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The effect of acoustic excitation on the aerodynamic performance of NACA0015 aerofoil at $\alpha=11^{\circ}$ and $Re_c = 1.0 \ x 10^6$ based on $c=0.35m$ chord length is investigated numerically using Improved Delayed Detached Eddy Simulations (IDDES). Flow separation is observed over the suction surface in the uncontrolled flow that forms a separated shear layer, resulting in aerodynamic performance degradation. External acoustic excitation is used in controlling the flow separation by exciting the separated shear layer. Acoustic excitation frequency and amplitude are the control parameters considered. The flow field is excited at a frequency of the most amplified disturbances and at first harmonic and sub-harmonic frequencies with a constant excitation amplitude. Unlike the harmonics, when the separated shear layer is excited at $F+=1$, the separation characteristics of the uncontrolled flow field are significantly altered. Unsteady disturbances are locked into the excitation frequency and transition is promoted within the shear layer. A separation bubble is generated over the suction surface with a reattachment region aft of the aerofoil surface. Vortex coherence and organized wake structures are also improved. The effect of excitation amplitude is investigated at the frequency of the most amplified disturbances. Increasing the excitation amplitude has two predominant impacts; it delays the boundary layer separation and advances the reattachment location, thereby reducing the separation bubble length. The results also suggest that there is a maximum effective acoustic excitation amplitude.

Fluidic valves based on the Coand\u{a} effect are increasingly being considered for use in aerodynamic flow control applications. A limiting factor is their variation in switching time, which often precludes their use. The purpose of this paper is to demonstrate the closed-loop control of a recently developed, novel piezo-fluidic valve that reduces response time uncertainty at the expense of operating bandwidth. Use is made of the fact that a fluidic jet responds to a piezo tone by deflecting away from its steady state position. A control signal used to vary this deflection is amplitude modulated onto the piezo tone. Using only a pressure measurement from one of the device output channels, an output-based LQG regulator was designed to follow a desired reference deflection, achieving control of a 90 m/s jet. Finally, the controller's performance in terms of disturbance rejection and response time predictability is demonstrated., Comment: 31 pages, 23 figures. Published in AIAA Journal, 4th May 2020

Future manned and unmanned aircraft are likely to exploit operation at high-angle of attack regions of the flight envelope where there are large unsteady aerodynamic effects. Understanding these effects is of paramount importance for design and certification of flight control systems that will operate correctly in and harness the benefits of such extreme areas of the flight envelope. A significant amount of research effort has gone into developing nonlinear mathematical models that would predict accurately aerodynamic forces and moments in unsteady regimes. The purpose of this paper is to demonstrate an alternative strategy for studying aircraft behaviour in unsteady regimes through the application of hardware-in-the-loop concept to dynamic wind tunnel testing. The paper presents preliminary experimental results for the free flight prediction of a pitching airfoil at high angles of attack and evaluates its accuracy.

Hardware-in-the-loop simulation is often used to evaluate the effectiveness of missile seeker sensors and guidance control systems in engagement scenarios. This paper describes a novel application of hardware-inthe-loop concept to wind-tunnel testing of aircraft. As unsteady aerodynamics are difficult to model numerically we propose a framework within which we can predict experimentally trajectory of aircraft in free flight. To demonstrate the concept, we consider an example for predictions of an airfoil trajectory in pitch in a falling free flight.

This paper presents some novel ideas on building a low cost hardware-in-the-loop simulator for free flight simulation of unmanned air vehicles. We postulate that to achieve maximum transparency of hardware-in-the-loop simulation it is necessary to match the boundary conditions around the aircraft such that in terms of interaction with the environment the aircraft does not feel a difference between being flown in the lab and being in free flight. We introduce a pefromance index based on some recent research and we present a possible hardware and software architecture for a 2-DOF free flight simulator that is currently under development.