Let's say you want to predict the aerodynamic drag of a new car based on the use of a model that is one- fifth scale of the actual car/prototype car. We want to predict the drag of the car when it has wind velocity 75 miles/hour with an air temperature of 40°C. The model is placed in a wind tunnel at 10°C. Determine the wind tunnel velocity necessary to achieve similarity between the model and the prototype.

Let's say you want to predict the aerodynamic drag of a new car based on the use of a model that is one- fifth scale of the actual car/prototype car. We want to predict the drag of the car when it has wind velocity 75 miles/hour with an air temperature of 40°C. The model is placed in a wind tunnel at 10°C. Determine the wind tunnel velocity necessary to achieve similarity between the model and the prototype.

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter6: Forced Convection Over Exterior Surfaces

Section: Chapter Questions

Problem 6.32P

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The aerodynamic drag of a new sports car is to be predicted at a speed of 60.0 mi/h at an air temperature of 25°C. Automotive engineers build a one-third scale model of the car to test in a wind tunnel. The temperature of the wind tunnel air is also 25°C. The drag force is measured with a drag balance, and the moving belt is used to simulate the moving ground (from the car’s frame of reference). Determine how fast the engineers should run the wind tunnel to achieve similarity between the model and the prototype.
(b) A wind-tunnel experiment is performed on a small 1:5 linear-scale model of a car, in order to assess the drag force F on a new full-size car design. A dimensionless "drag coefficient" Ca is defined by C, =- pu'A where A is the maximum cross-sectional area of the car in the flow. With the model car, a force of 3 N was recorded at a flow velocity u of 6 m s. Assuming that flow conditions are comparable (i.e., at the same Reynolds number), calculate the expected drag force for the full-sized car when the flow velocity past it is 31 m s (equivalent to 70 miles per hour). [The density of air p= 1.2 kg m.]
The aerodynamic drag of a new sports car is to be predicted at a speed of 60 mph at an air temperature of 25°C. Automotive engineers build a one-third scale model of a car to test in a wind tunnel, shown in the figure below. The temperature of the wind tunnel air is also 25°C. The drag force is measured with a drag balance, and the moving belt is used to simulate the moving ground (from the car's frame of reference). The aerodynamic drag on the model in the wind tunnel is measured to be 34.5 lbf when the wind tunnel is operated at the speed that ensures similarity with the prototype car. Estimate the drag force (in lbf) on the prototype car at the given conditions. For air at T = 25°C and atmospheric pressure, p=1.184 kg/m3 and u-1.849-10-5 kg/m-s. Wind tunnel test section Pm Pm Fo.m Moving belt Drag balance The drag force on the prototype car is estimated to be Ibf.
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