Numerical Investigations of Transonic Cavity Flow Control Using Steady and Pulsed Fluidic Injection

A numerical study is conducted to investigate steady and pulsed fluidic actuation in transonic flow over an open cavity. Numerical results are obtained for the unsteady threedimensional flow with three different steady mass injection rates and one pulsed injection upstream of the cavity. The simulations are carried out using the full 3-D Navier Stokes equations with the two-equation k-ε based Detached Eddy Simulation (DES) model to calculate the flow and acoustic fields. Computational results are presented for unsteady pressure fluctuations, vorticity contours and kinetic energy profiles at different injection ratios. The sound pressure level (SPL) and the kinetic energy spectra highlight the effectiveness of actuation in tone attenuation at peak frequencies. The computed sound pressure level (SPL) spectra with and without injection are compared with available experimental data and LES predictions. INTRODUCTION Several investigations have been carried out to understand the complex flow physics associated with acoustic suppression in cavities. Passive suppression techniques like fences [1] and spoilers [2,3] had achieved limited success under certain operating conditions. An experimental study by Stanek et al. [4] investigated rods, spoilers and rods modified with circular end-caps, and linked high frequency rod shedding to acoustic suppression. Active control techniques have been considered efficient noise reduction tools effective over a wide range of operating conditions. These techniques include oscillating flaps [5], upstream steady mass injection [6], harmonic blowing [7,8], piezoelectric actuators [9,10] and powered resonance tubes [11]. Shaw and Northcraft [8] investigated the effect of steady mass injection upstream of the cavity, and suggested that at subsonic Mach numbers, SPL decreases with increased mass injection. Stanek et al. [12] conducted a thorough experimental study in subsonic and supersonic cavity flow fields using four high-frequency actuators (piezo-ceramic wedge, rod in cross-flow, passive resonance tube, and powered resonance tube) and a low frequency actuator (saw-toothed spoiler). They reported that the high frequency powered resonance tube was most effective in reducing the tones at peak frequencies. In a subsequent study Stanek et al. [13] compared the effect of steady and pulsed mass actuation and observed that a substantial amount of suppression can be attributed to the steady injection. They introduced the notion of superposition of steady effect and high frequency effect and proposed that high frequency forcing has stabilized the flow rather than draining energy out of the large scales as suggested by Glezer et al. [14]. Ukeiley et al. [15] investigated a powered whistle in supersonic flow and steady mass blowing of nitrogen helium and hot air in subsonic flow and observed that helium injection is most effective in decimating the Rossiter tones. Zhuang et al. [16] conducted experiments in supersonic cavity flow control using supersonic microjets at the leading edge, and reported a 10dB reduction in the overall SPL and 20 dB reductions at tonal frequencies. Fewer numerical studies have been conducted for cavity flow control. Cain et al. [17,18] performed 2D URANS simulations of harmonic mass injection in subsonic cavity flows and concluded that the mean mass flow plays a more important role than the actuation frequency for noise suppression. Rizzetta et al. [19] performed large eddy simulations (LES) of high frequency mass pulsing in supersonic cavity flows and studied the resulting suppression. Arunajatesan et al. [20,21] performed 2D RANS and 3D hybrid RANS/LES simulations of subsonic flow over cavity using a thin rod as suppression device. They showed that the 2D simulations exhibit a wake mode behavior, which is not consistent with experimental observation. The study presented auto and cross-correlation functions, two-point correlation tensors and turbulent and kinetic energy budgets from the 3D simulations in an attempt to explain the control mechanism. A number of computational studies performed by the current authors have reported computational results for cavity flow without actuation based on DNS [22], DES [23,24]. The DNS results [22] indicated a noticeable increase in pressure fluctuation amplitude with Mach number while the DES simulations [23,24] indicated that the sound pressure level increases with the flow Reynolds number. Preliminary studies on steady blowing by the current authors indicated a 7.5–10%