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.

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 the curve diffuser is greatly affected by the abrupt expansion and inflection introduced, particularly when a sharp 90o curve diffuser is configured with a high area ratio (AR). Therefore, the paper aims to numerically investigate the effect of the expansion direction of AR=1.2 to 4.0 curve diffuser on loss characteristic and flow rectification. 90o curve diffuser operated at inflow Reynolds Number, Rein=5.934 × 104 to 1.783 × 105 was considered. Results show that pressure recovery improves when the area ratio increases from 1.2 to 2.16 for both 2D expansion (z- direction) and 3D expansion (x- and z- direction). On the other hand, the increase of inflow Reynolds number causes the flow uniformity to drop regardless of the expansion directions. 3D expansion (x- and z- direction) curve diffuser with AR=2.16, operated at Rein=8.163 × 104, is opted as the most optimum, producing the best pressure recovery up to 0.380. Meanwhile, 2D expansion (z-direction) curve diffuser of AR=2.16, , operated at Rein= 5.934 × 104, is chosen to provide the best flow uniformity of 2.330 m/s. 2D expansion (x- direction) should be as best avoided as it provides the worst overall performance of 90o curve diffuser.