Research On Unsteady Aerodynamic Models At High Angle Of Attack

This subject mainly researched on unsteady aerodynamic characteristics in large amplitude andaerodynamic modeling at high angle of attack.The unsteady test of the fighter model at different surportangles of attack and different forms of movement was carried out in NH-2low speed wind tunnel. Themovement included rolling motion, yawing motion and yawing-rolling coupled-motion.Firstly, in this thesis, comparing the difference and contract at different coupling ratio movement,the unsteady aerodynamic forces abtained by the test was investegated and anlysised, as well as whichcaused by the rate of sideslip. The result shows that, the unsteady aerodynamic forces are greatlydifferent at different coupling ratio movement but has very good continuity, and the unsteadyaerodynamic forces caused by the rate of sideslip has good linear relationship.Secondly, this paper investegated the modeling based on fuzzy logic principle and the calculationmethod of dynamic derivative. Increasing the modeling number of coupling ratio can improve theprecision of fuzzy logic modeling. The simulation method of dynamic derivative based on fuzzy logicmodeling can be used as a new caculation method of dynamic derivative.Thirdly, the unsteady aerodynamic force modeling methods by differential equations wasdiscussed in this paper. The hysteresis time of aerodynamic force has shown great relationship with thefrequency by the investegation of the differential equation model with two different forms. Then, amethod of ‘extrapolating’ unsteady aerodynamic forces was used, which had shown good agreementwith the result of simulation and test.Finally, the extrapolating model of unsteady aerodynamic force was investegated. This method isbased on unsteady aerodynamic model established by the rotary balance test and yawing-rollingcoupling motion test at large angle of attack.. The results show that the model fits the unsteadyaerodynamic force at high frequency movement very well, thus the restriction that high frequencymotion test can’t be carried out due to laboratory equipment inertia can be solved.