Effect of the external parallel acoustic excitation on the adverse pressure gradient (APG)‎

الملخص EN

There was a needed for a technique to be able to enhance the flow properties by decreasing the velocity in (APG) Adverse Pressure Gradient and increasing the skin friction .The present work used a technique of the effect of external parallel acoustic excitation on the Adverse Pressure Gradient (APG) over a rough surface and smooth surface for a turbulent flow.

This study was conducted at fully developed turbulent flow with a Reynolds number based on hydraulic diameter (8.3×104).

The experimental ducts test carried out in wind tunnel manufactured from Perspex (250mmx250mm) and length of 690 mm .

A Preston tube was used to measure the air flow velocity profile, pressure distribution and skin friction.

The adverse pressure gradient was produced in unsymmetrical diffuser with three different diffuser angles (8, 11,and 15) degree.

The external excitation was parallel to the flow , and the excitation frequency (150) Hz and SPL (95 ) dB were used in this study .

The obtained results showed that the performance, and other flow characteristics of diffusers depend on the angle of diffuser and acoustic excitation, and indicated that the surface roughness enhanced the production of turbulence as well as the turbulence level when compared with the smooth-wall data.

It is well known that both wall roughness and APG reduce the mean velocity close to the wall.

The rough surface with the external parallel excitation effect are regarded as the key parameters to enhance the flow characteristics, this technique is able to decrease the velocity and increase the skin friction and to enhance the flow properties and thus improve the flow structure.

Kay words ; parallel external excitation , wind tunnel , at fully developed turbulent , flow velocity profile, pressure distribution ,skin friction .