Explanation: The value of y+ depends on the distance from the wall. So, the concept of y+ is also valid only when we solve turbulent boundary layer problems. The turbulent boundary layer has different sub-layers based on this y+ value.

While the other parameters like eddy kinematic viscosity, eddy dynamic viscosity and the kinetic energy do not depend on the y+ value.

Explanation: All these laws are used in modelling turbulent boundary layers. The law of the wake depends on the function of the distance from the wall and the boundary layer thickness. It does not depend on the y+ value.

Explanation: y+ is the ratio of the product of the distance from the wall boundary and the shear velocity to the kinematic viscosity. This is given by the equation y+=y ut/ν. This is why the value of y+ increases with the distance from the wall.

Explanation: Shear velocity is used while defining the y+. It otherwise called the friction velocity. It is the square root of the ratio of wall shear stress to density. It has the same unit as that of normal velocity.

y+ (unitless and dimensionless)= \(y(m)u_t(\frac{m}{s})⁄ν(\frac{m^2}{s})\).

Explanation: For low Reynolds number turbulent models, wall function can be used to integrate the function. This wall function cannot be used if the value of y+ is not more than 30. If the value of y+ is less than 30, the wall function is invalid.

Explanation: Buffer layer has the turbulent forces and the viscous forces in equal magnitude. In this layer, the range of y+ is 5 < y+<30. 0 < y+ < 5 is for the linear or viscous sub-layer. The buffer layer lies just above the viscous sub-layer.

Explanation: 30 < y+ < 500 is the range of y+ where the value of u+ varies logarithmically with the y+ value. It is called the log-law layer. As the value 50 falls in this range, it belongs to the log-law layer.

Explanation: Though the layer varies from viscous sub-layer to buffer layer when y+ crosses the value 5, the variation is still linear. This linear variation becomes logarithmic variation when y+ crosses 11.63 to be exact.