Abstract
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.
Highlights
The pressure on the engine bottom increases and so does the pressure at the frontward side, which is considered to be connected with the pressure on the front end of the vehicle body, and the pressure on the front window increases (Figure 16(b)); the drag increase is considered to be due to high pressure on the front end and front window of the vehicle body induced by high pressure inside the engine compartment
The test model was designed to simulate the engine cooling flow that can be applied to almost all domestic vehicle types with a front engine by simplifying common items, and for change of intake opening area the changes of aerodynamic characteristics were investigated with variation of the intake position and the two engine layout of width and length placements in presence or absence of the radiator
It is considered that the tendency of change in drag and lift is universally applicable to real road vehicles without separation at the rounded front end, but with lower drag
Summary
In order to realize further reduction of aerodynamic drag, attention has focused on reduction of the shape drag and the internal-flow drag. It is generated mainly when the wind blows through the front air intake to the engine compartment for cooling a radiator, an air-conditioning condenser and an engine itself. The internal-flow drag through an engine compartment occupies about 10% of the whole aerodynamic drag, and today when the shape of the car body has improved, the reduction of the cooling-flow drag begins to be put into emphasis
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