This paper describes the application of the Helicopter Multi-Block (HMB) CFD method to evaluate the performance of a series of tail rotor blades employing various tip designs. Selection of a good tip shape is important for tail rotors since they need to generate a substantial amount of thrust in near-hover yaw manoeuvres from blades with low radius/chord ratio. The tip shape must help to delay power divergence at the onset of stall at high incidence for tip Mach numbers in the region of 0.6, and have acceptable pitching moments in forward flight. All the rotor designs considered here start from the same simple configuration, and use a NACA0012 aerofoil, consistent with the datum model rotor blade for which existing data was available. A series of zero-twist tail rotor blades were designed with different tip shapes, including a squarecut tip, a volume-of-revolution tip, a swept-leading-edge, a parabolic tip, and several Kuchemann-type tips, some of which were equipped with anhedral. Following Euler evaluation in hover, three designs were compared in forward flight, and initial results have been obtained for selected blades using Navier-Stokes in hover. The computational method was first validated against available published experimental data for both main and tail rotors, and is here compared to tests on a model tail rotor in hover, for blades having 0, 8 and 16 degrees of twist, and subsequently used for the analysis of all the tail rotor blade designs put forward. Overall, the results of the computations indicate that, at low thrust, the Euler equations are adequate to represent the differences between the various tip shapes, at least as far as the induced power is concerned, while Navier-Stokes equations are needed to give a more complete assessment of tail rotor characteristics as the pitch setting and thrust becomes higher. The effects of twist and anhedral were well-represented, and in hover it was found that anhedral off-loads the tip, increasing the loading at mid-radius, in a broadly similar manner to twist. It is concluded that the current Helicopter Multi-Block (HMB) CFD method has the resolution to highlight differences in tip shape and is well suited for the preliminary design and analysis of helicopter blades.
Using CFD to understand and evaluate tail rotor blade designs
2008
21 Seiten, 11 Quellen
Aufsatz (Konferenz)
Englisch
Using CFD to Understand and Evaluate Tail Rotor Blade Designs
British Library Conference Proceedings | 2008
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