Flow in diffusers

The flow behavior in simple diffusers is treated from a view-point of flow stability, and an important parameter to be included for internal flow analysis is proposed. Thereafter, the feature of the new parameter at the critical condition of diffuser stall is examined by comparing many experimental data in the literature with prediction based on a conventional boundary layer theory. As a result, the role of the parameter for flow separation is clarified and the parameter is nicely incorporated in a conventional boundary layer calculation method for internal flow. Furthermore, the modified theory is applied to a few cases of decelerating flow, and the predicted separation points and pressure distribution along the wall are compared with experimental data.