Pressure loss reduction of a Borda–Carnot sudden expansion applying a passive flow control method

The reduction of the pressure loss, applying a passive flow control method, was investigated in a three-dimensional, square cross-sectioned Borda–Carnot sudden expansion, representing a frequent element of pipe systems. The flow control elements were mini-flaps, placed on the edge of the step of the sudden expansion, forming a mini-diffuser. The angle of the mini-flaps, relative to the main flow direction, was changed, an optimum angle for reducing the pressure loss was found. The global flow parameters were determined based on static pressure measurements, while details of the velocity and turbulent intensity field were examined using Laser Doppler Velocimetry. Further analysis of the flow field, for different setups, was carried out by Reynolds-averaged Navier–Stokes computational fluid dynamic calculations. The method can be readily applied in practice with very low-investment costs and can enhance the efficiency of power generation and air conditioning systems as well.