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

2021 ◽  
pp. 1-12
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 = 200 000) in three cases of different endwall boundary layer conditions with and without periodically incoming wakes. The endwall boundary layer is characterized by 1DCTA measurements upstream of the blade passage. Secondary flow is evaluated by Five-hole-probemeasurements 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.

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.

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.

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.

On the Periodically Unsteady Interaction of Wakes, Secondary Flow Development, and Boundary Layer Flow in An Annular Low-Pressure Turbine Cascade: An Experimental Investigation

2019 ◽  
Vol 141 (9) ◽  
Author(s):  
Martin Sinkwitz ◽  
Benjamin Winhart ◽  
David Engelmann ◽  
Francesca di Mare ◽  
Ronald Mailach
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
Boundary Layer Flow ◽  
Measurement Data ◽  
Separated Flow ◽  
Low Pressure ◽  
Experimental Investigations ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Layer Flow

The experimental results reported in this contribution address the time-dependent impact of periodically unsteady wakes on the development of profile and end wall boundary layers and consequently on the secondary flow system. Experimental investigations are conducted on an annular 1.5 stage axial turbine rig at Ruhr-Universität Bochum’s Chair of Thermal Turbomachines and Aeroengines. The object under investigation is a modified T106 profile low-pressure turbine (LPT) stator row at a representative exit flow Reynolds number of 200,000. By making use of an annular geometry instead of a linear cascade, the influence of curvilinear end walls, nonuniform, increasing pitch across the span and radial flow migration can be represented. Incoming wakes are generated by a variable-speed driven rotor equipped with cylindrical bars. Special emphasis is put on the wake-induced recurrent formation, suppression, weakening, and displacement of individual vortices and separated flow regimes. For this, based on a comprehensive set of time-resolved measurement data, the interaction of impinging bar wakes and boundary layer flow and thus separation and its periodic manipulation along the passage end walls and on the blade suction surface are studied within the frequency domain.

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.

A Comparison of Turbulence Levels From Particle Image Velocimetry and Constant Temperature Anemometry Downstream of a Low-Pressure Turbine Cascade at High-Speed Flow Conditions

2020 ◽  
Vol 142 (7) ◽  
Author(s):  
Silvio Chemnitz ◽  
Reinhard Niehuis
Keyword(s):  
Particle Image Velocimetry ◽  
Constant Temperature ◽  
High Speed ◽  
Particle Image ◽  
Low Pressure ◽  
Operating Conditions ◽  
Stereoscopic Particle Image Velocimetry ◽  
Turbine Cascade ◽  
Low Pressure Turbine ◽  
Image Velocimetry

Abstract The development and verification of new turbulence models for Reynolds-averaged Navier–Stokes (RANS) equation-based numerical methods require reliable experimental data with a deep understanding of the underlying turbulence mechanisms. High accurate turbulence measurements are normally limited to simplified test cases under optimal experimental conditions. This work presents comprehensive three-dimensional data of turbulent flow quantities, comparing advanced constant temperature anemometry (CTA) and stereoscopic particle image velocimetry (PIV) methods under realistic test conditions. The experiments are conducted downstream of a linear, low-pressure turbine cascade at engine relevant high-speed operating conditions. The special combination of high subsonic Mach and low Reynolds number results in a low density test environment, challenging for all applied measurement techniques. Detailed discussions about influences affecting the measured result for each specific measuring technique are given. The presented time mean fields as well as total turbulence data demonstrate with an average deviation of ΔTu<0.4% and ΔC/Cref<0.9% an extraordinary good agreement between the results from the triple sensor hot-wire probe and the 2D3C-PIV setup. Most differences between PIV and CTA can be explained by the finite probe size and individual geometry.

Recognition of Structures Leading to Transition in a Low Pressure Turbine Cascade: Effect of Reduced Frequency

2019 ◽  
Author(s):  
D. Lengani ◽  
D. Simoni ◽  
M. Ubaldi ◽  
P. Zunino ◽  
F. Bertini
Keyword(s):  
Boundary Layer ◽  
Suction Side ◽  
Low Pressure ◽  
Turbine Cascade ◽  
Turbulent Structures ◽  
Time Resolved ◽  
Low Pressure Turbine ◽  
Reduced Frequency ◽  
Displacement Thickness ◽  
Wake Passing

Abstract The boundary layer developing over the suction side of a low pressure turbine cascade operating under unsteady inflow conditions has been experimentally investigated. Time-resolved Particle Image Velocimetry (PIV) measurements have been performed in two orthogonal planes, the blade to blade and a wall parallel plane embedded within the boundary layer, for two different wake reduced frequencies. Proper Orthogonal Decomposition (POD) has been used to analyze the data and to provide an interpretation of the most significant flow structures for each phase of the wake passing cycle. To this purpose, a POD based procedure that sorts the data synchronizing the measurements of the two planes has been developed. Phase averaged data are then obtained for both cases. Moreover, once properly sorted, POD has been applied to sub-ensembles of data at the same relative phase within the wake passing cycle. Detailed information on the most energetic turbulent structures at a particular phase are obtained with this procedure (called phased POD), overcoming the limit of classical phase average that just provides a statistical representation of the turbulence field. Furthermore, the synchronization of the measurements in the two planes allows the computation of the characteristic dimension of boundary layer structures that are responsible for transition. These structures are often identified as vortical filaments parallel to the wall, typically referred to as boundary layer streaks. The largest and most energetic structures are observed when the wake centerline passes over the rear part of the suction side, and they appear practically the same for both reduced frequencies. The passing wake forces transition leading to the breakdown of the boundary layer streaks. Otherwise, the largest differences between the low and high reduced frequency are observed in the calmed region. The post-processing of these two planes further allowed us to compute the spacing of the streaks and make it non-dimensional by the boundary layer displacement thickness observed for each phase. The non-dimensional value of the streaks spacing is about constant, irrespective of the reduced frequency.

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