Slipstream

Source: Wikipedia, the free encyclopedia.
This article is about the physical phenomenon. For other uses, see Slipstream (disambiguation).
Seed dispersal by the slipstream of a passing car.

A slipstream is a region behind a moving object in which a

velocities comparable to that of the moving object, relative to the ambient fluid through which the object is moving.[1] The term slipstream also applies to the similar region adjacent to an object with a fluid moving around it. "Slipstreaming" or "drafting
" works because of the relative motion of the fluid in the slipstream.

Overview

A slipstream created by

aerodynamic an object is, the smaller and weaker its slipstream will be. For example, a box-like front (relative to the object's motion) will collide with the medium's particles at a high rate, transferring more momentum from the object to the fluid than a more aerodynamic object. A bullet-like profile will cause less turbulence and create a more laminar flow
.

A tapered rear will permit the particles of the medium to rejoin more easily and quickly than a truncated rear. This reduces lower-pressure effect in the slipstream, but also increases

skin friction
(in engineering designs, these effects must be balanced).

Slipstreaming

The term "slipstreaming" describes an object travelling inside the slipstream of another object (most often objects moving through the air though not necessarily flying). If an object is following another object, moving at the same speed, the rear object will require less power to maintain its speed than if it were moving independently. This technique, also called drafting can be used by bicyclists.

  • Following in the slipstream of another motor vehicle, or "drafting", allows for significantly improved fuel efficiency due to reduced atmospheric drag. Truck convoys are a common example, travelling highways in a single-file queue several vehicles long. In tests, this has been shown to produce significant fuel savings.[2] Auto racing drivers also draft in order to conserve fuel, the better to gain competitive advantage by reducing the frequency of fuel stops or, more often, to reach a higher speed before pulling out to attempt to overtake another driver for example, a driver tries to overtake the leading driver so he follows the rear of the leading driver, the rear driver will gain slipstream causing the whole vehicle to gain more speed than the leading driver.
  • A related effect used for
    induced drag caused by wingtip vortices has been tested for aircraft, and could save 10%–29% fuel.[4][5][6]

Spiral slipstream

yaw nose-left at low speed and full throttle (in centerline tractor aircraft with a clockwise-rotating propeller.) This effect is caused by the slipstream acting upon the tail fin of the aircraft: The slipstream causes the air to rotate around the longitudinal axis of the aircraft, and this air flow exerts a force on the tail fin, pushing it to the right. To counteract this, some aircraft have the front of the fin (vertical stabilizer) slightly offset from the centreline so as to provide an opposing force that cancels out the one produced by the slipstream, albeit only at one particular (usually cruising) speed, an example being the Hawker Hurricane fighter from World War II
.

Propeller slipstream causes increased lift by increasing the airspeed over part of the wings. It also reduces the stall speed of the aircraft by energizing the flow over the wings.[7]: 61 

See also

Look up slipstream in Wiktionary, the free dictionary.
  • Drafting or slipstreaming as used in sports such as cycling and motor racing
  • Peloton

References

Specific references
  1. ^ Recent studies of Train Slipstreams by Johnson, Dalley, and Temple
  2. ^ Konvoi – Development and examination of the application of electronically coupled truck convoys on highways Aachen University study 2012 Archived 2014-04-14 at the Wayback Machine
  3. ^ Drag Reduction from Formation Flight. Flying Aircraft in Bird-Like Formations Could Significantly Increase Range; Defense Technical Information Center; April 2002; Retrieved February 27, 2008
  4. ^ NASA SKY SURFING FOR FUEL ECONOMY Archived 2011-04-18 at the Wayback Machine
  5. ^ Cooney, Michael (October 11, 2012). "Air Force lab tests out "aircraft surfing" technique to save fuel". Network World.
  6. US Air Force. Archived from the original
    on 12 December 2012. Retrieved 23 November 2012.
  7. ISBN 0903083019
    .
General references
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