Spanwise differences in static and dynamic stall on a pitching rotor blade tip model

An experimental investigation of static and dynamic stall on a rotor blade tip model with a parabolic tip geometry and aspect ratio 6.2 at a chord Reynolds number of 900,000 and a Mach number of 0.16 is presented. The resulting flow is analyzed based on unsteady surface pressure measurements and quantitative flow visualizations by high-speed particle image velocimetry. The flow separation is found to be delayed near the parabolic blade tip for static angles of attack as well as for sinusoidal angle of attack motions. The maximum effective angle of attack prior to stall is shifted to approximately two-thirds of the span outboard from the root because of a positive twist of the model with an increasing geometric angle of attack towards the tip. The stall onset is observed near the section with the maximum effective angle of attack, with a subsequent spanwise spreading of the flow separation. Different stages of flow separation for static angles of attack are identified one of them with the occurrence of two stall cells. During dynamic stall, the leading edge vortex formation starts near the maximum effective angle of attack and the pitching moment peak resulting from the passage of the dynamic stall vortex is higher at this section. Further inboard the maximum aerodynamic loads are of comparable magnitude whereas the outboard section shows reduced peaks due to the influence of the wing tip vortex.

[1]  W. J. Mccroskey,et al.  Dynamic Stall on Advanced Airfoil Sections , 1981 .

[2]  Markus Raffel,et al.  Particle Image Velocimetry: A Practical Guide , 2002 .

[3]  Peter F. Lorber,et al.  An Oscillating Three-Dimensional Wing Experiment: Compressibility, Sweep, Rate, Waveform, and Geometry Effects on Unsteady Separation and Dynamic Stall , 1992 .

[4]  Markus Raffel,et al.  The Dynamics of Static Stall , 2012 .

[5]  R. Galbraith,et al.  An Examination of Dynamic Stall on an Oscillating Rectangular Wing , 2003 .

[6]  A. Gardner,et al.  Boundary layer transition determination for periodic and static flows using phase-averaged pressure data , 2015 .

[7]  A. Gardner.  User guide for cp2cl plusm v3.x: A program to provide forces and moments from airfoil pressure , 2014 .

[8]  Markus Raffel,et al.  Dynamic stall development , 2013 .

[9]  F. B. Gustafson,et al.  Stalling of Helicopter Blades , 1946 .

[10]  C. Chatfield.  Continuous Univariate Distributions, Vol. 1 , 1995 .

[11]  N. L. Johnson,et al.  Continuous Univariate Distributions.Vol. 1@@@Continuous Univariate Distributions.Vol. 2 , 1995 .

[12]  Michel Costes,et al.  Numerical Investigation of Three-Dimensional Static and Dynamic Stall on a Finite Wing , 2015 .

[13]  J. Anderson,et al.  Numerical lifting line theory applied to drooped leading-edge wings below and above stall , 1980 .

[14]  Ken Badcock,et al.  Investigation of Three-Dimensional Dynamic Stall Using Computational Fluid Dynamics , 2005 .

[15]  Mark Potsdam,et al.  Rotor Structural Loads Analysis Using Coupled Computational Fluid Dynamics/Computational Structural Dynamics , 2014 .

[16]  Peter Lorber,et al.  Tip vortex, stall vortex, and separation observations on pitching three-dimensional wings , 1993 .

[17]  F. Scarano.  Iterative image deformation methods in PIV , 2002 .

[18]  J. Barlow,et al.  Flowfield Model for a Rectangular Planform Wing beyond Stall , 1980 .

[19]  R. A. Piziali,et al.  2-D and 3-D oscillating wing aerodynamics for a range of angles of attack including stall , 1994 .

[20]  Markus Raffel,et al.  Experimental Investigation of Dynamic Stall on a Pitching Rotor Blade Tip , 2016 .

[21]  L. Carr.  Progress in analysis and prediction of dynamic stall , 1988 .

[22]  S. Schreck,et al.  Unsteady vortex dynamics and surface pressure topologies on a finite pitching wing , 1994 .

[23]  William G. Bousman,et al.  A Qualitative Examination of Dynamic Stall from Flight Test Data , 1997 .

[24]  Westland Helicopters Ltd,et al.  Identification of Retreating Blade Stall Mechanisms Using Flight Test Pressure Measurements , 1989 .