Energy Separation and Acoustic Interaction in Flow Across a Circular Cylinder

2001 ◽  
Vol 123 (4) ◽  
pp. 682-687 ◽  
Author(s):  
R. J. Goldstein ◽  
Boyong He
Keyword(s):  
Wind Tunnel ◽  
Circular Cylinder ◽  
Stagnation Point ◽  
Energy Separation ◽  
Acoustic Measurements ◽  
Velocity Measurements ◽  
Acoustic Interaction ◽  
Strong Energy ◽  
Separation Mechanisms ◽  
Rear Stagnation Point

Energy separation in a flow around an adiabatic circular cylinder is investigated using a surface-mounted thermocouple. Energy separation mechanisms in different regions around the cylinder are discussed. Velocity measurements near the rear stagnation point and acoustic measurements indicate that shedding vortices and the wind tunnel intrinsic resonant acoustics can strengthen each other when their frequencies match producing strong energy separation.

Oscillatory flow past a circular cylinder in a rotating frame

1997 ◽  
Vol 345 ◽  
pp. 101-131
Author(s):  
M. D. KUNKA ◽  
M. R. FOSTER
Keyword(s):  
Circular Cylinder ◽  
Steady Flow ◽  
Stagnation Point ◽  
Oscillatory Flow ◽  
Numerical Solutions ◽  
Initial Conditions ◽  
Temporal Integration ◽  
Oncoming Flow ◽  
Flow Past ◽  
Rear Stagnation Point

Because of the importance of oscillatory components in the oncoming flow at certain oceanic topographic features, we investigate the oscillatory flow past a circular cylinder in an homogeneous rotating fluid. When the oncoming flow is non-reversing, and for relatively low-frequency oscillations, the modifications to the equivalent steady flow arise principally in the ‘quarter layer’ on the surface of the cylinder. An incipient-separation criterion is found as a limitation on the magnitude of the Rossby number, as in the steady-flow case. We present exact solutions for a number of asymptotic cases, at both large frequency and small nonlinearity. We also report numerical solutions of the nonlinear quarter-layer equation for a range of parameters, obtained by a temporal integration. Near the rear stagnation point of the cylinder, we find a generalized velocity ‘plateau’ similar to that of the steady-flow problem, in which all harmonics of the free-stream oscillation may be present. Further, we determine that, for certain initial conditions, the boundary-layer flow develops a finite-time singularity in the neighbourhood of the rear stagnation point.

Effect of Aspect Ratio on the Flow Field Above the Free End of a Finite Circular Cylinder

2014 ◽  
Author(s):  
Noorallah Rostamy ◽  
David Sumner ◽  
Donald J. Bergstrom ◽  
James D. Bugg
Keyword(s):  
Wind Tunnel ◽  
Circular Cylinder ◽  
Recirculation Zone ◽  
Ground Plane ◽  
Symmetry Plane ◽  
Leading Edge ◽  
Velocity Measurements ◽  
Reattachment Point ◽  
Aspect Ratios ◽  
The Mean

The flow above the free end of a surface-mounted finite-height circular cylinder was studied in a low-speed wind tunnel using particle image velocimetry (PIV). The cylinder was mounted vertically in the wind tunnel, normal to a ground plane. The approaching flow was in the x-direction and the cylinder axis was aligned in the z-direction. Velocity measurements were made above the free-end surface in several vertical (x-z) planes and several horizontal (x-y) planes, for finite circular cylinders of aspect ratios AR = 9, 7, 5 and 3, at a Reynolds number of Re = 4.2×104. The relative thickness of the boundary layer on the ground plane was δ/D = 1.7. In the vertical symmetry plane, the mean velocity measurements show the prominent separation from the circumferential leading edge, the mean recirculation zone above the free-end surface, the arch vortex inside the recirculation zone, and reattachment of the flow onto the free-end surface. Experimental evidence is found for a leading-edge separation bubble, a flow structure which has been reported in some numerical simulations in the literature. As AR decreases, the reattachment point and the centre of the arch vortex move downstream, the recirculation zone becomes thicker, and the centre of the arch vortex moves higher above the free end. Away from the symmetry plane, the recirculation zone becomes thinner, the arch vortex centre moves upstream and closer to the free-end surface, and the reattachment point moves upstream. In the horizontal planes, measurements made very close to the surface can approximate the mean surface streamline topology, revealing the pair of foci representing the termination points of the arch vortex, the prominent curved reattachment line, reverse flow beneath the mean recirculation zone, and the reattachment and separation saddle points on the free-end centerline.

