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.

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The annular diffuser is an expansion area, which, despite its simple structure, is very important in some engineering and thermal applications. In the present research, numerical simulations were performed to investigate the temperature field and flow structure characteristics in an annular diffuser. The hub of the annular diffuser consisted of a straight semi-dimpled tube SSDT. Three different diffuser wall angles (α) 1.8˚, 3.6˚ and 5.4˚ with inlet Reynolds number 1.5 × 10 4 were studied in details with air as a working fluid. The computational fluid dynamics CFD was used to simulate the model in a turbulent flow. The standard k-ε turbulence model was used to complete the governing equations. The numerical results, mainly the temperature distribution, pressure drop and velocity distribution for the airflow in the annular diffuser fitted with SSDT for different diffuser wall angles α were obtained and compared. It was observed that as the wall diffuser angle α increases, the enhancement of the temperature distribution and the velocity distribution decrease while the pressure drop rate increases. The maximum temperature distribution and velocity distribution were completed by diffuser wall angle α 1 = 1.8˚ whereas, the highest pressure drop achieved by diffuser wall angle α 3 = 5.4˚.

Numerical analyses study is reported on the flow characteristics in a conical diffuser with a helical tape insert. In this study, a rectangular tape of 5 mm width and 2 mm thickness is used inside the inner wall of the diffuser to induce additional recirculation. The numerical results are achieved for different Reynolds numbers (58035, 116072, 174108 and 232144) based on the inlet hydraulic diameter. The simulations are carried out with constant inlet condition considering the flow turbulent and incompressible. Air is used as a working fluid and maintained at constant room temperature. From a similar inlet condition, the results indicated that the velocity distribution is well enhanced.

This paper presents an aerodynamic characteristic study in longitudinal direction of UiTM Blended Wing Body-Unmanned Aerial Vehicle Prototype (BWB-UAV Prototype) equipped with horizontal stabilizers. Flight tests have been conducted and as the result, BWB experienced overturning condition at certain angle of attack. Horizontal stabilizer was added at different location and size to overcome the issue during the flight test. Therefore, Computational Fluid Dynamics (CFD) analysis is performed at different configuration of horizontal stabilizer using Spalart - Allmaras as a turbulence model. CFD simulation of the aircraft is conducted at Mach number 0.06 or v = 20 m/s at various angle of attack, α. The data of lift coefficient (CL), drag coefficient (CD), and pitching moment coefficient (CM) is obtained from the simulations. The data is represented in curves against angle of attack to measure the performance of BWB prototype with horizontal stabilizer. From the simulation, configuration with far distance and large horizontal stabilizer gives steeper negative pitching moment slope indicating better static stability of the aircraft.