School of Aerospace Engineering, Xiamen University, Xiamen, Fujian Province, 361005, P. R. China
AECC Hunan Aviation Powerplant Research Institute, Zhuzhou, Hunan Province, 412000, P. R. China
An improved delayed detached eddy simulation (IDDES) is carried out to investigate both the mean and the instantaneous flow characteristics of conical cavities fixed on a cone surface in a Mach 0.9 freestream. Two model categories, a single cavity model with different length (L) to depth (D) ratio and a multi-cavity model that inserted the separation disk into a single cavity are studied. Results indicate that in case of a single cavity model, the cavity L/D ratio is the key parameter that influences mean flow structure and oscillatory characteristics. The bulk reverse flow structure can be broken up into smaller structures as L/D value reduces from 4.0 to 0.51 inside the cavity. Smaller longitudinal pressure gradients on the cavity wall and the thicker downstream boundary layer are observed when larger L/D values are present. The cavities with smaller L/D values can stimulate the pressure oscillation fundamental frequency as well as the acoustic tones to increase the value. Multi-cavity configurations through insertion of a separation disk into the single cavity are helpful in cutting the large reverse flow structure inside a cavity into a smaller, similar, coherent structure, and to reduce the overall cone drag. The insertion of the separation disk can modulate pressure oscillation peaks and sound pressure levels to higher frequency, however, they are not able to reduce the overall sound pressure inside the cavity. Pressure oscillations within each cavity of the multi-cavity configuration have a weak correlation.