Numerical Study on Low-Reynolds Compressible Flows around Mars Helicopter Rotor Blade Airfoil

High-speed rotor rotation under the low-density condition creates a special low-Reynolds compressible flow around the rotor blade airfoil where the compressibility effect on the laminar separated shear layer occurs. However, the compressibility effect and shock wave generation associated with the increase in the Mach number (M) and the trend change due to their interference have not been clarified. The purpose is to clear the compressibility effect and its impact of shock wave generation on the flow field and aerodynamics. Therefore, we perform a two-dimensional unsteady calculation by Computational fluid dynamics (CFD) analysis using the CLF5605 airfoil used in the Mars helicopter Ingenuity, which succeeded in its first flight on Mars. The calculation conditions are set to the Reynolds number (Re) at 75% rotor span in hovering (Re = 15,400), and the Mach number was varied from incompressible (M = 0.2) to transonic (M = 1.2). The compressible fluid dynamics solver FaSTAR developed by the Japan aerospace exploration agency (JAXA) is used, and calculations are performed under multiple conditions in which the Mach number and angle of attack (α) are swept. The results show that a flow field is similar to that in the Earth’s atmosphere above M = 1.0, such as bow shock at the leading edge, whereas multiple λ-type shock waves are observed over the separated shear layer above α = 3° at M = 0.80. However, no significant difference is found in the Cp distribution around the airfoil between M = 0.6 and M = 0.8. From the results, it is found that multiple λ-type shock waves have no significant effect on the airfoil surface pressure distribution, the separated shear layer effect is dominant in the surface pressure change and aerodynamic characteristics.

Numerical Investigation on a Dual-jet Consisting of a Plane Wall Jet and a Parallel Offset Jet at Low-Reynolds Number

A dual-jet consisting of a wall jet and an offset jet has been numerically simulated using lattice Boltzmann method to examine the effects of jet spacing between two jet centerlines,defined as s.The Reynolds number based on jet-exit-width dis set to be Re = 56 and the jet spacing is set to be less than or equal 10 times the jet-exitwidth.Computational results reveal that the flow field displays periodic vortex shedding when the jet spacing is in the range of 9≤s/d ≤ 10,while it remains steady with two counter-rotating vortices in the converging region when s/d ≤ 8.When s/d = 9,the power spectral analyses indicate that the vortex shedding phenomenon has specific frequency.The significant oscillation stresses induced by the periodic components of velocities are found to mainly exist in the inner shear layer regions,implying stronger momentum transfer occuring in these regions.