Effect of Surface Unsteady Pressure Field on Global Beam Jitter for a Hemisphere-on-Cylinder Turret

Simultaneous point surface pressure measurements, accelerometer, optical wavefront and jitter measurements were performed using a hemisphere-on-cylinder turret with realistic geometric features like “smiles” at M = 0.33 and M = 0.4. A Linear Stochastic Estimation (LSE) technique was used to separate the aero-optical and the aero-mechanical jitter components. The unsteady pressure field on the turret was approximated using a combination of LSE technique and Proper Orthogonal Decomposition. To determine the driving factors of the aero-optical jitter, correlations were performed between the global POD modes, local pressure sensors and the measured aero-optical jitter. To further investigate sources of aero-optical jitter, correlations were performed between dominant wavefront modes and the measured jitter. It was found that different flow features, primarily the unsteady separation line, wake vertical global motion and the vortical structures formed in the separated wake influence the aero-optical jitter, both indirectly via Biot-Savart induction mechanism and directly, when crossing the laser beam. It was also found that different flow features affect the aero-optical jitter at different frequency ranges. Total jitter reduction based on the LSE technique is discussed and possible expansion of the technique using surface pressure measurements is investigated.