Publications from our researchers

The influence of the geometry of prismatic bodies on their aerodynamic sound emission is studied. Curle's formalism links the noise level to lift fluctuation and the spanwise organization of the flow coherent structures. Here, the acoustic field is measured using a set of microphones, and the flow spanwise coherence length is estimated from hot-wire velocity signals. An equivalent lift fluctuation is educed from the usual procedure of extrapolation of the sound level from 2D simulations to 3D long-span bodies. Circular and rectangular-of sectional aspect ratios (breadth-to-height ratio AR = b/d) of 1, 2 and 3-cross sections are tested for a Reynolds number range from 6,000 to 27,000. The closure of the problem and the influence of the geometry are addressed by confronting the educed lift coefficients to literature values at Reynolds numbers in the same range, and in the 2D laminar regime. Microphone measurements show that all over the tested flow velocities, the acoustic efficiency of the cross sections respects the following hierarchy: circular < AR = 2 < square < AR = 3. The coherence length at the vortex shedding frequency is around 5d for the circular and square sections, while it is around 20d for the two rectangular sections. Educed lift fluctuation values are found to be lower than those previously reported, and of the same order than those obtained in the 2D laminar regime. The flow spanwise coherence length at the vortex shedding frequency is found to be inversely proportional to the breadth based, RMS, educed lift coefficient.