scholarly journals Numerical Investigation of the Cavitation Effects on the Vortex Shedding from a Hydrofoil with Blunt Trailing Edge

Fluids ◽  
2020 ◽  
Vol 5 (4) ◽  
pp. 218
Author(s):  
Jian Chen ◽  
Linlin Geng ◽  
Xavier Escaler
Keyword(s):  
Numerical Investigation ◽  
Vortex Shedding ◽  
Reference Frames ◽  
Vortex Formation ◽  
Wake Flow ◽  
Trailing Edge ◽  
Hydraulic Machinery ◽  
Laminar To Turbulent Transition ◽  
Blunt Trailing Edge ◽  
Shedding Frequency

Vortex cavitation can appear in the wake flow of hydrofoils, inducing unwanted consequences such as vibrations or unstable behaviors in hydraulic machinery and systems. To investigate the cavitation effects on hydrofoil vortex shedding, a numerical investigation of the flow around a 2D NACA0009 with a blunt trailing edge at free caviation conditions and at two degrees of cavitation developments has been carried out by means of the Zwart cavitation model and the LES WALE turbulence model which permits predicting the laminar to turbulent transition of the boundary layers. To analyze the dynamic behavior of the vortex shedding process and the coherent structures, two identification methods based on the Eulerian and Lagrangian reference frames have been applied to the simulated unsteady flow field. It is found that the cavitation occurrence in the wake significantly changes the main vortex shedding characteristics including the morphology of the vortices, the vortex formation length, the effective height of the near wake flow and the shedding frequency. The numerical results predict that the circular shape of the vortices changes to an elliptical one and that the vortex shedding frequency is significantly increased under cavitation conditions. The main reason for the frequency increase seems to be the reduction in the transverse separation between the upper and lower rows of vortices induced by the increase in the vortex formation length.

Wake Flow Behind a Cylinder With a Detached Splitter Plate

2005 ◽  
Author(s):  
Minter Cheng
Keyword(s):  
Strouhal Number ◽  
Vortex Shedding ◽  
Formation Process ◽  
Vortex Formation ◽  
Splitter Plate ◽  
Wake Flow ◽  
Plate Length ◽  
Splitter Plates ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

Fluid flow across a bluff body can induce a series alternating vortices in the downstream flow field. The vortex flow can produce adverse effects on many engineering applications. A number of studies have shown that the wake splitter plate is one of the means to stabilize the vortex formation process. However, most of the previous studies are confined to cylinders with attached splitter plates. Very few studies investigate the effects of the spacing between the cylinder and the splitter plate on the formation of wake vortices. In the present study, the effects of the splitter plate length as well as the gap distance between the splitter plate and the cylinder on the wake flow behind a cylinder have been studied experimentally for low Reynolds number of 400. Both circular and square cylinders are studied in this research. Four splitter plates with different length, 1 ≤ L/D ≤ 4, have been used and a range of cylinder and splitter plate gap distance, 0 < G/D < 6, have been studied. By using flow visualization technique and hot-film anemometer measurement, detailed measurements of the velocity distribution, the vortex shedding frequency, the wake width, and the wake formation length are carried out in order to get a clear understanding of the flow interference behavior. The experimental results indicate that splitter plates alter the vortex formation process in the wake causing a decrease in vortex shedding frequency. The Strouhal number decreases with increasing the splitter plate length as well as the gap distance between the cylinder and the splitter plate. It is shown that a jump in Strouhal number occurs at G/D of 3 to 6. The jump is splitter plate length dependent, and generally the gap distance at which jump takes place increases as the splitter plate length increases.

