Investigation into Wake Interactions of Wind Lenses at Close Proximities

This investigation is aimed at an experimental determination of the unsteady flowfield downstream of a transonic high pressure turbine stage. The single stage measurements, which were part of a joined European project, were conducted in the windtunnel for rotating cascades of the DLR Go¨ttingen. Laser-2-focus (L2F) measurements were carried out in order to determine the Mach number, flow angle, and turbulence distributions. Furthermore, a fast response pitot probe was utilized to determine the total pressure distribution. The measurement position for both systems was 0.5 axial rotor chord downstream of the rotor trailing edge at midspan. While the measurement position remained fixed, the nozzle guide vane (NGV) was “clocked” to 12 positions covering one NGV pitch. The periodic fluctuations of the total pressure downstream of the turbine stage indicate that the NGV wake damps the total pressure fluctuations caused by the rotor wakes. Furthermore, the random fluctuations are significantly lower in the NGV wake affected region. Similar conclusions were drawn from the L2F turbulence data. Since the location of the interaction between NGV wake and rotor wake is determined by the NGV position, the described effects are potential causes for the benefits of “stator clocking” which have been observed by many researchers.

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A study of computational methods for wake structure and base pressure prediction of a generic SUV model with fixed and rotating wheels

Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering ◽

10.1177/0954407016685496 ◽

2017 ◽

Vol 231 (9) ◽

pp. 1222-1238 ◽

Cited By ~ 5

Author(s):

David Forbes ◽

Gary Page ◽

Martin Passmore ◽

Adrian Gaylard

Keyword(s):

Experimental Data ◽

Computational Methods ◽

Large Scale ◽

Ground Plane ◽

Computational Cost ◽

Rear Wheel ◽

Base Pressure ◽

Detached Eddy Simulation ◽

Wake Structure ◽

Wake Interactions

This study is an evaluation of the computational methods in reproducing experimental data for a generic sports utility vehicle (SUV) geometry and an assessment on the influence of fixed and rotating wheels for this geometry. Initially, comparisons are made in the wake structure and base pressures between several CFD codes and experimental data. It was shown that steady-state RANS methods are unsuitable for this geometry due to a large scale unsteadiness in the wake caused by separation at the sharp trailing edge and rear wheel wake interactions. unsteady RANS (URANS) offered no improvements in wake prediction despite a significant increase in computational cost. The detached-eddy simulation (DES) and Lattice–Boltzmann methods showed the best agreement with the experimental results in both the wake structure and base pressure, with LBM running in approximately a fifth of the time for DES. The study then continues by analysing the influence of rotating wheels and a moving ground plane over a fixed wheel and ground plane arrangement. The introduction of wheel rotation and a moving ground was shown to increase the base pressure and reduce the drag acting on the vehicle when compared to the fixed case. However, when compared to the experimental standoff case, variations in drag and lift coefficients were minimal but misleading, as significant variations to the surface pressures were present.

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The Effect of Vane Clocking on the Unsteady Flowfield in a One and a Half Stage Transonic Turbine

Volume 6: Turbo Expo 2007, Parts A and B ◽

10.1115/gt2007-27848 ◽

2007 ◽

Author(s):

O. Schennach ◽

R. Pecnik ◽

B. Paradiso ◽

E. Go¨ttlich ◽

A. Marn ◽

...

Keyword(s):

Laser Doppler Velocimetry ◽

Three Dimensional ◽

Fast Response ◽

Navier Stokes ◽

Doppler Velocimetry ◽

Pressure Transducers ◽

Wake Interactions ◽

Transonic Turbine ◽

Response Pressure ◽

Vane Clocking

The current paper presents the results of numerical and experimental clocking investigations performed in a high-pressure transonic turbine with a downstream vane row. The objective was a detailed analysis of shock and wake interactions in such a 1.5 stage machine while clocking the vanes. Therefore a transient 3D-Navier Stokes calculation was done for two clocking positions and the three dimensional results are compared with Laser-Doppler-Velocimetry measurements at midspan. Additionally the second vane was equipped with fast response pressure transducers to record the instantaneous surface pressure for 20 different clocking positions at midspan.

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Blade-Row Interactions in an LP Turbine at Design and Strong Off-Design Operation

Volume 2C: Turbomachinery ◽

10.1115/gt2014-25343 ◽

2014 ◽

Author(s):

Martin Lipfert ◽

Jan Habermann ◽

Martin G. Rose ◽

Stephan Staudacher ◽

Yavuz Guendogdu

Keyword(s):

