1. Scope--This SAE Information Report has been prepared by theStandards Committee on Cooling Flow Measurement (CFM) at the request ofthe SAE Road Vehicle Aerodynamics Forum Committee (RVAC). The committeewas formed in January 1985 for the purpose of investigating whatmeasuring techniques are used by automotive product manufacturers todetermine air cooling air flow rates and, if possible, to synthesizethese into a recommended practice report.

Although a great deal is already known about engine cooling, recentconcern with fuel conservation has resulted in generally smaller airintakes whose shape and location are dictated primarily by low vehicledrag/high forward speed requirements. The new vehicle intakeconfigurations make it more difficult to achieve adequate cooling underall conditions. They cause cooling flow velocity profiles to becomedistorted and underhood temperatures to be excessively high. Suchproblems make it necessary to achieve much better accuracy in measuringcooling flows.

As the following descriptions show, each company or institutionconcerned with this problem has invested a lot of time and as a resultgained considerable experience in developing measuring techniques thatappear to achieve reliable results. There is, however, littleuniformity at the present time among the methods used by differentcompanies and no indication at this time of a trend towards a simpleand universally acceptable measuring technique. If one can makegeneralizations, it seems that the North American industry appears touse vane anemometers, whereas the European industry appears to favorpressure measurements for determining cooling air flows.

Usually cooling flow measurement makes use of ensemble averagecalibrations of arrayed sensors. The major drawback of ensembleaveraging usage of sensors appears to be the need for prior calibrationof each combination of sensor array and radiator/vehicle front-endconfiguration. While there appears to be a growing interest in alsoknowing flow distributions--which necessitates the use of a pluralityof sensing devices--very little is made of area-averaging techniques.

Given the present state of the technology, this report covers simply anoverview of the different measuring techniques deployed in theindustry, and it is left to the future to report on developmentstowards a unified cooling flow measurement method. Appendices A and Bpresent a number of problem statements that were identified during thepresent CFM review and whose solution would promote a betterunderstanding of cooling flow measurement generally.

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