Effects of Rectangular Nozzle Arrangement Interval on Characteristics of Multiple Rectangular Jets in a Line with Constant Aspect Ratio

Abstract

The mean velocity field of turbulent free jet issuing from multiple rectangular nozzles (Rectangular nozzle aspect ratio L/d=12.5) with semicircular shaped end, which are arranged parallel to each other in a line, has been investigated, experimentally and systematically. The aim of this study is to examine characteristics of the mean velocity field of multiple rectangular jets and to clarify an effect of rectangular nozzle arrangement interval S/d (=25.00, 18.75, 12.50 and 6.25) on characteristics of both velocity and length scales in the mean velocity field, then to furnish a data of multiple rectangular jets in a line for the engineering design. Measurements were made using an X-array Hot-Wire Probe (5.0μm in diameter, 1.0mm effective length) and linearized constant temperature anemometers. Signals from the anemometers were passed through low-pass filters and sampled using an A/D converter. The processing of the signals was done by a personal computer. The acquisition time of the signals was from 60 to 120 seconds. The Reynolds number based on the nozzle width d and the exit mean velocity Ue (@39 m/s) was kept constant at 25000, throughout this experiment. From this experiment, it was revealed that the potential core length of Uox/Ue on the x axis for all S/d cases existed until the section of x/d=7 which was the same with that of the single rectangular jet (Aspect Ratio: L/d=12.50) and the streamwise section indicating the two-dimensional jet decay (~(x/d)-0.5) moved toward the upstream region with the decreasing of S/d. The streamwise variation of the velocity scale Uox/Ue on the x axis showed the same decrease line with that of the two-dimensional jet from each downstream section, and also the length scale by/D2 on the long axis of rectangular nozzle indicated the same increase line with that of the two-dimensional jet from each downstream section, even if the rectangular nozzle arrangement interval S/d was different. Both of streamwise locations indicating the same decreasing characteristics of the velocity scale Uox/Ue on the x axis and the same increasing characteristics of the length scale by/d on the y axis with those of the two-dimensional jet, can be calculated approximately by two empirical formulas for any S/d case.