Development of an Improved Performance Function for the Control of Flow Separation

Abstract

Feedback control of aerodynamic flow separation is a formidable challenge due to the nonlinear system dynamics and the lack of a closed-form model that describes these dynamics. Recently, adaptive control approaches have been employed to meet this challenge. However, the performance and robustness achieved using these algorithms is limited due to the fact that the sensors in flow control systems are not used to estimate lift and drag, the quantities of interest. This paper derives a physics-based performance function that is based on estimating the ratio lift/drag and correlates closely with simulated and experimental aerodynamic performance. The developments are based on a NACA 0025 airfoil at a range of near-transitional Reynolds numbers and a range of pre-stall and post-stall angles of attack. The simulation and experimental results consider the use of four pressure measurements. Both the simulated and experimental results indicate that the resulting performance function has properties favorable to closed-loop control. The performance function developed here may be applied to any feedback control framework.

Nonlinear Adaptive Approach to Microjet-Based Flow Separation Control

“…18, 19, and 20 of Appendix A. These and more detailed data are presented in Reese et al 39 For the angles of attack and Reynolds numbers considered, Z lif t does increase and decrease in agreement with actual lift in both simulated and experimental data. .…”

“…The input for these tests was the solenoid valve voltage frequency, and the output was Z lif t , the lift based performance function computed from the transducer measurements at locations P1 through P4. This performance function, with a detailed derivation provided in Reese et al 39 with sensors located as indicated in Table 1, Z lif t may be computed as…”

“…Additional cases may be found in Reese et al 2014. 39 For simulated cases, the plots contain a comparison (for many angle of attack configurations) of Z lif t , computed using 4 pressure values taken from locations given in Table 1, with C L and C L /C D computed by evaluating integrals over 160 data points over the upper and lower airfoil surfaces. The experimental case given provides a comparison between Z lif t as measured from the four pressure transducers and lift values measured with a force balance.…”