An investigation into the scaling law of converging length for compressible round twin-jet

An experimental investigation has been conducted to develop the scaling law for the converging length of compressible round twin-jets. A twin-jet system with nozzle exit diameter D and normalized inter-nozzle spacing S/D of 3, 4, and 5 was investigated at ideally expanded jet Mach numbers M-j of 0.3, 0.5, 0.7, 1.0, 1.35, and 1.56. Scaling analysis performed for the converging length x(cp) revealed that the relationship x(cp)/D = g(1) (M-j, S/D) could be reduced to x(cp)/(S-1.8/D-0.8) = g(2)(M-j), where g(1) and g(2) are different functions. This scaling law extended to include both perfectly and imperfectly expanded sonic and supersonic twin-jets, leading to the relation x(cp)/(S-1.8/D-0.8), is proportional to (gamma M(j)(2)p(e)/p(a))(1/(jc+1)), where p(e)/p(a), gamma, and j(c) are the nozzle expansion ratio, gas specific heat ratio, and index number, respectively. It has been documented that S-1.8/D-0.8 is the length scale to normalize x(cp), which is valid for subsonic, sonic, and supersonic twin-jets. As such, for a given p(e)/p(a) and M-j, the dependence of x(cp)/D on S/D can be predicted using the scaling law x(cp)/(S-1.8/D-0.8). Further, the scaling law is discussed, leading to an interpretation of the physical meaning of the dimensionless parameter (gamma M(j)(2)p(e)/p(a))(1/(jc+1)). Published under an exclusive license by AIP Publishing.