Abstract: A two measurement at one point method with a two colour LDA(Laser Doppler Anemometer)has been used for measuring three dimensional velocity field.Various velocity distortions of the simulator have been investigated.The velocity and turbulence patterns of 90 degree torus quadrant and of torus with 20 degree slanted cut are shown.It can be seen clearly how the low velocity and large turbulence region will be caused by the flow separation from the duct lips.In order to estimate maximum instantaneous distortion,the vortex size must be measured.It is defined classically by velocity crelation and more directly than by total pressure.Some typical results are shown in a table.The vortex size is increased by the flow velocity.At 1D section the vortex size of torus with 20 degree slanted cut is about two times larger than the size of 90 degree torus quadrant.But at 3D section the former decreases and the later increases slightly.