Drag coefficient and Reynolds' Number. ```Name: anthony Status: N/A Age: N/A Location: N/A Country: N/A Date: Around 1993 ``` Question: I am dealing with a project which tested scale models of a series of automobiles and I found the optimum air speed (air speed that gave lowest drag coefficient). I also found the rate of change of the drag coefficient with respects to the air velocity. How can I explain why this happened. For example, my drag coefficient dipped at 28 m/s and then skyrocketed beyond that speed. Someone told me that the Reynolds' number might help me to explain the cause for the optimum air velocity to be a specific speed and nothing else. I am not really familiar with the Reynolds' number. All I know about it is that it can tell you if you have laminar or turbulent flow. I know that it is VERY important in aeronautical research and engineering. Please explain its significance if that is the solution to my problem. Replies: That someone may be right. Reynolds' discoveries probably apply here. Osborne Reynolds found that there were two types of viscous flows in pipes. At low velocities, the fluids acted with laminar flow properties, and they matched the analytical predictions. At higher velocities, however, the flow breaks up into fluctuating velocity patterns or eddies (turbulent flow) in a form that has not yet been fully predicted. Quite a bit of study has been done on these properties recently. Reynolds also established that the transition from laminar to turbulent flow was a function of a single number, called the Reynolds number. It is a product of the velocity, fluid density, and pipe diameter, divided by the fluid viscosity. If that number is less than 2100, the flow will always be laminar. When it is higher than 2100, it will NORMALLY be turbulent. This can be controlled, however. Another factor is boundary layer theory, which through the work of Prandtl, von Karman and von Mises, have greatly simplified the Navier-Stokes equations and included the effects of boundary layer and inviscid fluids outside the boundary layer. dipper Click here to return to the Engineering Archives

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