Pressure Drop and Flow Characteristics in a Diffuser with a Dimpled Tube

Abstract

The pressure drops and flow characteristics in a diffuser fitted with a semi-dimpled tube are numerically studied. Air is selected as a working fluid and its physical properties are modelled using pressure and velocity distribution. The study reveals that every semi-dimple acts as a vortex generator. They provide the flow with intensive vortices between the dimpled surface and the diffuser wall. Therefore, they cause an enhancement in the pressure drop inside the diffuser. The performance of the dimples consisting of sphere type dimples with 5 mm in diameter. Three “Reynolds number” operated in the range of 25000 ˂Re˂ 50000 that is based on the hydraulic diameter of the diffuser Dh. The variation in Reynolds number is examined to further investigations of the pressure drop and flow characteristics of the diffuser. The numerical simulations are conducted using incompressible steady-state Reynolds Averaged Navier Stokes equations and the turbulence model “RNG k-e is utilized in the current study. The flow characteristics of the diffuser with semi-dimpled tube are analysed and compared in terms of pressure contour, velocity profile, and velocity vectors, at the operating range of Reynolds numbers. The results are discussed to point out the flow structure mechanisms. It is found that equipping the diffuser with a semi-dimpled tube leads to an increase in the recirculation and vortices inside and near the dimples area. Therefore, they have a considerable influence on the flow field. For the diffuser equipped with a semi-dimpled tube, it is noted that the flow characteristics depend on the Reynolds number. The pressure drop in the flow direction becomes lower with increasing Reynolds number. The findings indicate that for the semi-dimples, increasing Reynolds number increases the velocity distribution significantly due to better mixing of the air.

Analysis of Boosting Engine Torque and Horsepower via Diffuser Installation on the Exhaust Pipe

“…A diffuser is a device used to decrease flow velocity [12,13]. In certain occurrences, the diffuser can improve the performance of a cycle or mechanism, such as in the research of Askari and Wisnoe [14], who found in their study on pressure drop and flow characteristics that the addition of a diffuser with semi-circular protrusions on its inner profile can increase recirculation and eddies in the interior around the dimple. McLaughlin et al [15] found that varying a vaned diffuser with a diverging endwall concept can reduce the high-Pressure Ratio (PR) centrifugal compressors' dimensions without sacrificing performance.…”