Characteristics of base pressure fluctuations of a typical missile configuration with a propulsive jet

Experiments were carried out to investigate the pressure fluctuations in the base region of a typical missile configuration at a freestream Mach number of 0.7 in the presence and absence of a propulsive jet. The objective was to characterize these pressure fluctuations and identify the underlying mechanisms responsible for their origin. Experiments included unsteady pressure measurements at six azimuthal locations and schlieren visualization. Substantial variation in the characteristics of pressure fluctuations is noticed along the azimuthal direction due to the asymmetry of the model. The probability density function (PDF) of pressure fluctuations indicates a significant drop in the peak PDF value and a substantial broadening at the highest nozzle pressure ratio (NPR). With an increase in NPR, the skewness decreases and approaches a Gaussian value while the kurtosis decreases and is seen to go below that of a Gaussian. Spectra of the pressure fluctuations indicate that the narrowband tones can be classified into three types based on the Strouhal number. Two types of tones among the three aforementioned are seen to be suppressed in the presence of the jet. Cross-correlation plots in the absence of the jet exhibit a large amplitude, low frequency oscillation which exists even after large separation times. On the other hand, in the presence of the jet, the oscillations dampen rapidly and vanish as the separation time increases. Finally, an attempt has been made to identify the possible primary mechanisms that are driving the base pressure fluctuations based on the observed characteristics of the acquired unsteady pressure signal.