Aerodynamic Characteristics Of Rotor Research Articles

Comparative Study of Coaxial Main Rotor Aerodynamics in the Hover with the Usage of Two Methods of Computational Fluid Dynamics

The paper is focused on numerical modeling of the aerodynamic characteristics of a full-scale coaxial main rotor in hover. The simulation was performed using two approaches of computational fluid dynamics (CFD): the original free wake model (FWM) developed by the authors and the unsteady Reynolds-averaged Navier–Stokes (URANS) equations method based on the Ansys Fluent software. The structure of the rotor vortex wake, flow images, vorticity and induced velocity fields, total and distributed aerodynamic characteristics of the rotor, including the rotor performance and figure of merit diagrams, have been analyzed. A comparison between FWM/URANS based calculations and calculated/experimental data by other authors has been performed. A satisfactory match of these data confirms reliability of used methods when modeling the aerodynamic characteristics of coaxial rotors. The FMW demonstrates a significant advantage in speed and resources intensity when calculating the total aerodynamic characteristics of a coaxial rotor. The URANS method makes it possible to model with significant accuracy the effects associated with the blade vortex interactions and pressure distribution over the blade surface. Finally, conclusions about most effectiveness of joint application of considered methods in solving complex problems of coaxial rotor aerodynamics has been made.

Analysis of rotor aerodynamic response during ramp collective pitch increase by CFD method

In order to study the aerodynamic response characteristics of the helicopter rotor during ramp collective pitch increase, the moving-embedded grid technique is employed for numerical simulation. The governing equations are modeled via Navier-Stokes equations, as well as one equation S-A turbulence model. In order to improve the precision of unsteady simulation of the rotor flowfield, the three-order scheme known as Roe-WENO scheme is employed for the spatial discretization of convective fluxes, and the implicit LU-SGS scheme is adopted for the temporal discretization. The flowfield and aerodynamic characteristics of the SA349/2 Gazelle helicopter rotor are computed for verification, and thereafter, the present method is used to simulate the transient aerodynamic response of the rotor under different collective pitch increment rates. The unsteady flowfield and aerodynamic characteristics of the rotor under ramp collective pitch increase are obtained and compared with the experimental data. The results show that the numerical method not only can accurately predict the unsteady aerodynamic loads of the rotor in steady state, but also is capable of effectively simulating the transient aerodynamic response of the rotor, characterized by overshoot and delay phenomenon, during ramp collective pitch increase. Finally, the opposite ramp decrease in collective pitch and the influence of pre-twist on aerodynamic response are analyzed. The result shows that the transient aerodynamic response of the rotor under ramp collective pitch increase and decrease present a certain of symmetry. The change in pre-twist of blades only affects the thrust coefficient in steady state, while have little influence on the transient maneuvering process of collective pitch.

Experimental analyses of synthetic jet control effects on aerodynamic characteristics of helicopter rotor

ABSTRACTExperimental analyses of synthetic jet control (SJC) effects on aerodynamic characteristics of rotor in steady state and in hover were conducted. To ensure the structural strength of rotor and enough interior space for holding the synthetic jet actuators (SJAs), a particular blade with a frame-covering structure was designed and processed, and the experiment was conducted with low free stream velocities and rotor rotation speeds. There were three test conditions. In steady state, there were three free stream velocities (10m/s, 15m/s and 20m/s). In hover state, the rotor was worked with two rotation speeds of 180RPM and 240RPM. In forward flight, the rotor was worked with a rotation speed of 180RPM and a free stream velocity of 7.5m/s. To measure the synthetic jet control effect on rotor in stall, the range of collective pitch was set from 10° to 28° in steady state. The aerodynamic forces and sectional velocity field were measured by using the six-component balance and the Particle Image Velocimetry (PIV) system in the wind tunnel. Flow control effects on the blade based on the synthetic jets (SJ) were experimentally investigated with different jet parameters, such as jet locations, jet angles, and jet velocities. In steady state, the jet closer to the leading edge, and the jet angle of 90° had more advantages in improving the aerodynamic characteristics. Furthermore, the aerodynamic forces and sectional velocity field measurement of rotor in hover were conducted, it showed that SJAs could increase flow velocity at the upper surface, which led to lower upper surface pressure. As a result, the normal forces of rotor with two rotation speeds were increased significantly. These results indicated that the synthetic jet has a capability of increasing the normal force and delaying or preventing the stall of rotor.

V/STOLのホバリング/静止スラスト

As a practical parameter to represent the static and hovering thrust of V/STOL, the thrust to horsepower ratio T/_??_ is discussed instead of the usual figure of merit. T/_??_ is a function of tip speed besides the aerodynamic characteristics of rotor or propeller blade, and related to the horsepower per disc area ratio _??_c. T/_??_ can be very accurately formulated by means of a simple vortex theory, for instance, due to Prof. S. KAWADA. The transformation of usual torque versus thrust coefficient chart into _??_c versus T/_??_ chart is given, the latter being the phase plane of the former and convenient to illustrate rotor and propeller performance.