Wiper blades disturb the flow at the base of windshields, and the associated turbulence contributes to cabin noise through the window. This is more pronounced on airliners than automobiles even though their glass is much thicker, because of the high dynamic pressure, smoother underlying shape, and sweep angle. The response of the glass is highly dependent on many characteristics of the pressure fluctuations including spectrum, spatial patterns, and propagation velocities. This motivates numerical efforts aimed at the accurate and detailed prediction of these properties, and the exploration of methodological improvements, which would take the entire chain of events into account, from the wiper to the ears. The simulations are run at flight Reynolds numbers, which precludes simple Large-Eddy Simulation (LES) for cost reasons. Instead, the present study employs Reynolds-Averaged Navier-Stokes (RANS) modelling in the attached flow region upstream of the blade, combined with a recent version of DES called Improved Delayed Detached-Eddy Simulation or IDDES in the complex flow region. The wiper system is idealized. In particular, it includes only the wiper blade, i.e., it neglects the arm and the mechanisms attaching the blade to the arm and the arm to the wiper motor. In addition, the geometry of the blade itself does not account for subtleties of its shape nor for its finite span size, i.e., the blade is considered as an infinite rectangular obstacle, and both the upstream part of the airplane fuselage and the windshield are assumed to be flat and to have infinite extent. Periodic conditions are then applied in that direction, and the sensitivity to the period tested. The technical challenge is RANS-IDDES coupling, i.e., supplying an attached incoming boundary layer with LES content of good quality. The coupling procedure used here is based on triggering turbulent content at the RANS-LES interface by allowing the RANS and LES fields to overlap over some distance. In this case the two fields coexist on the same grid, so that natural turbulent content available in the LES field far enough from the inlet of the LES inflow section can be transferred upstream (recycled) to this section. The idea is similar to the recycling technique proposed by Lund et al (1998) for imposing inflow boundary conditions in pure LES and used later on in a simplified form by Spalart et al (2006), but is more general because a pressure gradient is present. Space limitations do not permit to present a detailed presentation of the developed procedure, and so we provide only an outline of its basic ideas.
Detached-eddy simulation over a simplified windshield wiper
2008
6 Seiten, 14 Bilder, 6 Quellen
Conference paper
English
Windshield wiper device, windshield wiper and method for operating windshield wiper device
European Patent Office | 2023
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