A flow analysis for a turning rapid diffuser using CFD

In this study, a new turning rapid diffuser has been developed using CFD analyses. Typically the diffuser angle should be less than seven degrees, to avoid flow separation. This angle requirement cannot be satisfied when the diffuser length is restricted, such as in the design of a wind tunnel circuit, as a result of its overall dimension. A parametric investigation using ANSYS CFX 10 has found that the diffuser angle can be much larger, without creating flow separation, when the flow is diffused in a circular turning path. With this turning rapid diffuser, the flow has been shown to attach to the diffuser’s sidewalls, even when the diffuser angle is as large as 12 degrees. Flow separation still occurs from the inner surface in the turning direction, however further CFD analyses have indicated that this separation can be reduced by the addition of guide vanes along the turning flow path. The CFD results have been validated with a physical model before being used successfully in the construction of a closed circuit boundary layer wind tunnel at the Institute of Building Science and Technology (IBST) in Vietnam