Large scale structures of high Reynolds number turbulent boundary layers
Seminar Room 1, Newton Institute
Time-resolved measurements from the European Wallturb consortium experiment conducted using the large Laboratoire de Mecanique de Lille (LML) wind tunnel at Lille, France are reported. Data were taken at Re_theta = 9,800 and 19,100. Data were obtained using a rake of 143 single hot-wires which were spaced logarithmically across the flow in the spanwise and vertical directions over a distance approximately equal to the boundary layer thickness of 0.3 m. The wires were calibrated in situ using data from the simultaneous PIV experiment in a plane just upstream of the wire. Other PIV planes were also recorded in synch with the hot-wire data acquisition. This paper reports the cross-correlations and spectra generated among the wires themselves and those generated the upstream PIV plane immediately upstream of the rake. The existence of very long elongated structures are also shown by the space-time correlations obtained using the hot-wire rake data. Proper orthogonal decomposition (POD) applied on the same how-wire rake data are found to be very efficient in term of energy such that only a few spanwise wavenumber modes are necessary to capture 90% of the energy, and the details POD results like eigenspectra and eigenfunctions are discussed in the paper.