scholarly journals Discussion: “The Unsteady Wake Interaction in Turbomachinery and Its Effect on Cavitation” (Yeh, Hsuan, and Eisenhuth, J. J., 1959, ASME J. Basic Eng., 81, pp. 181–188)

1959 ◽  
Vol 81 (2) ◽  
pp. 189
Author(s):  
R. X. Meyer
Keyword(s):  
Unsteady Wake ◽  
Wake Interaction

The Unsteady Wake Interaction in Turbomachinery and Its Effect on Cavitation

1959 ◽  
Vol 81 (2) ◽  
pp. 181-188 ◽  
Author(s):  
Hsuan Yeh ◽  
J. J. Eisenhuth
Keyword(s):  
General Trend ◽  
Substantial Agreement ◽  
Unsteady Wake ◽  
Wake Interaction ◽  
Blade Row ◽  
Theoretical Predictions ◽  
Predicted Values ◽  
Experimental Values ◽  
Pressure Perturbations ◽  
Theory And Experiments

This paper attempts first to predict theoretically the influence on the nonsteady pressure perturbations on a blade row as a result of periodic wakes shed from an upstream blade row, and then to compare such theoretical predictions with a series of carefully conducted cavitation experiments at the Garfield Thomas Water Tunnel of the Ordnance Research Laboratory. The results indicate that the experimental values of pressure perturbations are somewhat lower than theoretically predicted values. The general trend, e.g., the influence of wake width and wake spacing, is in substantial agreement between theory and experiments.

Circumferentially Non-Uniform Flow in the Rear Stage of a Multistage Compressor

2015 ◽  
Author(s):  
Simon Stummann ◽  
Peter Jeschke ◽  
Timo Metzler
Keyword(s):  
High Performance ◽  
Uniform Flow ◽  
Performance Measurements ◽  
Wake Interference ◽  
Unsteady Wake ◽  
Numerical Effort ◽  
Wake Interaction ◽  
Compressor Performance ◽  
Multistage Compressor ◽  
Main Effects

Full annulus midspan URANS simulations are performed to examine wake interaction for rows with different blade counts. The amount of non-uniform flow is studied particularly in the rear stages of a 3.5 stage compressor with a different blade count at all rows. A high-performance cluster was used for the required full annulus URANS simulations. Due to the high numerical effort, three representative operating points are investigated in quasi-3D. The simulations are performed at a midspan stream tube which take into consideration the contracting duct of the compressor. The results indicate two main effects: wake-wake interference and wake-airfoil interaction. Both effects are related to the particular clocking position, which affect each other accordingly. At the aerodynamic design point, non-uniform flow at the rear stage has a significant impact. Intensified unsteady wake-airfoil interaction near the surge line causes circumferential unequal flow separation. Close to choke, the shock strength depends on the Mach number, hence jet and wake inflow affects different losses. The frequently used assumption of periodic flow disregards the deviations shown. Based on the numerical results, the accuracy of performance measurements is presented. Non-uniform flow causes inaccuracy of more than one percentage point for stage and compressor performance measurements, which is more than commonly requested. In summary, interaction of rows with dissimilar blade count leads to non-uniform flow in rear stages that needs to be considered in performance measurements.

scholarly journals Vortex suppression and drag reduction in the wake of counter-rotating cylinders

2011 ◽  
Vol 679 ◽  
pp. 343-382 ◽  
Author(s):  
ANDRE S. CHAN ◽  
PETER A. DEWEY ◽  
ANTONY JAMESON ◽  
CHUNLEI LIANG ◽  
ALEXANDER J. SMITS
Keyword(s):  
Drag Reduction ◽  
Vortex Shedding ◽  
Rotation Rate ◽  
Reynolds Numbers ◽  
Instability Region ◽  
Complete Suppression ◽  
Rotating Cylinders ◽  
Critical Rotation ◽  
Unsteady Wake ◽  
Wake Interaction

The flow over a pair of counter-rotating cylinders is investigated numerically and experimentally. It is demonstrated that it is possible to suppress unsteady vortex shedding for gap sizes from one to five cylinder diameters, at Reynolds numbers from 100 to 200, expanding on the more limited work by Chan & Jameson (Intl J. Numer. Meth. Fluids, vol. 63, 2010, p. 22). The degree of unsteady wake suppression is proportional to the speed and the direction of rotation, and there is a critical rotation rate where a complete suppression of flow unsteadiness can be achieved. In the doublet-like configuration at higher rotational speeds, a virtual elliptic body that resembles a potential doublet is formed, and the drag is reduced to zero. The shape of the elliptic body primarily depends on the gap between the two cylinders and the speed of rotation. Prior to the formation of the elliptic body, a second instability region is observed, similar to that seen in studies of single rotating cylinders. It is also shown that the unsteady wake suppression can be achieved by rotating each cylinder in the opposite direction, that is, in a reverse doublet-like configuration. This tends to minimize the wake interaction of the cylinder pair and the second instability does not make an appearance over the range of speeds investigated here.

