Modeling and Control of Dynamic Stall Loads on a Smart Airfoil at Low Reynolds Number

Ayman Mohamed,David Wood,Jeffery Pieper

doi:10.3390/en14164958

Abstract

This article describes the development and testing of a modified, semi-empirical ONERA dynamic stall model for an airfoil with a trailing edge flap—a “smart airfoil”—pitching at reduced frequencies up to 0.1. The Reynolds number is 105. The model reconstructs the load fluctuations associated with the shedding of multiple dynamic stall vortices (DSVs) in a time-marching solution, which makes it suitable for real-time control of a trailing edge flap (TEF). No other model captures the effect of the DSVs on the aerodynamic loads on smart airfoils. The model was refined and tuned for force measurements on a smart NACA 643-618 airfoil model that was pitching with an inactive TEF and was validated against the measurements when the TEF was activated. A substantial laminar separation bubble can develop on this airfoil, which is challenging for modelers of the unsteady response. A closed-loop controller was designed offline in SIMULINK, and the output of the controller was applied to the TEF in a wind tunnel. The results indicated that the model has a comparable accuracy for predicting loads with the active TEF compared to inactive TEF loads. In the fully separated flow regime, the controller performed worse when dealing with the development of the laminar separation bubble and DSVs.

Highlights

Iwona Nowak and FrancescoThe interest in affordable wind energy production has led to technological innovations such as the smart rotor in which the time-dependent loads, induced by unsteady conditions, are controlled by active aerodynamic devices
The wind tunnel measurements at β = 0◦ were used to tune the coefficients of the modified ONERA dynamic stall model, whereas the measurements at β 6= 0◦ were used for validating the approach of utilizing the change in Cq,lin and ∆Cq to simulate the influence of actuating the trailing edge flap (TEF) on the unsteady loads
After modeling the unsteady loads on the smart airfoil, the dynamic stall model was utilized to tune the gains of a PID controller in SIMULINK/MATLAB, which is shown in Figures A4 and A5 in Appendix A

Summary

Introduction

The interest in affordable wind energy production has led to technological innovations such as the smart rotor in which the time-dependent loads, induced by unsteady conditions, are controlled by active aerodynamic devices. Instead of using the typical approach of pitching the airfoil and utilizing the TEF to alleviate the unsteady loads, Frederick et al [19] used a bluff body in front of a smart NACA 0012 airfoil model to generate a flow disturbance that simulates the unsteady loading of a wind turbine blade by atmospheric turbulence. In this experiment, the 0.04c long TEF was controlled using Proportional-Integral-Derivative (PID) and Linear.

Experimental Setup

Steady and Unsteady Measurements for the Clean NACA 643 -618 Airfoil

The Modified ONERA Dynamic Stall Model for Smart Airfoils

Modeling Unsteady Loads on Smart NACA 643 -618 Airfoil

Findings

Conclusions