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The use of Shadowgraph and Schlieren optical systems is a simple method to determine flow patterns of heated air external to the vehicle at idle. In particular, the method can be used to visualize natural convective air flow patterns at the underbody to aid in heat shielding design. Moreover, air recirculation patterns around the front end of the vehicle can be visualized without the use of smoke. The optical equipment is described and recommendations proposed for setting up the equipment. A video tape of some results is also presented.

Optimizing heat protection for underbody and underhood components, using non-CFD heat transfer CAE tools, requires the estimation of local convective heat transfer coefficients. This estimate, in turn requires knowledge of the local air velocity. Currently available methods for obtaining this velocity at several vehicle locations have been impractical and expensive for use in over-the-road testing. This paper presents the design, fabrication, and field testing results of a 26 mm diameter spherical transducer which measures the local heat transfer coefficient directly. The transducer contains three thermocouples and a heater. It is calibrated to correlate the coefficient with the air velocity. Drawing less than 0.1 A, a number of them can be powered by the vehicle battery with negligible drain. The data acquisition consists of sampling three thermocouples per spherical transducer.