A study of three-dimensional aspects of vortex shedding from a bluff body with a mild geometric disturbance

1997 ◽  
Vol 330 ◽  
pp. 85-112 ◽  
Author(s):  
N. TOMBAZIS ◽  
P. W. BEARMAN
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Bluff Body ◽  
Vortex Formation ◽  
Three Dimensional ◽  
Base Pressure ◽  
Trailing Edge ◽  
Blunt Trailing Edge ◽  
Trailing Edges ◽  
Mode Transitions

Experiments have been carried out to study the three-dimensional characteristics of vortex shedding from a half-ellipse shape with a blunt trailing edge. In order to control the occurrence of vortex dislocations, the trailing edges of the models used were constructed with a series of periodic waves across their spans. Flow visualization was carried out in a water tunnel at a Reynolds number of 2500, based on trailing-edge thickness. A number of shedding modes were observed and the sequence of mode transitions recorded. Quantitative data were obtained from wind tunnel measurements performed at a Reynolds number of 40000. Two shedding frequencies were recorded with the higher frequency occurring at spanwise positions coinciding with minima in the chord. At these same positions the base pressure was lowest and the vortex formation length longest. Arguments are put forward to explain these observations. It is shown that the concept of a universal Strouhal number holds, even when the flow is three-dimensional. The spanwise variation in time-average base pressure is predicted using the estimated amount of time the flow spends at the two shedding frequencies.

The effect of base bleed on vortex shedding and base pressure in compressible flow

1981 ◽  
Vol 110 ◽  
pp. 273-292 ◽  
Author(s):  
F. Motallebi ◽  
J. F. Norbury
Keyword(s):  
Supersonic Flow ◽  
Compressible Flow ◽  
Vortex Shedding ◽  
Transonic Flow ◽  
Vortex Formation ◽  
Base Pressure ◽  
Trailing Edge ◽  
Blunt Trailing Edge ◽  
Base Bleed ◽  
The Relationship

Experiments have been carried out to investigate the phenomenon of vortex shedding from the blunt trailing edge of an aerodynamic body in transonic and supersonic flow. The effect of a discharge of bleed air from a slot in the trailing edge has been included and the relationship between the vortex formation and base pressure has been considered.In transonic flow a small amount of bleed air was found to produce a rearward shift in the point of origin of the vortices with a consequent substantial increase in base pressure. The effect was less marked in supersonic flow. At higher rates of bleed two different regimes of vortex shedding were identified and increase in bleed rate caused a reduction in base pressure. For bleed rates giving near-maximum base pressure no vortex shedding occurred.

scholarly journals Vortex shedding from a blunt trailing edge with equal and unequal external mean velocities

1976 ◽  
Vol 75 (4) ◽  
pp. 721-735 ◽  
Author(s):  
D. R. Boldman ◽  
P. F. Brinich ◽  
M. E. Goldstein
Keyword(s):  
Steady State ◽  
Flow Visualization ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Free Stream ◽  
Theoretical Calculations ◽  
Vortex Formation ◽  
Trailing Edge ◽  
Blunt Trailing Edge ◽  
Good Agreement

A flow-visualization study has shown that strong Kármán vortices develop behind the blunt trailing edge of a plate when the free-stream velocities over both surfaces are equal and that the vortices tend to disappear when the surface velocities are unequal. This observation provides an explanation for the occurrence and disappearance of certain discrete tones often found to be present in the noise spectra of coaxial jets. Both the vortex formation and the tones occur at a Strouhal number based on the lip thickness and the average of the external steady-state velocities of about 0.2.Results from theoretical calculations of the vortex formation, based on an inviscid incompressible analysis of the motion of point vortices, were in good agreement with the experimental observations.

scholarly journals Numerical Simulation on Vortex Shedding from a Hydrofoil in Steady Flow

2020 ◽  
Vol 8 (3) ◽  
pp. 195
Author(s):  
Jian Hu ◽  
Zibin Wang ◽  
Wang Zhao ◽  
Shili Sun ◽  
Cong Sun ◽  
...  
Keyword(s):  
Strouhal Number ◽  
Vortex Shedding ◽  
Angle Of Attack ◽  
Wake Flow ◽  
Trailing Edge ◽  
Inflow Velocity ◽  
Lift Curve ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Lift And Drag

