STUDIES ON TWIN NONPARALLEL UNVENTILATED HIGH-SPEED JETS

The interaction of twin high-speed jets is an important problem which is most relevant to aircraft engine exhaust systems. Many studies have been carried out on twin parallel high-speed jets, but similar studie s for non-parallel configurations are almost absent. Such an investiga tion would be useful in understanding jet flow fields associated with V/STOL aircraft. The present work is an attempt to investigate experim entally the interaction of two high-speed axisymmetric jets obliquely oriented towards each other. Twin nozzles of exit diameter (D) 10mm ar e set on a common end wall with their axes intersecting each other at half-angles (a) of 0, 5, 10 and 15 degrees. The centre-to-centre spaci ngs (S) of the nozzles, non-dimensionalized as SID, are varied as 3.1, 4 and 5. The nozzles are operated at fully expanded sonic and underex panded exit conditions to yield fully expanded Mach numbers M-j of 1, 1.19, 1.41 and 1.52. Some of the conclusions arrived at were based on the experimental results and are given below In the case of sonic jets , the variation of mean velocity along the nozzle block centre-line ca n be correlated with empirical equations based on the geometric inters ection distance and the maximum centreline velocity. In general, at a particular nozzle spacing and angle of interception, the merging dista nce decreases with increasing fully expanded Mach numbers. In most of the cases, the complete combining of the twin jets into a single jet o ccurs downstream of the geometric intersection point, the location of the combining point being strongly influenced by the fully expanded Ma ch number.