer is convectively unstable with a maximum reverse flow velocity of about 13% of freestream. The breakdown to turbulence occurs over a very short distance of suction surface and is followed by reattachment. Turbulence near the bubble is further characterized using anisotropy invariant mapping and time orthogonal decomposition diagnostics. Particularly the vortex shedding and shear layer flapping phenomena are addressed. On the suction side, dominant hairpin structures near the transitional and turbulent flow regime are observed. The hairpin vortices are carried by the freestream even downstream of the trailing edge of the blade with a possibility of reaching the next stage. Longitudinal streaks that evolve from the breakdown of hairpin vortices formed near the leading edge are observed on the pressure surface.

Aerodynamics of leading-edge protection tapes for wind turbine blades

2020 ◽  
pp. 0309524X2097544
Author(s):  
Desirae Major ◽  
Jose Palacios ◽  
Mark Maughmer ◽  
Sven Schmitz
Keyword(s):  
Boundary Layer ◽  
Wind Turbine ◽  
Numerical Models ◽  
Turbine Blades ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Wind Turbine Blades ◽  
Layer Transition ◽  
Tape Edge ◽  
The Impact

This paper presents results of a comparative study on the effect of standard and tapered leading-edge protection (LEP) tapes on the annual energy production (AEP) of a utility-scale 1.5 MW wind turbine. Numerical models are developed in STAR-CCM+ to estimate the impact of LEP tapes on lift and drag coefficients of an NACA 64-618 airfoil operating at Re = 3 × 106. Experimental drag coefficient data are collected for LEP tapes applied to the tip-section of a de-commissioned wind turbine blade for numerical validation. The objective is to determine the physical mechanisms responsible for the aerodynamic degradation observed with standard LEP tapes, and to design a tapered LEP tape that reduces the associated adverse impact on AEP. An in-house wind turbine design and analysis code, XTurb-PSU, is used to estimate AEP using airfoil data obtained by STAR-CCM+. For standard LEP tapes, laminar-to-turbulent boundary-layer transition occurs at the LEP tape edge, resulting in AEP losses of 2%–3%. Comparable tapered LEP tapes can be designed to suppress boundary-layer transition for backward-facing step heights below a critical value such that associated impact on AEP is negligible.

Reynolds and Mach Number Effects on the Flow in a Low-Pressure Turbine

2020 ◽  
Author(s):  
Maxime Fiore
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Mach Number ◽  
Kinetic Energy ◽  
Gas Turbine ◽  
Guide Vane ◽  
Flow Behavior ◽  
Low Pressure ◽  
Secondary Flows ◽  
Low Pressure Turbine

Abstract This paper presents the Large Eddy Simulation (LES) of a Low-Pressure Turbine (LPT) Nozzle Guide Vane (NGV) for different Reynolds (Re) and Mach number (Ma). The analysis is based on a slice of the blade that may be representative of midspan flow where secondary flows, hub and shroud contributions are lower. In LPT, the variation of the Re during the mission of the gas turbine is a well-known effect since its value can vary of a factor four between take-off and cruise. This can induce performance variations due to various phenomena with among them suction side boundary layer separation on the aft portion of the blade due to an adverse pressure gradient and laminar boundary layer that can be maintained due to the relatively low Re in LPT. Similarly, the Ma in the LPT may vary depending on the thrust required from the gas turbine at the considered mission phase. The current paper investigates through numerical simulation the flow representative of a medium-sized LPT with three different Reynolds number Re = 175’000 (cruise), 280’000 (mid-level altitude) and 500’000 (take-off) keeping the same characteristic Mach number Ma = 0.2 and three different Mach number Ma = 0.2, 0.5 and 0.8 keeping the same Reynolds number Re = 280’000. The study focuses on different flow characteristics: pressure distribution around the blade, near-wall flow behavior and wake analysis. This includes the related generation of losses and the effect of Re and Ma on these different phenomena. A special emphasis is given to the generation of loss based on an entropy approach and the redistribution of mean kinetic energy towards turbulent kinetic energy. The results show that the increase of the Re has a destabilizing effect on potential separation while the increase of the Ma has a stabilizing effect. The peak in the TKE downstream of the blade is also moved upstream closer to the trailing edge when the Ma is increased.

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

2015 ◽  
Author(s):  
J. Cui ◽  
V. Nagabhushana Rao ◽  
P. G. 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, the contrasting flow physics on the suction surface, pressure surface and endwalls of a low pressure turbine 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 mid-span 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 Free-Stream Turbulence (FST). The instantaneous flow features revealed that this reduction at high FST is due to the dominance of ‘streak-based’ transition over the ‘Kelvin-Helmholtz’ 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. The possibility of the co-existence 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 when compared to an incoming laminar boundary layer. Multiple horse-shoe vortices, which constantly moved towards the leading edge due to a low-frequency unstable mechanism, were captured.

Sign in / Sign up

Export Citation Format

Share Document