Unsteady Work Transfer Within a Turbine Blade Row Passage

2014 ◽  
Vol 136 (9) ◽  
Author(s):  
Martin G. Rose ◽  
Martin Marx
Keyword(s):  
Total Pressure ◽  
Static Pressure ◽  
Linear Solution ◽  
Turbine Efficiency ◽  
Reduced Frequency ◽  
Clear Explanation ◽  
Unsteady Wake ◽  
Wake Interaction ◽  
Governing Differential Equation ◽  
Axial Turbines

There is evidence in the literature of strong static pressure pulsation on the suction and pressure sides of turbine aerofoil rows experiencing unsteady wake interaction from upstream blade rows. This evidence is both computational and experimental. It has been proposed that this unsteady pulsation causes an unsteady work transfer between the wake and free-stream fluid. It has also been proposed that such a work transfer process may cause a reduction in downstream mixing losses and, thus, an improvement in turbine efficiency. While the literature has provided evidence of the existence of such pulsations, there is no clear explanation of why they occur. This paper addresses the above topic from an analytic perspective; a one-dimensional, incompressible, linear solution to the governing differential equation is used to shed light on this behavior. While the model lacks a lot of physical detail, the pulsation effect is captured, and it is shown that the unsteady pressure attenuates the amplitude of the unsteady total pressure through the transfer of work. The significance of reduced frequency is also clearly demonstrated with convection dominated flow at low reduced frequency and unsteady work dominated flow at high reduced frequencies. The model allows the specification of the amplitude and phase of the down stream static pressure perturbation. This variability is shown to have a significant effect on the attenuation of the unsteady total pressure. New insight is provided in to the much studied topic of “clocking” in axial turbines.

Unsteady Numerical Simulation of Shock Systems in Vaneless Counter-Rotating Turbine

2005 ◽  
Author(s):  
Huishe Wang ◽  
Qingjun Zhao ◽  
Xiaolu Zhao ◽  
Jianzhong Xu
Keyword(s):  
Numerical Simulation ◽  
Mach Number ◽  
Leading Edge ◽  
Turbine Rotor ◽  
Nozzle Design ◽  
Suction Surface ◽  
Rotor Wake ◽  
Wake Interaction ◽  
Unsteady Numerical Simulation ◽  
Almost All

A detailed unsteady numerical simulation has been carried out to investigate the shock systems in the high pressure (HP) turbine rotor and unsteady shock-wake interaction between coupled blade rows in a 1+1/2 counter-rotating turbine (VCRT). For the VCRT HP rotor, due to the convergent-divergent nozzle design, along almost all the span, fishtail shock systems appear after the trailing edge, where the pitch averaged relative Mach number is exceeding the value of 1.4 and up to 1.5 approximately (except the both endwalls). A group of pressure waves create from the suction surface after about 60% axial chord in the VCRT HP rotor, and those waves interact with the inner-extending shock (IES). IES first impinges on the next HP rotor suction surface and its echo wave is strong enough and cannot be neglected, then the echo wave interacts with the HP rotor wake. Strongly influenced by the HP rotor wake and LP rotor, the HP rotor outer-extending shock (OES) varies periodically when moving from one LP rotor leading edge to the next. In VCRT, the relative Mach numbers in front of IES and OES are not equal, and in front of IES, the maximum relative Mach number is more than 2.0, but in front of OES, the maximum relative Mach number is less than 1.9. Moreover, behind IES and OES, the flow is supersonic. Though the shocks are intensified in VCRT, the loss resulted in by the shocks is acceptable, and the HP rotor using convergent-divergent nozzle design can obtain major benefits.

The effect of tail geometry on the slipstream and unsteady wake structure of high-speed trains

2017 ◽  
Vol 83 ◽  
pp. 215-230 ◽  
Author(s):  
J.R. Bell ◽  
D. Burton ◽  
M.C. Thompson ◽  
A.H. Herbst ◽  
J. Sheridan
Keyword(s):  
High Speed ◽  
Wake Structure ◽  
Unsteady Wake ◽  
High Speed Trains
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