Experimental Data ◽

Flow Field ◽

Three Dimensional ◽

Suction Side ◽

Test Facility ◽

Time Resolved ◽

Joint Project ◽

Multi Stage ◽

Blade Row ◽

Wake Interactions

In a joint project between the Institute of Aircraft Propulsion Systems (ILA) and MTU Aero Engines a two-stage low pressure turbine is tested at design and strong off-design conditions. The experimental data taken in the altitude test-facility aims to study the effect of positive and negative incidence of the second stator vane. A detailed insight and understanding of the blade row interactions at these regimes is sought. Steady and time-resolved pressure measurements on the airfoil as well as inlet and outlet hot-film traverses at identical Reynolds number are performed for the midspan streamline. The results are compared with unsteady multi-stage CFD predictions. Simulations agree well with the experimental data and allow detailed insights in the time-resolved flow-field. Airfoil pressure field responses are found to increase with positve incidence whereas at negative incidence the magnitude remains unchanged. Different pressure to suction side phasing is observed for the studied regimes. The assessment of unsteady blade forces reveals that changes in unsteady lift are minor compared to changes in axial force components. These increase with increasing positive incidence. The wake-interactions are predominating the blade responses in all regimes. For the positive incidence conditions vane 1 passage vortex fluid is involved in the midspan passage interaction leading to a more distorted three-dimensional flow field.

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Performance and wake characteristics of tidal turbines in an infinitely large array

Journal of Fluid Mechanics ◽

10.1017/jfm.2021.692 ◽

2021 ◽

Vol 925 ◽

Author(s):

Pablo Ouro ◽

Takafumi Nishino

Keyword(s):

Bulk Velocity ◽

Large Array ◽

Negative Effects ◽

Local Flow ◽

Flow Acceleration ◽

Positive Effects ◽

Tidal Turbines ◽

Macro Scale ◽

Wake Interactions ◽

Blockage Effect

The efficiency of tidal stream turbines in a large array depends on the balance between negative effects of turbine-wake interactions and positive effects of bypass-flow acceleration due to local blockage, both of which are functions of the layout of turbines. In this study we investigate the hydrodynamics of turbines in an infinitely large array with aligned or staggered layouts for a range of streamwise and lateral turbine spacing. First, we present a theoretical analysis based on an extension of the linear momentum actuator disc theory for perfectly aligned and staggered layouts, employing a hybrid inviscid-viscous approach to account for the local blockage effect within each row of turbines and the viscous (turbulent) wake mixing behind each row in a coupled manner. We then perform large-eddy simulation (LES) of open-channel flow for 28 layouts of tidal turbines using an actuator line method with doubly periodic boundary conditions. Both theoretical and LES results show that the efficiency of turbines (or the power of turbines for a given bulk velocity) in an aligned array decreases as we reduce the streamwise turbine spacing, whereas that in a staggered array remains high and may even increase due to the positive local blockage effect (causing the local flow velocity upstream of each turbine to exceed the bulk velocity) if the lateral turbine spacing is sufficiently small. The LES results further reveal that the amplitude of wake meandering tends to decrease as we reduce the lateral turbine spacing, which leads to a lower wake recovery rate in the near-wake region. These results will help to understand and improve the efficiency of tidal turbines in future large arrays, even though the performance of real tidal arrays may depend not only on turbine-to-turbine interactions within the array but also on macro-scale interactions between the array and natural tidal currents, the latter of which are outside the scope of this study.

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Computational Examination of Utility Scale Wind Turbine Wake Interactions

Journal of Fundamentals of Renewable Energy and Applications ◽

10.4172/2090-4541.1000174 ◽

2015 ◽

Vol 05 (04) ◽

Author(s):

Tyamo Okosun Chenn Q Zhou

Keyword(s):

Wind Turbine ◽

Wake Interactions ◽

Utility Scale ◽

Turbine Wake ◽

Wind Turbine Wake

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The Influence of Wake–Wake Interactions on Loss Fluctuations of a Downstream Axial Compressor Blade Row

Journal of Turbomachinery ◽

10.1115/1.2841780 ◽

1998 ◽

Vol 120 (4) ◽

pp. 695-704 ◽

Cited By ~ 6

Author(s):

G. J. Walker ◽

J. D. Hughes ◽

I. Ko¨hler ◽

W. J. Solomon

Keyword(s):

Free Stream ◽

Guide Vane ◽

Axial Compressor ◽

Inlet Guide Vane ◽

Viscous Losses ◽

Wake Interaction ◽

Blade Row ◽

Wake Interactions ◽

Periodic Fluctuations ◽

Disturbance Field

The interaction between wakes of an adjacent rotor–stator or stator–rotor blade row pair in an axial turbomachine is known to produce regular spatial variations in both the time-mean and unsteady flow fields in a frame relative to the upstream member of the pair. This paper examines the influence of such changes in the free-stream disturbance field on the viscous losses of a following blade row. Hot-wire measurements are carried out downstream of the outlet stator in a 1.5-stage axial compressor having equal blade numbers in the inlet guide vane (IGV) and stator rows. Clocking of the IGV row is used to vary the disturbance field experienced by the stator blades; the influence on stator wake properties is evaluated. The magnitude of periodic fluctuations in ensemble-averaged stator wake thickness is significantly influenced by IGV wake-rotor wake interaction effects. The changes in time-mean stator losses appear marginal.

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