Development of subsonic curved diffuser performance correlations integrated angle of turns using asymptotic computational fluid dynamics

Numerous studies on the performance of the curved diffuser have been made on either 2-D or 3-D expansion type with various working geometrical and operating parameters. Most researchers are focusing in the existence of flow separation phenomenon and secondary flow vortices that often disturb the recovery of pressure and uniformity of flow. On top of that, the existing guideline have just integrated the geometrical and operating effects in a low range. Therefore, the current work focussing on studying the effects of a wider turning angles in a range of 30° to 180° integrated with various operating condition by experiment and numerical method. The experimental rig was built at Aerodynamics Laboratory, UTHM. The blower speed was set in range of 9RPM-25RPM and tested for 30°, 90° and 180° curved diffusers. A profound set of R

Effect of inner wall curvature on loss characteristic and flow rectification of curved diffuser

A curve diffuser is frequently used in applications such as HVAC, wind tunnel, gas turbine cycle, aircraft engine, etc., as an adapter to join the conduits of different cross-sectional areas or an ejector to decelerate the flow and raise the static pressure before discharging to the atmosphere. The performance of a curve diffuser is measured according to its pressure recovery and flow uniformity. The paper aims to investigate the effect of inner wall curvature numerically and inflow Reynolds number on loss characteristic, and flow rectification Ansys FLUENT was used to simulate the performance of curved diffuser in terms of static pressure coefficient and flow uniformity index by altering the inner wall curvature (Lin/W1 = 1.52, 3.99, 8.99, 13.00 and 25.00) and inflow Reynolds number (Rein= 5.9343 × 104 , 8.1628 × 104 and 1.783 × 105 ). The results show that pressure recovery improved when the inner wall curvature increased from 1.52 to 8.99 for a curved diffuser with an area ratio of 1.6, 2.16, and 4.0. Meanwhile, the increase of inflow Reynolds number caused the flow uniformity to drop at every area ratio of the curved diffuser. The model of the curved diffuser with inner wall curvature of 8.99 and area ratio 4.0 opted as the most optimum producing best pressure recovery up to 0.40 operated at Rein= 5.9343 × 104 . Meanwhile, the model with inner wall curvature of 25.00 and area ratio 4.0, operated at Rein = 5.9343 × 104 , was chosen as the best flow performance with an index of 1.92

Effect of Employing Vortex Generator on Curve Diffuser Performance

A diffuser is commonly applied in fluid-flow engineering applications with its simplest form of expanding area in the flow direction. A curve diffuser is one of its kinds often associated with secondary flow separation, thus improvement via installing passive flow control devices such as a vortex generator is to explore. The present work aims to numerically investigate the potential of four (4) types of vortex generators, i.e. triangle, rectangle, tapered, wishbone to improve the 90° curve diffuser performance. The results suggest that using vortex generators on a curve diffuser can improve performance. Triangle vortex generator provides the most optimum pressure recovery and flow uniformity of respectively 0.250 and 2.14.  This promises improvement of approximately 31.3% and 25.4% relative to the benchmark case, without vortex generator

Effect of angle of turn on loss characteristics and flow rectification of curve diffuser

Curve diffuser is often used in HVAC and wind tunnel systems to provide pressure recovery and avoid excessive energy loss to the surrounding environment. Performance of curve diffuser is disturbed mainly by the presences of flow separation and secondary flow vortices occurred due to the effect of turning angle, in which scarce literature found. In this study, the effect of turning angle from 30° to 180° configured with an area ratio of 1.60 to 4.00 and inflow Reynolds number of 5.934x104 – 1.783x105 on loss characteristics and flow rectification of curve diffuser is investigated with optimum configuration is proposed. Performance of curve diffuser is evaluated in terms of pressure recovery and flow uniformity using ANSYS CFD equipped with validated Standard k-ɛ model (ske) and enhanced wall treatment of y+ = 1.2 - 1.7. Results show that performance of pressure recovery and flow uniformity decreases respectively by 85.71% and 45.84% as the angle of turn increases from 30° to 180°. Curve diffuser with minimum angle of turn 30o , optimum area ratio 2.16 and intermediate Rein 8.163x104 turns out to be the best configuration to provide pressure recovery of 0.399 and flow uniformity of 3.630 m/s

Effect of turbulence intensity on turning diffuser performance at various angle of turns

The performances of turning diffuser are highly affected due to the nature of its geometries by the existence of flow separation and dispersion of core and secondary flows. Turning diffusers with potential turbulence intensity may lead to optimum performance. However, there has been yet insufficient literature on 3-D turning diffuser fluid flow performance analysis by varying inlet turbulence intensity. Hence, this study aims to investigate the effect of turbulence intensity on 30o and 90o 3-D turning diffuser performances. The performances of turning diffusers were scientifically evaluated in term of pressure recovery coefficient, Cp and flow uniformity index, σout while turbulence intensity was varied from 1.5% to 7.5%. This work involved both numerical and experimental methods. ANSYS Computational Fluid Dynamics (CFD) was used for the simulation and Particle Image Velocimetry (PIV) for the experiment. The inlet free-stream turbulence intensity was varied which imposed on the flow by suppressing the separation of the inner wall boundary layer and mixing to provide optimum uniformity of the flow. The pressure recovery increased 8.02% and 9.74% while the flow uniformity improved about 2.95% and 1.60% in 30° case and 90° case respectively. In conclusion, the 7.5% of turbulence intensity is promising to introduce in the ducting flow application so as to improve the pressure recovery and the flow uniformity of both 30° and 90° turning diffuser cases