The flow behind a backward facing step of 6 mm in height has been investigated by means of highresolution tomographic PIV. The shedding of vortices was stabilized by acoustic excitation, enab領(lǐng) phaselocked measurements of the flow field in a volume of 70x95x7 mm3. The gathered vector volumes with a vector spacing of approx. 0.25 mm in each direction were investigated by the method of conditional averaging. Basic flow structures, related to Q2 and Q4-events were extracted and their development in time was characterized, using methods of joint probability density functions of the fluctuations and of the invariants of the velocity gradient tensor. 自適應(yīng)粒子成像測(cè)速場(chǎng)儀（PIV） 德國(guó)LaVision PIV/PLIF粒子成像測(cè)速場(chǎng)儀 體視層析粒子成像測(cè)速系統(tǒng)(Tomo-PIV)