Numerical simulation of wake vortex detection using a radio acoustic sounding system

A parallel, two-dimensional Euler, one-dimensional Maxwell code is develope d to numerically simulate wake vortex detection using a radio acoustic soun ding system. The code is written in Fortran 90 with the message passing int erface for parallel implementation. The main difficulty with a time-accurat e simulation is the number of samples required to resolve the Doppler shift in the scattered electromagnetic signal. Even for a one-dimensional simula tion with typical scatterer size, the CPU time required to run the code is far beyond currently available computer resources. Two alternatives that ov ercome this problem are described. In the first, the code is run for a fict itious speed of light. Second, the governing differential equations are rec ast in order to remove the carrier frequency and solve only for the frequen cy shift using an implicit scheme with large time steps. The numerical stab ility characteristics of the resulting discretized equation with complex co efficients are shown. The code is run for both the approaches with Taylor a nd Oseen vortex velocity profiles. Finally, the Abel transform is applied t o the outputs of both explicit and implicit schemes, and the wake vortex ve locity field is retrieved with very good accuracy.