Numerical Analysis of Supersonic Inlet Buzz Characteristics under Various Throttling and Angle of Attack Conditions

Abstract

The present study numerically investigates the flow instability around supersonic inlet, called inlet buzz. Though the flow conditions change linearly, behavior of inlet buzz alters hysteretically. In order to simulate the inlet buzz hysteretic character, computations are conducted with varying mass flow rate and angle of attack. The mass flow rate condition is controlled by an exit throttling plug which moves back and forth to change an exit area. For angle of attack study, three dimensional inviscid simulations are conducted. Firstly, a set of simulation with mass flow control is presented. This simulation focuses on hysteretic buzz characteristics of supersonic inlet according to mass flow and the historic path of the mass flow change. Before the set of simulation, an inlet without a center-body is calculated to validate basic resonance mode results. In the next, an inlet buzz case with decreasing mass flow rate is simulated. In this process, the inlet buzz characteristic changes from the first mode of a low frequency regime to the second mode of a high frequency regime. Lastly, the effect of the increasing mass flow rate on the inlet buzz is examined. This case shows another kind of the buzz transition that the buzz frequency becomes higher in the third mode. The hysteretic inlet buzz has many similarities to the fundamentals of a pipe-type musical instrument such as self-excited feed-back mechanism and overblowing. Considering the similarities, the hysteretic characteristics of an inlet buzz is discussed in the instrumental acoustic point of view. In the second step, an investigation of angle of attack effects on inlet pressure oscillation is carried out with three-dimensional inviscid simulation intended to examine a tendency of inlet buzz briefly. It is seen that the major physical characteristic of the inlet pressure oscillation can be obtained by inviscid computations and the computed flow patterns inside and around the inlet are qualitatively consistent with the experimental observations. It is found that patterns of pressure oscillation histories and distortion due to asymmetric (or three-dimensional) shock structures are substantially affected by angle of attack. The dominant frequency of the existing inlet pressure oscillation does not change noticeably even in regards to a wide range of angle of attacks. However, the increasing angle of attack condition initiates a pressure oscillation from a steady state of inlet at low angle of attack.