ADVANCED LOW REYNOLDS NUMBER TESTING FACILITY

摘要

The advent of micro aerial vehicles (MAV) and advanced flow control methods (MEMS) has significantly increased the need for a better understanding of very low Reynolds number flows. Aerodynamic testing in this flow regime using conventional facilities, such as wind or water tunnels, is seriously hampered by the necessary small model sizes and associated small aerodynamic loads. The former renders it very difficult to diagnose the flow with adequate spatial resolution and the latter leads to poor airload measurement accuracy, resulting in a limited level of physical understanding of the underlying flow phenomena. A proof-of-concept pilot of a novel facility specifically intended for low Reynolds number testing that addresses the above problems is described. It is based on the use of a glycerine aqueous solution as the test medium, whose kinematic viscosity may be varied from 1/10 to 100 times that of air by adjusting the glycerine concentration. Super-scale models can thus be tested at the correct Reynolds number by virtue of the attainable high kinematic viscosity values. The facility is akin to a towing tank but does not have a free surface with its associated shortcomings, which is achieved by the addition of a roof with a slot through which the model support strut can move. The tank is filled to the very top and a suitable seal is used to eliminate the free surface at the slot. The seal is designed such that it allows the motion of the model support strut while remaining otherwise closed.