Pressure Losses in Combining Subsonic Flows Through Branched Ducts

An investigation of the “additional” total pressure losses occurring in combining flow through several sharp-edged three-leg junctions has been made. Experimental results covering a wide speed range up to choking are presented for three flow geometries of a lateral branch off a straight duct using dry air as the working fluid. A new theoretical flow model provided results in fairly good agreement with the experimental data obtained. Flow visualization of the high-speed flow using the Schlieren method revealed the presence of normal shock waves in the combined flow about one duct diameter downstream of the junction. The highest attainable Mach number (M₃) of the averaged downstream (combined) flow was 0.66 for several of the flow geometries. This value of M₃ appears to be the maximum possible and is the result of a combination of flow separation and local flow choking.