Experimental and Numerical Investigation of the Near-Field Wake behind a Transport Aircraft with an Open Ramp

The near wake behind a transport airplane model with an open ramp is analyzed in multiple planes utilising stereoscopic and planar PIV as well as numerical RANS calculations. For cargo droppings information on the velocity fluctuations at the ramp is an essential safety requirement. The final PIV results enable a comparison with numerical data. Events in the near-wake observed with PIV and CFD are highlighted. Of particular interest is the evaluation of the capability of turbulence and grid modelling in complex separated flow structures. Five measurement planes were to be measured with PIV, 3 in a 3C-PIV and 2 in a 2C-PIV arrangement. Sample example result of the PIV data are given in figure 1. The set-up of the 3C-PIV and 2C-PIV meas-urement is chosen such that the cameras and laser light sheet for successive planes can be traversed. This en-ables fast calibrations during the measurement. A com-prehensive dataset of PIV results is obtained: for each PIV measurement point 500 image pairs are acquired. The numerical calculations are performed with a hybrid RANS TAU code employing an implicit Backward-Euler with LUSGS-Relaxation for the time discretization and a central method after Jameson for the space discretization. In order to adhere to the flow physics a low dissipative combina-tion of a scalar and matrix dissipation is used. The Spalart-Allmaras one-equation with Edwards-modification is used for the turbulence modelling. An increased resolution of free-stream vortices could be obtained with vortex corrections after FLOWer. A half model was used in the calculations and the grid was generated with Centaur. Especially in the aft region of the fuselage, around the opened ramp, special attention was devoted the grid generation. The total grid size compromised 13.8·10-6 grid points. Numerical calculations have been performed with and without model support