The skin friction coefficient, , is defined by: Where is the local wall shear stress, is the fluid density and is the free-stream velocity (usually taken ouside of the boundary layer or at the inlet).. For a turbulent boundary layer several approximation formulas for the local skin friction for a flat plate can be used:
Skin friction drag is caused by the viscosity of fluids and is developed from laminar drag to turbulent drag as a fluid moves on the surface of an object. Skin friction drag is generally expressed in term of the Reynolds number, which is the ratio between inertial force and viscous force.
Snorri Gudmundsson BScAE, MScAE, FAA DER(ret.), in General Aviation Aircraft Design,. 2014. Step 4: Skin Friction Coefficient for Fully Laminar or Fully Turbulent Boundary Layer. First, if the intent is to calculate the skin friction coefficient assuming a mixed boundary layer go to Step 5. Otherwise, decide whether to treat the boundary layer as either fully laminar or fully turbulent.
Skin friction follows the drag equation and rises with the square of the velocity. Skin friction is caused by viscous drag in the boundary layer around the object. There are two ways to decrease skin friction: the first is to shape the moving body so that smooth flow is possible, like an airfoil.
Hence, as far as it appears from the relation the Reynold no. is multiplied to the skin friction coefficient either to amplify or reduce effect of skin friction. To fit the value to scale of interest.
It must be noted, the skin friction coefficient is equal to the Fanning friction factor.The Fanning friction factor, named after John Thomas Fanning, is a dimensionless number, that is one-fourth of the Darcy friction factor.As can be seen, there is a connection between skin friction forces and frictional head losses.. See also: Darcy Friction Factor ...
Friction is a resistive force that opposes an object's motion or intended motion. The formula to compute the frictional force (f) isf = µN. The coefficient ( µ) is unique for different materials. The normal force (N) is the countering force that the surface exerts on the object to oppose its weight.We proceded as follows:
The variation in turbulent flat plate skin friction coefficient with Reynolds number is calculated below. This is used when compiling an estimation of aircraft parasitic drag as described in the tutorial on the Drag Polar. The skin friction is graph originally published in USAF Stability and Control Datcom and reproduced in Roskam Part VI Chapter 4.2 .
This relation shows that the drag coefficient of the body can be obtained if the ~11pmentunlarea of the wake. far downstream can be calculated. If TO is the skin friction at a point of the surface of the body and r the local radius of cross section the skin friction drag coefficient of the body Cf is given by 1 Cf = iJeJ 0 2 ·2nr.d~, (5) ()
The skin-friction coefficient is independent of wind speed except where the wind modifies the underlying surface, for example, a sheet of water or field of tall grass. It appears to be independent of thermal stability and, over a fully rough surface, of the wind speed at the reference level, but it does depend on the height of the reference level.. Values derived for the atmosphere have almost ...