Abonnement à la biblothèque: Guest
TSFP DL Home Archives Comité de direction

GENERALIZED PHASE AVERAGING OF EXPERIMENTAL SURFACE-MOUNTED BODY WAKE MEASUREMENTS: 3D COHERENT STRUCTURES & DYNAMICAL MODELS

J. A. Bourgeois
Deptartment of Mechanical and Manufacturing Engineering University of Calgary 2500 University Drive NW, Calgary, Alberta, T2N 1N4, Canada

Bernd R. Noack
Berlin Institute of Technology MB1 Strasse des 17. Juni 135, D-10623 Berlin, Germany; Departement Fluides, Thermique, Combustion Institut PPRIME, CNRS UPR 3346 CEAT, 43 rue de I'Aerodrome, F-86036 Poitiers, FRANCE

Robert J. Martinuzzi
Department of Mechanical and Manufacturing Engineering Schulich School of Engineering, University of Calgary 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4

Résumé

A six-dimensional model is proposed as a low-order representation of the vortex dynamics in the turbulent wake of a wall-mounted square-cross-section cylinder of height-to-width ratio h/d = 8 with one face normal to the flow at a nominal Reynolds number of 12,000. The wake flow is experimentally investigated for two oncoming turbulent boundary layers of thickness δ/d = 0.72 and 2.6 using simultaneous planar PIV and surface pressure measurements. A novel generalized phase averaging technique is used to determine global harmonic and shift modes, representing the shedding instability and low-frequency behaviour, respectively. The generalized phase average provides a parametrization of the phase as well as the oscillation amplitude and base flow drift. Using this technique, two distinct coherent structure topologies are found, depending on δ/d, distinguished by the topology of the stream/cross-streamwise vortical strands giving rise to half-ring and full-ring structures for the thinner and thicker boundary layer, respectively. A six-dimensional model is derived where the state of the system, f(a(t), ξ(t)), depends on the vector of mode amplitudes, a(t), and a stochastic term, ξ (t), simulating higher order contributions.