Crossflow Over a Porous Circular Cylinder With Surface Blowing: CFD Analysis With Experimental Validation

2012 ◽  
Author(s):  
T. H. Reif ◽  
F. A. Kulacki
Keyword(s):  
Circular Cylinder ◽  
Flow Field ◽  
Stagnation Point ◽  
Test Section ◽  
Free Stream ◽  
Absolute Error ◽  
Secondary Flows ◽  
Test Case ◽  
Positional Error ◽  
Rear Stagnation Point

Crossflow over a porous circular cylinder, with uniform blowing at the surface, was investigated experimentally and numerically. Two free stream conditions, Reynolds numbers 4,100 and 6,200, and five dimensionless blowing rate parameters (ratio of surface blowing to free stream velocity), 0.000 to 0.190, were studied experimentally. For simplicity, results for only one Reynolds number and three blowing cases are presented. A low speed wind tunnel was designed and constructed to give time-smoothed average velocities in the range of 61–122 cm/s. The tunnel was calibrated prior to the study. Velocity and pressure profiles were uniform up to 3.81 cm from the walls of the test section. Turbulence intensity, measured at the center of the test section, was 3.0% with an absolute error of 0.5%. Using hot wire anemometry, time-smoothed velocity profiles were measured at several radial and angular positions from the front to the rear stagnation point. The maximum absolute error in the velocity measurements was 12 cm/s and the positional error of the probe was 0.00254 cm. The numerical study employed the finite element method. The flow field was modeled as two-dimensional with half-symmetry. The unsteady, turbulent (k/ε) model had 2,160 elements and 2,287 nodes. Convergence and laminar flow was verified. When blowing was present, the numerical solution was found to give excellent agreement with the experiments in the entire flow field. For the no blowing test case, the agreement with the experiments was also excellent up to 20 deg from the rear stagnation point. Flow visualization, using smoke, was used to qualitatively study the large scale secondary flows in the wake region. These results helped explain the poorer agreement for the no blowing test case.

Suppression of Unsteady Vortex Shedding From a Circular Cylinder by Using a Passive Jet Flow Control Method

2014 ◽  
Author(s):  
Wenli Chen ◽  
Hui Li ◽  
Hui Hu
Keyword(s):  
Circular Cylinder ◽  
Flow Control ◽  
Stagnation Point ◽  
Vortex Shedding ◽  
Control Method ◽  
Aerodynamic Force ◽  
Jet Flow ◽  
Wake Flow ◽  
Cylinder Model ◽  
Rear Stagnation Point

A passive jet flow control method was employed to suppress the unsteady vortex shedding from a circular cylinder at the Reynolds number level of Re = (0.18∼1.1)×105. The passive jet flow control was achieved by blowing jets from the holes near the rear stagnation point of the cylinder, which are connected to the in-take holes located near the front stagnation point through channels embedded inside the cylinder. Since a part of the oncoming flow would inhale into the in-take holes, flow through the embedded channels, and blow out from the holes near the rear stagnation point to suppress/manipulate the alternating vortex shedding in the wake flow behind the circular cylinder, the present passive jet flow control method does not require any additional energy inputs for the flow control. In the present study, the aerodynamic force (i.e., both lift and drag) acting the circular cylinder model with and without the passive jet flow control were compared quantitatively at different Reynolds numbers (i.e., different inlet mean speed). It was found that, in addition to almost eliminating the fluctuations of the lift forces acting on the cylinder, the passive jet flow control method was also found to reduce the mean drag acting on the cylinder model greatly. The instantaneous vorticity distributions and corresponding streamline patterns were used to reveal the underlying physics about why and how the passive jet flow control method can be used to suppress the alternating vortex shedding and induce a symmetrical wake pattern behind the cylinder model.

