Dear Mr Chomachar.

You wrote:

"From fluid dynamics, I know boundary-layer is an imaginary hypothesis, adopted for finding velocity profile over flat plate"

Not only boundary layers are mental invention: the same is turbulence, vortices and other flow components having no mathematical definition and physical confirmation.

But there is another way based on analysis of the fundamental equations set.

On this way the first step is definition of the fluid medium and physical parameters describing its flow (that are density, momentum, complete energy and constituents impurities).

Classification of flows components based on complete solutions of the linearized equations set includes waves and ligaments. Vortices are product of non-linear interactions of basic flow components.

If look in papers on my ResearchGate page you can learn more about fundamental and scale invariant fluid mechanics in general and examples of calculations and observations of flows on a flat plate.

Sincerely,

Yuli D Chashechkin

Hello dear Saeb, check out the attached documents and link, it is a technique which is applied for boundary layer control to delay the separation to enhance the performance of the airfoil... Thanks

https://www.youtube.com/watch?v=w1Q6-NJPpkk

https://www.sciencedirect.com/search?qs=boundary-layer%20suction&show=25&sortBy=relevance

It is a kind of boundary layer used for fluid dynamics problems dealing with suction.

https://www.youtube.com/watch?v=w1Q6-NJPpkk informative and very useful. Thanks Ahmed S. Mansour.

Dear Mr Chomachar.

You wrote:

"From fluid dynamics, I know boundary-layer is an imaginary hypothesis, adopted for finding velocity profile over flat plate"

Not only boundary layers are mental invention: the same is turbulence, vortices and other flow components having no mathematical definition and physical confirmation.

But there is another way based on analysis of the fundamental equations set.

On this way the first step is definition of the fluid medium and physical parameters describing its flow (that are density, momentum, complete energy and constituents impurities).

Classification of flows components based on complete solutions of the linearized equations set includes waves and ligaments. Vortices are product of non-linear interactions of basic flow components.

If look in papers on my ResearchGate page you can learn more about fundamental and scale invariant fluid mechanics in general and examples of calculations and observations of flows on a flat plate.

Sincerely,

Yuli D Chashechkin

@ Saeb AmirAhmadi Chomachar

Dear Saeb

In the domain of aerospace and aviation, the existence of flow separation leads to the instability of flying vehicles, the generation of noise, increasing of drag and the reduction of lift. The flow separation control technology has been gradually developed as an important branch of mechanics. Flow control methods are divided into passive, which require no auxiliary power and no control loop, and active, which require energy expenditure. Boundary-layer suction is one the important method of active flow control methods.

It is a flow control technique for delaying boundary layer separations. Based on the technique, the conception of aspirated compressor was provided to increase the blade loading and to decrease the flow loss. In addition, in the wind tunnel test, boundary layer suction is used to improve the quality of inlet flow.

The boundary layer concept describes a real phenomenon: In attached flow, the velocity of the flow near the airfoil (which is zero at the the airfoil surface, at least in 2D flow)increases to the free stream velocity. Since this is asymptotic, there is no real boundary layer thickness, but there are integral values (like momentum loss thickness, or displacement thickness) that allow for description. Boundary layers may become unstable (eg transition from laminar to turbulent, or flow separation). So, techniques were develop to either add energy to the boundary layer, or remove low energy portion of air from the boundary layer, to prevent separation.

In summary, suction is the force being exerted on the fluid flow. Within the thin boundary layer where the effect of viscosity is highly significant, suction and injection are two major factors that can influence the dynamics.

Thank you all.