Loading...
Please wait, while we are loading the content...
Similar Documents
Phase averaged turbulence properties in the near wake of a circular cylinder at high Reynolds number using POD
| Content Provider | Semantic Scholar |
|---|---|
| Author | Perrin, R. Preston Braza, Marianna Cid, Emmanuel Cazin, Sébastien Barthet, Arnaud Sevrain, Allain Mockett, Charles Thiele, Frank |
| Copyright Year | 2006 |
| Abstract | The flow past a circular cylinder at high Reynolds number is studied by means of PIV, 3C-PIV and Time Resolved PIV techniques. One of the goals of this study was to allow comparisons with numerical simulations on a domain identical to that of the experiment. For this reason, the cylinder was placed in a confined environment, with a high blockage coefficient and a low aspect ratio, thereby allowing computations on a mesh of reasonable size, and avoiding ‘infinite conditions’. This paper deals with the decomposition of the flow into coherent and random parts, as well as briefly presenting a comparison with Detached-Eddy Simulations (DES) of the flow. To this aim, phase averaged quantities were first obtained using the wall pressure signal on the cylinder as a trigger signal. This was achieved using both conditional sampling and LSE with similar results. This decomposition is then analysed using the Time Resolved PIV (TRPIV) measurements, as well as by comparison of the contributions of the organised and turbulent fluctuations to the time-independent Reynolds stress tensor with those obtained from velocity spectra. In agreement with other studies, it is found that the contribution of the turbulent motions is overestimated as a result of the occurrence of phase lag between the trigger and velocity signals. A POD analysis then was performed to extract the coherent motion and to compare this decomposition with that obtained by phase averaging. Similarly to the phase averaging, the POD allows the decomposition of the time-independent stress tensor as the sum of two contributions corresponding to the first N modes, and the rest of the modes. This decomposition is then analysed by comparing these contributions to those obtained from the velocity spectra, according to the value of N chosen. It is found that these contributions are strongly dependent on N, and the contribution of the first modes greatly overestimate the coherent motion if N is too large. In order to obtain a good decomposition of the flow in coherent and random parts, the difficulty in this case lies in the choice of the number of modes. Finally, the POD coefficients of the first two modes are used instead of the pressure signal to determine the phase of the vortex shedding, and the phase averaging is reconsidered. It is found that the phase averaged vortices are less smeared by the averaging process, the turbulent stresses better follow the evolution of the vortices, and the contributions of both coherent and turbulent fluctuations are found to agree well with those evaluated from the velocity spectra. This enhancement is obtained because the phase angle is determined directly from the velocity fields to be averaged, thereby reducing the phase-lag effect. The comparison with DES demonstrates the high level of agreement obtainable between simulation and experiment, as well as giving an example of the kind of concrete evaluation which can be made. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://ltces.dem.ist.utl.pt/lxlaser/lxlaser2006/downloads/papers/09_1.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
