Aerodynamic drag

Since u and 6 are functions of time, they are written u t) and 6 t). The constant a could be calculated if the following vehicle data for engine torque T, wheel traction force F, aerodynamic drag D were available ... 

Now aerodynamic drag D must equal traction force F... 

Of obvious importance to aircraft is the smoothness of exterior surfaces. Smooth aerodynamic surfaces reduce aerodynamic drag, resulting in higher airspeeds and increased efficiency. Mechanical fasteners, even countersunk flush fasteners, introduce disruptions in the airflow over the exterior surface. Even the slight deformation of thin sheets around fasteners produces drag. Adhesively bonded structure has no fasteners to disrupt airflow and is more capable of producing the smooth continuous contours that are so common on aircraft. 

This gain has not come entirely at the expense of fuel economy, however. Over that same twenty-year span, the fuel economy of the average new U.S. car increased by 80 percent. These advances are attributable to lower vehicle weight, improved tires, reduced aerodynamic drag, improved transrnissious, and gains in engine efficiency. 

The force of aerodynamic drag opposing foiward motion of the vehicle depends on its drag coefficient (Cj), its frontal area (A,), the air density (p), and the velocity of the wind with respect to the vehicle. In still air, this velocity is simply the vehicle velocity (V.). If driving into a headwind of velocity V , however, the wind velocity with respect to the vehicle is the sum of these two. Multiplying the aerodynamic drag force by vehicle velocity provides the aerodynamic power requirement (PJ. 

A major fraction of the aerodynamic drag in the modern streamlined car is caused by flow separation at the rear of the body. Alleviating that separation calls for a long afterbody that tapers to a point. 

A corresponding situation occurs at high altitude, where one-third of the sea-level power available has been lost due to low atmospheric pressure. This low air density also reduces aerodynamic drag, but rolling resistance is unaffected by altitude. As a result, power resei"ve is seen to suffer. In fact, at this altitude, the power available in fourth gear is insufficient to operate the vehicle on a 6 percent grade at any speed without downshifting. 

Sovran, G. Morel, T. and Mason, W. T., Jr. (1978). Aerodynamic Drag Mechanisms ofBluft Bodies and Road Vehicles. New York Plenum Press. 

With the exception ot avid sport and competitive use. It IS typically operated at low speeds that do not cause high aerodynamic drag. 

EMS requires about 1 to 2 kW of magnet power for evei y ton of vehicle mass. At modest and high speeds this power loss is small compared with the power loss due to aerodynamic drag. EMS is the favored approach for urban maglev and is suitable for high speeds if the use of a minimal 10 mm air gap is acceptable. 

Aerodynamic drag has also been used to capture energy from the wind. Drag mechanisms consist of flat or cup-shaped devices that turn the rotor. The wind simply pushes the device around the main shaft. Anemometers used to measure wind speed are often drag devices, as are traditional farm windmills. 

A modern VAWT that relies upon aerodynamic drag is known as a Savonius wind turbine. Sigurd Savomus, a Finnish inventor, developed this design in 1924. Two S-shaped panels are arranged to cup the... 

The total power, P, needed from a vehicle s power system must be sufficient for vehicle acceleration, aerodynamic drag losses, rolling resistance, changes in elevation, and auxiliary power for vehicle accessories (20,21). These power terms are, respectively ... 

When there is gas flow upward through the balance chamber, an aerodynamic drag force is exerted on the suspended mass. If the particle Reynolds number (Re = laV lv) is sufficiently small so that creeping flow may be assumed, Eq. (14) may be written to include the aerodynamic drag, and it becomes... 

The calibration procedure, then, is to measure voltage K for a given volumetric flow rate and calculate from the measured radius and knowledge of the gas viscosity. Note that when the flow rate is set such that no dc voltage is required to levitate the particle—that is, when the aerodynamic drag balances the weight—Eq. (33) can be used to determine the aerodynamic size, provided that the density is known. 

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