Estimation of Time-Resolved Three-Dimensional Velocity Fields of Underexpanded Jets in Flapping Screech Mode

A method for estimating time-resolved three-dimensional velocity fields from non-time-resolved particle image velocimetry (PIV) and time-resolved near-field acoustic data is proposed and evaluated on a screeching, underexpanded jet. Multi-time-delay modified linear stochastic estimation (MTD-mLSE) is applied to the reduced-order PIV data and the Fourier coefficients of the azimuthal modes of sound pressure data of eight microphones arranged in a ring. The dominant screech tone at a nozzle pressure ratio of 2.97 corresponds to the first asymmetric mode. Time-resolved three-dimensional velocity fields corresponding to this mode are estimated, and flow structures associated with the flapping oscillation are observed. The obtained result shows that the velocity fluctuations are large near the screech source location of the B (flapping) screech mode.