Large Eddy Simulations of a Low-Pressure Turbine: Roughness Modeling and the Effects on Boundary Layer Transition and Losses

2018 ◽  
Author(s):  
F. Hammer ◽  
Neil D. Sandham ◽  
Richard D. Sandberg
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Low Pressure ◽  
Large Eddy Simulations ◽  
Boundary Layer Transition ◽  
Immersed Boundary ◽  
Spanwise Direction ◽  
Layer Transition ◽  
Low Pressure Turbine ◽  
Large Eddy

Large eddy simulations of a linear low-pressure turbine cascade with the T106A profile and different surface roughness patches were carried out. The aim was to investigate the effects on the laminar and turbulent boundary layer on the blade suction surface. Two different approaches were used to represent the roughness patches. Firstly, a forcing model, reducing the computational costs compared to fully resolved roughness surfaces, was incorporated. Secondly, an immersed boundary method representing an as-cast roughness surface was used, for a more detailed analysis of flow mechanisms over roughness. It was found that the roughness model was able to induce boundary layer transition and alter the turbulent boundary layer, with the results in line with findings in the literature. The instantaneous flow data at different time instants of the as-cast roughness case showed the development of streaks due to distinct roughness peaks, resulting in highly uneven transition positions across the spanwise direction.

The Effects of a Trip Wire and Unsteadiness on a High-Speed Highly Loaded Low-Pressure Turbine Blade

2004 ◽  
Vol 127 (4) ◽  
pp. 747-754 ◽  
Author(s):  
M. Vera ◽  
H. P. Hodson ◽  
R. Vazquez
Keyword(s):  
Boundary Layer ◽  
High Speed ◽  
Low Pressure ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Low Pressure Turbine ◽  
Roughness Elements ◽  
Unsteady Inflow ◽  
Mach Numbers ◽  
Inflow Conditions

This paper presents the effect of a single spanwise two-dimensional wire upon the downstream position of boundary layer transition under steady and unsteady inflow conditions. The study is carried out on a high turning, high-speed, low pressure turbine (LPT) profile designed to take account of the unsteady flow conditions. The experiments were carried out in a transonic cascade wind tunnel to which a rotating bar system had been added. The range of Reynolds and Mach numbers studied includes realistic LPT engine conditions and extends up to the transonic regime. Losses are measured to quantify the influence of the roughness with and without wake passing. Time resolved measurements such as hot wire boundary layer surveys and surface unsteady pressure are used to explain the state of the boundary layer. The results suggest that the effect of roughness on boundary layer transition is a stability governed phenomena, even at high Mach numbers. The combination of the effect of the roughness elements with the inviscid Kelvin–Helmholtz instability responsible for the rolling up of the separated shear layer (Stieger, R. D., 2002, Ph.D. thesis, Cambridge University) is also examined. Wake traverses using pneumatic probes downstream of the cascade reveal that the use of roughness elements reduces the profile losses up to exit Mach numbers of 0.8. This occurs with both steady and unsteady inflow conditions.

The Effects of a Trip Wire and Unsteadiness on a High Speed Highly Loaded Low-Pressure Turbine Blade

2004 ◽  
Author(s):  
M. Vera ◽  
H. P. Hodson ◽  
R. Vazquez
Keyword(s):  
Boundary Layer ◽  
High Speed ◽  
Low Pressure ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Low Pressure Turbine ◽  
Roughness Elements ◽  
Unsteady Inflow ◽  
Mach Numbers ◽  
Inflow Conditions

