Reduction of Aerodynamically Undesirable Influences Due to Engine Cooling Flow in Road Vehicle

The purpose of this research is to clarify causes for the change in aerodynamic characteristics of a road vehicle model due to engine cooling flow in wind-tunnel experiments with the moving-belt ground board, in order to propose methods to reduce the drag and lift. With regard to engine cooling flow, the air-intake system was adjusted with variable opening area and position for the engine loading system of FF and FR with and without a radiator. A simplified 1/5 scale vehicle model was manufactured with transparent externals around the engine for flow visualization. The overall results show that with enlargement of the opening area, the drag and the front lift increased and the rear lift decreased. The flow visualization and the measurements of underfloor velocity and surface pressure indicated the cause of the characteristics changes. Enlargement of the opening area causes flow disturbance by merging of the scavenging flow and the underfloor flow, which has blockage effects for the upstream of each flow with keeping high pressure in the engine compartment and causes pressure loss under the floor behind the engine unit. The difference between the two engine loading systems lies indirection and location of the engine unit, which causes the differences of how the flow features affect the aerodynamic characteristics. The effect of the radiator is to reduce the range of changes in drag and lift. Finally, it is discussed that the principle of reducing drag and lift is to suppress interference of scavenging flow, and concrete methods are proposed.

Attenuation Effect of Expansion Configuration and Acoustic Material on Propagation of Blast Waves in a Duct

With recent increase of cars, the noise problem has been caused by the exhaust sounds released from exhaust pipes, which consist of weak and pulsed shock waves called blast waves. To diminish the noise, a silencer is set up in front of the exhaust pipe. In the present study, reflectors were installed in the high-pressure section of the shock tube to generate blast waves, and three types of expansion region were investigated, combined with acoustic material of glass wool. The pressure decay was evaluated by transmission factor and reflection factor for the incident blast wave, together with pressure histories and high-speed Schlieren photography. As results, it was confirmed that the acoustic material greatly contributed to blast-wave attenuation: the one stage expansion model with glass wool recorded the highest decay of the peak over pressure for transmission, and other models with glass wool showed the second highest. The acoustic material also contributed to decay of reflected shock waves propagating toward an upstream duct.