This paper presents a numerical modeling procedure for the idealization of vortex shedding effects in the wake flow field of a NACA0009 hydrofoil. During the simulation, the lift and drag acting on the hydrofoil were monitored, and the vortex-shedding frequency of the hydrofoil was analyzed. The effects of inflow velocity, trailing-edge thickness, angle of attack, and maximum hydrofoil thickness on vortex shedding were investigated. The results indicate that an increase in the inflow velocity led to an increase in the vortex-shedding frequency and a negligible change in the Strouhal number. Furthermore, as the thickness of the trailing edge increased, the vortex-shedding frequency decreased gradually, whereas the Strouhal number first increased and then decreased. Vortex shedding and lift curve oscillations ceased altogether after the angle of attack of the hydrofoil increased beyond a certain threshold. When the maximum hydrofoil thickness was increased while keeping the thickness and chord length of the trailing edge constant, the vortex-shedding frequency decreased.

The near-wake of an oscillating trailing edge: mechanisms of periodic and aperiodic response

1993 ◽  
Vol 251 ◽  
pp. 173-201 ◽  
Author(s):  
A. Lotfy ◽  
D. Rockwell
Keyword(s):  
Vortex Formation ◽  
Wake Flow ◽  
Near Wake ◽  
Trailing Edge ◽  
Vortex Pattern ◽  
Blunt Trailing Edge ◽  
Topological Features ◽  
Unsteady Wake ◽  
The Times ◽  
Number Of Cycles

This investigation addresses the unsteady wake from a blunt trailing edge subjected to controlled perturbations. The relationship between the structure of the near wake, the surface loading on the edge, and the motion of the edge is characterized by flow visualization in conjunction with velocity and pressure measurements. The response of the near wake can be classified into two general categories: a modulated wake, characterized by ordered variations in the near-wake flow structure over a number of cycles of oscillation of the trailing edge; and a phase-locked wake, whereby the near-wake structure does not change from cycle to cycle of the edge oscillation. For the modulated wake, there are large, repetitive excursions of the near-wake vortex pattern in the stream wise direction due to coexistence of the self-excited global instability of the wake and the applied excitation. These excursions can have an amplitude two orders of magnitude larger than the amplitude of the edge motion. The duration of these excursions, in relation to the cyclic motion of the trailing edge, is deterministic. For the phase-locked wake, small changes of the edge oscillation frequency produce large changes in the phase shift of the initially formed vortex from the edge. These phase shifts are due to changes in the times required for vortex formation and departure from the near wake. The corresponding mechanisms are interpreted in terms of the crucial topological features of the near wake and a phase clock concept.

An Experimental Study on the Vertical Flow Past a Finite-Length Horizontal Cylinder at Low Reynolds Numbers

2014 ◽  
Vol 493 ◽  
pp. 68-73 ◽  
Author(s):  
Willy Stevanus ◽  
Yi Jiun Peter Lin
Keyword(s):  
Finite Length ◽  
Vortex Shedding ◽  
Vortex Formation ◽  
Reynolds Numbers ◽  
Horizontal Cylinder ◽  
Vortex Street ◽  
Vertical Flow ◽  
Low Reynolds Numbers ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

The research studies the characteristics of the vertical flow past a finite-length horizontal cylinder at low Reynolds numbers (ReD) from 250 to 1080. The experiments were performed in a vertical closed-loop water tunnel. Flow fields were observed by the particle tracer approach for flow visualization and measured by the Particle Image Velocimetry (P.I.V.) approach for velocity fields. The characteristics of vortex formation in the wake of the finite-length cylinder change at different regions from the tip to the base of it. Near the tip, a pair of vortices in the wake was observed and the size of the vortex increased as the observed section was away from the tip. Around a distance of 3 diameters of the cylinder from its tip, the vortex street in the wake was observed. The characteristics of vortex formation also change with increasing Reynolds numbers. At X/D = -3, a pair of vortices was observed in the wake for ReD = 250, but as the ReD increases the vortex street was observed at the same section. The vortex shedding frequency is analyzed by Fast Fourier Transform (FFT). Experimental results show that the downwash flow affects the vortex shedding frequency even to 5 diameters of the cylinder from its tip. The interaction between the downwash flow and the Von Kármán vortex street in the wake of the cylinder is presented in this paper.

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