This paper presents the effect of a single spanwise 2D wire upon the downstream position of boundary layer transition under steady and unsteady inflow conditions. The study is carried out on a high turning, high-speed, low pressure turbine (LPT) profile designed to take account of the unsteady flow conditions. The experiments were carried out in a transonic cascade wind tunnel to which a rotating bar system had been added. The range of Reynolds and Mach numbers studied includes realistic LPT engine conditions and extends up to the transonic regime. Losses are measured to quantify the influence of the roughness with and without wake passing. Time resolved measurements such as hot wire boundary layer surveys and surface unsteady pressure are used to explain the state of the boundary layer. The results suggest that the effect of roughness on boundary layer transition is a stability governed phenomena, even at high Mach numbers. The combination of the effect of the roughness elements with the inviscid Kelvin-Helmholtz instability responsible for the rolling up of the separated shear layer (Stieger [1]) is also examined. Wake traverses using pneumatic probes downstream of the cascade reveal that the use of roughness elements reduces the profile losses up to exit Mach numbers of 0.8. This occurs with both steady and unsteady inflow conditions.

scholarly journals Description of the Flow in a Two-Stage Low-Pressure Turbine With Hub Cavities

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Maxime Fiore ◽  
Nicolas Gourdain ◽  
Jean-François Boussuge ◽  
Eric Lippinois
Keyword(s):  
Boundary Layer ◽  
Gas Turbine ◽  
Low Pressure ◽  
Secondary Flows ◽  
Boundary Layer Transition ◽  
Two Stage ◽  
Layer Transition ◽  
Low Pressure Turbine ◽  
Aspect Ratios ◽  
Multi Stage

Abstract In gas turbine, multi-stage row blading and technological effects can exhibit significant differences for the flow compared with isolated smooth blade rows. Upstream stages promote a non-uniform flow field at the inlet of the downstream rows that may have large effects on mixing or boundary layer transition processes. The rows of current turbines (and compressors) are already very closely spaced. Axial gaps between adjacent rows of approximately 1/4 to 1/2 of the axial blade chord are common practice. Future designs with higher loading and lower aspect ratios, i.e., fewer and bigger blades, and the ever present aim at minimizing engine length or compactness, will aggravate this condition even further. Interaction between cascade rows will therefore keep increasing and need to be taken into account in loss generation estimation. Also the cavities at hub platform induce purge flow blowing into main annulus and additional losses for the turbine. A robust method to account for the loss generated due to these different phenomena needs to be used. The notion of exergy (energy in the purpose to generate work) provides a general framework to deal with the different transfers of energy between the flow and the gas turbine. This study investigates the flow in a two-stage configuration representative of a low-pressure turbine including hub cavities based on large eddy simulation (LES). A description of the flow in the cavities, the main annulus, and at rim seal interface is proposed. The assessment of loss generated in the configuration is proposed based on an exergy analysis. The study of losses restricted to boundary layer contributions and secondary flows show the interaction processes of secondary vortices and wake generated in upstream rows on the flow in downstream rows.

Modelling Vortex Generating Jet-Induced Transition in Low-Pressure Turbines

2013 ◽  
Author(s):  
Florian Herbst ◽  
Andreas Fiala ◽  
Joerg R. Seume
Keyword(s):  
Boundary Layer ◽  
Cross Flow ◽  
Transition Process ◽  
Low Pressure ◽  
Boundary Layer Transition ◽  
Quantitative Prediction ◽  
Design Parameters ◽  
Transition Model ◽  
Layer Transition ◽  
Wall Flows

The current design of low-pressure turbines (LPTs) with steady-blowing vortex generating jets (VGJ) uses steady computational fluid dynamics (CFD). The present work aims to support this design approach by proposing a new semi-empirical transition model for injection-induced laminar-turbulent boundary layer transition. It is based on the detection of cross-flow vortices in the boundary layer which cause inflectional cross-flow velocity profiles. The model is implemented in the CFD code TRACE within the framework of the γ-Reθ transition model and is a reformulated, re-calibrated, and extended version of a previously presented model. It is extensively validated by means of VGJ as well as non-VGJ test cases capturing the local transition process in a physically reasonable way. Quantitative aerodynamic design parameters of several VGJ configurations including steady and periodic-unsteady inflow conditions are predicted in good accordance with experimental values. Furthermore, the quantitative prediction of end-wall flows of LPTs is improved by detecting typical secondary flow structures. For the first time, the newly derived model allows the quantitative design and optimization of LPTs with VGJs.

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