Abstract:
A simple "body+wing+flap+nacelle+propeller+horizontal tail" model(Model A) and two modified ones(Model B and C) were simulated via commercial CFD codes, using unstructured surface matching grid and multi-frame of reference technique to solve Reynolds Averaged Navier-Stokes(RANS) equations. For the simulations, the whole computational domain was divided into three individual domains, namely two rotating domains for the propellers and one stationary domain. The slipstream effects at low speed and in high thrust coefficient condition were studied. It has been demonstrated that the pitching static stability of'Model A'decreases sharply at low angles of attack, while increases slightly at high angles of attack due to the thrust generated by the propellers, the downwash effect of the wing and flap, and the interaction between the slipstream and horizontal tail(H-tail). Generally, the flow field around H-tail of a propeller-driven aircraft is affected by the general layout, the angle of attack, the downwash of the wing and flap, and the slipstream effect. More specifically, the downwash rate of the wing and flap increases due to the slipstream effect, while the efficiency of the H-tail decreases throughout the whole computed range of angles of attack. Since H-tail is not immersed in the slipstream, the high-energy fluid can hardly be utilized to increase its efficiency at low angles of attack. Moreover, it can be seen that the left H-tail contributes to the stability of'Model A'due to the counter-clockwise rotation of the two propellers.In order to improve the efficiency of H-tail, designers are suggested to modify the relative position between H-tail and the propeller slipstream to make sure that H-tail can be surrounded by high-energy flow generated by the propeller. Moving up the propeller by 0.7m(Model B) or moving down the H-tail by 0.86m(Model C) has been proved as feasible modifications to increase the pitching static margin at low angles of attack.