Investigation on the unsteady aerodynamics of cycloidal propeller in hovering flight

Abstract

The aerodynamics of a cycloidal propeller operating in hovering flight is systematically studied using numerical method. By solving the time-dependent incompressible Navier–Stokes equations and using a dynamic mesh technique, the complex unsteady flow field around the cycloidal propeller and the time-varying aerodynamic forces are investigated. The wake flow deflection can be observed in the flow field of the cycloidal propeller, which results in a deflection of the thrust. Strong downwash around cycloidal propeller and unsteady interference between blades are induced by the rotation and pitch motion of the blade. The instantaneous vertical, horizontal and resultant thrusts fluctuate cyclically with the azimuths in a pattern similar to sinusoid, and although the direction of instantaneous resultant thrust varies in a comparatively large region during rotating, the direction of averaged resultant thrust produced in each revolution is almost constant at different rotation speeds. This is beneficial to the flight stability and maneuverability of a cyclogyro. When one blade moves upward, the aerodynamic forces of the blade are much higher than that produced when moving downward. With the increase of the blade number, the unsteady interference between blades and the wakes of other blades tend to be stronger, producing great effects on aerodynamic forces of the blades as well as the aerodynamic performance of cycloidal propeller.

Aerodynamic Analysis of an Unmanned Cyclogiro Aircraft

“…The CFD models developed a The phase angle is the angle between the negative y-axis and the pivot arm at the position of maximum local blade pitch angle; it occurs prior to reaching the bottommost blade position. by [21,22,23,14,11,24,25,26,6] are all two-dimensional. [11] notes that the flow at midpsan and forces of a single rotor subjected to inflow is well represented by a 2D CFD model.…”

“…They report interaction between blades near the position of peak force. However, [24] mentions that the flow is highly three-dimensional They rely on the k-ω-SST turbulence model with a RANS CFD method. They also used a deforming mesh along with mesh refinement and 400 steps per rotation.…”

“…[6] report that a 3D model would reduce the uncertainty of the CFD modeling of cycloidal rotors. [24] also mentions that high magnitude pitching functions make a solution without CFD unfeasible. [27] developed both 2D and 3D CFD models and concludes that cycloidal rotor flow is highly three-dimensional and that the 2D code fails to grasp most of the flow unsteadiness.…”

Parametric Analysis of a Large-Scale Cycloidal Rotor in Hovering Conditions

“…Computational tools have been widely used for analysing the influence of several fluid-dynamic effects on the aerodynamic behaviour of pitching aerofoils (Wang et al 2012;Gharali and Johnson 2013), rotary wings (Laxman et al 2013) and on the efficiency of cyclogyros (Tang et al 2015). For instance, it was demonstrated, through the usage of numerical tools, that the unsteady interference among blades can significantly alter the flow uniformity on the downstream blades, affecting their aerodynamic performance (Iosilevskii and Levy 2003;Iosilevskii and Levy 2006).…”

Investigation of all-speed schemes for turbulent simulations with low-speed features

“…2 Among the turbulent flow computation methods, direct numerical simulation (DNS) and large eddy simulation (LES) remain impractical for most industrial flows, especially for high Reynolds flows involved with wall boundaries. 4 In fact, according to a survey by AIAA, 5 Reynoldsaveraged Navier-Stokes (RANS) turbulence models are believed to be still in wide use for between 20 and 50 years due to their successful predictions in attached flows and high efficiency. Moreover, hybrid RANS/LES methods combining the advantages of RANS and LES have progressed rapidly in recent 20 years.…”