Supersonic flow unsteadiness induced by control surface deflections

TL;DR

This study investigates how different control surface deflections on a supersonic body induce flow unsteadiness, affecting pressure, acoustic loads, and flow structures, using high-fidelity simulations at Mach 2.0.

Contribution

It provides detailed computational analysis of flow unsteadiness caused by control surface deflections in supersonic flow, highlighting the relationship between deflection angles and flow instability.

Findings

Minimal pressure fluctuations at small deflections (~π/36 rad)

High acoustic loads (~150 dB) at large deflections (~π/2 rad)

High-frequency fluctuations and shear layer shedding at intermediate angles

Abstract

Control surface deployment in a supersonic flow has many applications, including flow control, mixing, and body-force regulation. The extent of control surface deflections introduces varying flow unsteadiness. The resulting fluid dynamics influence the downstream flow characteristics and fluid-structure interactions severely. In order to understand the gas dynamics, an axisymmetric cylindrical body with a sharp-tip cone at zero angles of attack ($\alpha=0^\circ$) is examined in a free stream Mach number of $M_\infty=2.0$ and Reynolds number of $Re_{D}=2.16 \times 10^6$ ($D=50$ mm). Four static control surface deflection angles ($\theta = \pi/36,\pi/6,\pi/3,\pi/2$, rad) are considered around the base body. The cases are computationally investigated through a commercial flow solver adopting a two-dimensional detached eddy simulation (DES) strategy. Recirculation bubble length, drag coefficient's variation, wall-static pressure statistics, acoustic loading on the model and the surroundings, $x-t$ trajectory and $x-f$ spectral analysis, pressure fluctuation's correlation coefficient on the model, and modal analysis are obtained to understand the flow unsteadiness. At $\theta = [\pi/36]$, the wall-static pressure fluctuations behind the control surface are minimal and periodic, with a mere acoustic load of about 50 dB. At $\theta = [\pi/2]$, a violent periodic fluctuation erupted everywhere around the control surface, leading to a higher acoustic load of about 150 dB (3 times higher than the previous). For $\theta = [\pi/6]$ and $[\pi/3]$, high-frequency fluctuations with small and large-scale structures continuously shed along the reattaching shear layer, thereby causing a broadened spectra in the control surface wake.