The impact of inlet flow conditions on the aerodynamic performance of a NACA submerged intake for ground vehicle applications

Results are presented following a series of experimental measurements on a submerged NACA type intake orientated between ±30 degrees yaw to the free stream in an atmospheric boundary layer wind tunnel at a unit Reynolds number of nominally 1 x 106. The intake was subjected to a range of upstream wall boundary layer conditions and the intake mass flow (as measured by an orifice plate) was monitored to assess aerodynamic performance. The mass flow data is supported by qualitative flow visualisation within the duct, using a smoke filament illuminated in a laser light sheet in order to gain insight into the flow physics. Intake performance, expressed in terms of a non-dimensional flow momentum coefficient, is seen to degrade with both: (i) intake orientation to the free stream - changes of nominally 40% are seen for the angle range tested and (ii) increase in upstream boundary layer displacement thickness - changes of nominally 30% are seen for the range tested. This data is presented as a graphical carpet plot, it is intended that this be used as a guide to performance prediction in non-aeronautical applications where there are often significant changes in both local flow direction and boundary layer thickness. Flow visualisation studies show that the intake performance degradation with yaw angle can be attributed to a progressive change in the vortex- pair structure within the intake as the local flow angle is increased. An increase in both lateral separation and size of the respective vortex cores is considered to act so as to reduce the magnitude of the induced inflow into the intake.