Title: EXPERIMENTAL INVESTIGATIONS ON AERODYNAMIC CHARACTERISTICS OF A HATCHBACK MODEL CAR USING BASE BLEED
Abstract: Wind tunnel tests have been conducted on a realistic hatch back car model, to investigate drag reduction opportunities from injecting low velocity air into the base region. Various techniques to reduce the aerodynamic drag of bluff bodies through the mechanism of base pressure recovery have been investigated. The investigation is conducted in free stream and in ground proximity. It is shown that, with a base bleed hose, the overall body drag is reduced. The paper shows the method used in creating the scaled model of the car and conducting the analysis, and presents the findings to date. The paper shows that the reduction in drag increases as the mass flow rate of air is increased when the flow is deflected at the outlet. By controlling the turbulent wake to the rear of the vehicle. It has been shown that base bleed can significantly decrease drag when applied to the geometry of a real hatch back model car, For the geometry studied, a bleed outlet applied to the lower portion is most effective in reducing drag. Thus the reduction in drag improves the fuel economy. The paper also discusses the feasibility of base bleed being applied to a production vehicle. for positive values of the integrand. The main reason that fuel is consumed in an automobile is to provide this tractiveenergy. Writing an equation for instantaneous fuel consumption, integrating it over a total driving duration, and using the mean-value theorem to introduceappropriate averages for some of the integrands, the followingfundamental equation for the average fuel- consumed-per-unit-distance traveledĝcan be obtained (Sovran 1983): where k is a fuel-dependent constant, ηb is the average engine efficiency during propulsion, ηdis the average drive train efficiency, S is the total distance traveled, EAcc is the energy required by vehicle accessories, and gu is the fuel consumption during idling and braking. The impact of drag on total vehicle fuel consumption therefore depends on the relative magnitudes of these contributions. Ingeneral, this coefficient is vehicle as well as driving-schedule dependent (Sovran 1983), but for the midsize car being considered they are ≈ 0.14and ≈0.46 for Urban and Highway, respectively. For the Euro mix cycle, a typical influence coefficient for cars powered by spark-ignition enginesis ≈0.3, while for diesel engines it is ≈0.4 (Emmelmann 1987b). In allcases, these values presume that the drive train gearing is rematches so that the road load power-requirement curve runs through the engine'sbrake-specific-fuel-consumption map in the same manner at the lower dragas at the higher drag. If no other changes are made in a vehicle, the benefits of reduced drag are actually threefold: reduced fuel consumption, increased acceleration capability, and increased top speed. When maximum fuel-economy benefit is the objective the increased acceleration and top-speed capabilities can be converted to additional reductions in fuel consumption. Conversion of the increased acceleration capability is accomplished by regearing the drivetrain, as discussed above. Conversion of the increased top speed requires a reduction in installed engine power, and a corresponding percentage reduction in vehicle mass so that the acceleration capability of thevehicle is not diminished. The preceding discussions have presumed the absence of ambient wind while driving. In the presence of wind a vehicle's wind speed is generally different than its ground speed, and its yaw angle is generally not zero. This affects the operating drag force, and therefore vehicle fuel economy (Sovran 1984). On the average, the result is a reduction in fuel economy.
Publication Year: 2015
Publication Date: 2015-01-01
Language: en
Type: article
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