Boundary Layer Theory: New Analytical Approximations with Error and Lambert Functions for Flat Plate without/with Suction

In this work, we investigated the problem of the boundary layer suction on a flat plate with null incidence and without pressure gradient. There is an analytical resolution using the Bianchini approximate integral method. This approximation has been achieved by Lambert or Error functions for boundary layer profiles with uniform suction, even in the case without suction. Based on these new laws, we brought out analytical expressions of several boundary layer features. This gives a necessary data to suction effect modeling for boundary layer control. To recommend our theoretical results, we numerically studied the boundary layer suction on a porous flat plate equipped with trailing edge flap deflected to 40°. We showed that this flap moves the stagnation point on the upper surface, resulting to avoid the formation of the laminar bulb of separation. Good agreement was obtained between the new analytical laws, the numerical results (CFD Fluent), and the literature results.

Approximate Solutions of the Unsteady Boundary-Layer Equations

An approximate integral method is proposed for solving the unsteady laminar boundary-layer equations. The essence of the method is to assume a similar solution for the velocity profile even in those situations where similar solutions do not exist, and then to find a suitable scale function for the similarity variable. The scale function is the solution to a simple first-order linear partial differential equation. This solution is determined in closed form. Satisfactory results were obtained in comparison with more sophisticated and time-consuming procedures.

Combined Forced and Free Convection Laminar Flow over a Vertical Plate

The approximate integral method of von Kármán is adapted to analyse combined forced and free convection laminar flow over a vertical flat plate at a constant temperature. This approach produces relatively simple expressions relating velocity and temperature profiles, skin friction and heat transfer to Pr and Gr/Re2 for the situation where forced convection flow is dominant over free convection. The results of the analysis compare favourably with more exact theoretical treatments and with experiment.

Combined Forced and Free Convection Laminar Flow over a Vertical Plate

The approximate integral method of von Kármán is adapted to analyse combined forced and free convection laminar flow over a vertical flat plate at a constant temperature. This approach produces relatively simple expressions relating velocity and temperature profiles, skin friction and heat transfer to Pr and Gr/Re2 for the situation where forced convection flow is dominant over free convection. The results of the analysis compare favourably with more exact theoretical treatments and with experiment.