Incompressible aerodynamiic performance of aerofoil blades of various configurations

Abstract

Plow over can~ered aerofoils with thickness to chord ratios of 10.82%,12.99%,16.24%, and 18.5690 were numerically modelled using k-w method for boundary layer flows. The aerofoils were of 5?o, 6% and 7% camber and were modelled at incidence angles between

_2° and 8°. Momentum thickness and momentum form parameter in the laminar flow region were evaluated by 'I'hwa i.t.se method, and skin friction was determined from the momentum integral equation. Transition is determined by Eppler's equation which is based on the ratio of energy thickness to momentum thickness. Flows in the transition and turbulent regions were evaluated by k-w method which deploys the equilibrium parameter in the outer region. This rnet.hod evaluates cHsplacement thickness and momentum thickness by numerical integration and then calculates skin friction from modified momentum integral equation. This program handles two iterations for the viscid-inviscid interactions for the values to converge. The k-w method is found to work very well even with flows which are just about to separate. Numerical results obtained showed expected distribution of displacement thickness, momentum thickness, momentum form parameter and skin friction. Displacement thickness, momentum t bickness and momentum f orrn pe rarnte r are all found to increase wit.h increase in angle of incidence and camber but decrease with increase in thickness to chord ratio. On the other hand skin friction was found to be a function of Reynolds number based on momentum thickness only. For the thinnest aerofoil, 10.82% thickness to chord ratio, no laminar separation was noticed, though separation can be possible w i t h high camber and high incidence'angle.

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Pressure distributions over the aerofoils were found to vary slightly with thickness to chord ratio. The drag coefficient was found to be negligibly affected by camber and incidence angle at low incidence but it decreased with increase in thickness to chord r~tio. Tapering the blades revealed that drag decreases with increase in taper to a minimum and then increases while both power and lift increase to a maximum and then decreases. On comparing the results of the k-w model with experimentally measured data for pressure coefficient and skin friction for aerof oi I Eppler E193, results for skin friction compare very well with experimental data while for the pressure coefficients

there was poor comparison between numerical model and experiments.