Airfoil Design for a Helicopter rotor blade Oct Han Gil Chae

Overview  Introduction Aerodynamic Characteristics of a Rotor Blade  Design Strategies Design Procedures Survey Optimization Methods  Analysis Tools Flow Solvers Optimization Code  Conclusions

Introduction  Aerodynamic Characteristics of a Rotor Blade

When Rotation Meets Translation...  An airfoil section meets different speed of air Periodically.  Angle of attack changes Periodically.  tw = -8 deg,  = 0.25 Angle of attack  Point design may not be optimum.

Design Strategies  Design Procedure Survey  Optimization Methods

Point Design : Airfoil from Cp Find an airfoil which meets given Cp distribution  May satisfy all the characteristics we want  Difficult to get the optimum Cp distribution

Point Design : Airfoil from Cl, Cd Find an airfoil which gives the best Cl/Cd characteristics  Easier than Cp  Possible worse performance at off-design points  May cause uneven surface Single pointMulti points

Robust Design : Design for uncertainties Probability of change in design point is considered  Better way for rotor blade airfoil  Still dealing with static characteristics Single point Robust

Dynamic Design : Near to the reality  The Best way for rotor blade airfoil  Requires an unsteady solver  Requires tremendous time Dynamic characteristics are considered

Optimization Methods  Restricted to design with Cp MGM Numerical RSM  Suitable for most applications  May cause unexpected results  Suitable for time consuming codes  Limited design range

Analysis Tools  Flow Solvers  Optimization Codes

Analysis Tools in Hand Panel XFOIL Pablo S2d Subsonic Steady Potential Panel N/S Potential Subsonic Inviscid Steady Inviscid Fortran Matlab Fortran CodeMethodRestrictionLanguage

Analysis Tools : Validation CLCDCM CL/CD  XFOIL gives reasonable solution in seconds NACA 0015, M=0.29, Re=1.59e6

Analysis Tools : Validation Cp Distribution  Most of codes generate good solutions NACA 0012, M=0.72, a=0 degNACA 0012, M=0.63, a=2 deg

Optimization : Procedure Calculate Derivatives Call XFOIL Find Steepest Direction Calculate Object function Call XFOIL Compare for Minimum Modify Airfoil Shape  Steepest Ascent Method

Optimization : Shape functions  Polynomial functions  Hicks-Henne functions

Optimization : Valication  Symmetric Airfoil (NACA ) Polynomial Hicks-Henne

Optimization : Valication  Cambered Airfoil (NACA 64110) Polynomial Hicks-Henne

Conclusions  What was done  Further study

What was done  Design method survey - Robust design method were selected  Analysis tool survey - XFOIL were selected  Optimization method - Steepest Ascent  Validation XFOIL gives reasonable results Hicks-Henne Shape function gives better results

Further Study  Basic sizing for reasonable M, Re and a  Random number generation for robust design  Modification of shape functions for T.E  Modification of optimization code

Questions ? Thank you