A Nonlinear Indicial Response model for forebody tangential blowing at high angles of attack

Abstract

This paper presents the development of a nonlinear aerodynamic model that describes the impact of forebody tangential blowing (FTB) on the generated roll moment for a fixed aircraft attitude. This model uses Nonlinear Indicial Responses (NlR) and incorporates physical insight gained from experimental data. The model accounts for the nonlinear aerodynamic behavior observed when FTB is applied at high angles of attack. Its predictions for the roll moment generated by FTB are compared to actual data and a model that uses a tirstorder lag of the static loads. The NlR model is found to provide a better prediction of the measured transient response. Experimental results used in the model’s development are discussed. They include flow visualization as well as static and dynamic measurements of the aerodynamic loads for various roll angles and blowing mass flow rates. The experimental apparatus used in this study is described and consists of an FTB-equipped wind tunnel model which is free to roll. The model is a wing-body combination with slots on the forebody for tangential blowing and is nominally set at 45 degrees angle of attack. To augment the control of a flight vehicle at high angles of attack, several methods of active flow control have been proposed and explored.4*5 They provide a means to alter the flow structure in a rational manner and increase the controllability of the vehicle under these flight conditions. The injection of thin sheets of air tangentially to the forebody of the vehicle has been found to be an extremely promising method6-8 and progress has been made in demonstrating the feasibility of using Forebody Tangential Blowing (FTB) to control the roll-yaw motion of flight vehicles through both experimental demonstrationsg*10 and simulations.” Experimental investigations into the use of FTB have been conducted at the low-speed wind tunnel of the Department of Aeronautics and Astronautics at Stanford University. The experimental apparatus consists of a wind tunnel model that is free to ro11.‘2 The model has a cone-cylinder fuselage and a sharp leading-edge delta wing. It is set at a nominal incidence angle of 45 degrees and is equipped with side slots to support the injection of a thin sheet of air tangentially to the forebody of the vehicle.