scholarly journals Drag and pressure fields for the MHD flow around a circular cylinder at intermediate Reynolds numbers

2005 ◽  
Vol 2005 (3) ◽  
pp. 183-203 ◽  
Author(s):  
T. V. S. Sekhar ◽  
R. Sivakumar ◽  
T. V. R. Ravi Kumar
Keyword(s):  
Circular Cylinder ◽  
Drag Coefficient ◽  
Stagnation Point ◽  
Stokes Equations ◽  
Separation Bubble ◽  
Flow Direction ◽  
Boundary Layer Separation ◽  
Pressure Fields ◽  
Correction Technique ◽  
Rear Stagnation Point

Steady incompressible flow around a circular cylinder in an external magnetic field that is aligned with fluid flow direction is studied forRe(Reynolds number) up to 40 and the interaction parameter in the range0≤N≤15(or0≤M≤30), whereMis the Hartmann number related toNby the relationM=2NRe, using finite difference method. The pressure-Poisson equation is solved to find pressure fields in the flow region. The multigrid method with defect correction technique is used to achieve the second-order accurate solution of complete nonlinear Navier-Stokes equations. It is found that the boundary layer separation at rear stagnation point forRe=10is suppressed completely whenN<1and it started growing again whenN≥9. ForRe=20and 40, the suppression is not complete and in addition to that the rear separation bubble started increasing whenN≥3. The drag coefficient decreases for low values ofN(<0.1)and then increases with increase ofN. The pressure drag coefficient, total drag coefficient, and pressure at rear stagnation point vary withN. It is also found that the upstream and downstream pressures on the surface of the cylinder increase for low values ofN(<0.1)and rear pressure inversion occurs with further increase ofN. These results are in agreement with experimental findings.

Circular cylinder vortex-synchronization control with a synthetic jet positioned at the rear stagnation point

2010 ◽  
Vol 662 ◽  
pp. 232-259 ◽  
Author(s):  
LI HAO FENG ◽  
JIN JUN WANG
Keyword(s):  
Circular Cylinder ◽  
Stagnation Point ◽  
Large Scale ◽  
Water Channel ◽  
Excitation Frequency ◽  
Synthetic Jet ◽  
Reynolds Stresses ◽  
Flow Topology ◽  
Wake Vortices ◽  
Rear Stagnation Point

The flow over a circular cylinder controlled by a two-dimensional synthetic jet positioned at the mean rear stagnation point has been experimentally investigated in a water channel at the cylinder Reynolds number Re = 950. This is an innovative arrangement and the particle-image-velocimetry measurement indicates that it can lead to a novel and interesting phenomenon. The synthetic-jet vortex pairs induced near the exit convect downstream and interact with the vorticity shear layers behind both sides of the cylinder, resulting in the formation of new induced wake vortices. The present vortex synchronization occurs when the excitation frequency of the synthetic jet is between 1.67 and 5.00 times the natural shedding frequency at the dimensionless stroke length 99.5. However, it is suggested that the strength of the synthetic-jet vortex pair plays a more essential role in the occurrence of vortex synchronization than the excitation frequency. In addition, the wake-vortex shedding is converted into a symmetric mode from its original antisymmetric mode. The symmetric shedding mode weakens the interaction between the upper and lower wake vortices, resulting in a decrease in the turbulent kinetic energy produced by them. It also has a significant influence on the global flow field, including the velocity fluctuations, Reynolds stresses and flow topology. However, their distributions are still dominated by the large-scale coherent structures.

Acoustic Measurements of a Contra-Rotating Open Rotor in an Open Jet Wind-Tunnel

2012 ◽  
Vol 11 (2) ◽  
pp. 197-212 ◽  
Author(s):  
Stefan Funke ◽  
Larisa Kim ◽  
Henri Siller
Keyword(s):  
Wind Tunnel ◽  
Acoustic Measurements ◽  
Open Rotor
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