Experimental and computational investigation of double serpentine nozzle

Infrared radiation signatures of gas turbine engine exhaust are suppressed markedly when equipped with a serpentine nozzle compared to an axisymmetric nozzle. The aim of this paper is to research more detailed flow characteristics of the serpentine nozzle, and to this end a double serpentine nozzle cold fluid test was conducted in this paper, static pressures on the nozzle walls surface were measured, and schlieren flow visualizations downstream of the nozzle exit were observed. Then numerical simulations of the experimental model were carried out using CFD software with k-ε turbulence model adopted. And the effects of geometric design parameters (the length ratio of first S length to second S length and the centerline distributions) on serpentine nozzle performance were investigated numerically. Detailed flow characteristics were presented including the distributions of static pressure, Ma number (streamlines), wall shear stress (limited streamlines), and the total pressure. Results show good agreement between the experimental data and computation. Static pressure distributions on the upper and down walls surface of double serpentine nozzle are completely different compared to the traditional axisymmetric nozzle. The rapid turning and steep passage slope of the serpentine nozzle would result in high friction loss and strong secondary flow loss, hence the value of the length ratio of first S passage to second S passage is recommended to be chosen from 2:5 to 2:3. The centerline distributions are crucial to the nozzle design for its influence on air acceleration inside the nozzle. The centerlines with a rapid turning at the exit would result in a high Ma number, which brings on high friction loss and secondary loss at the turnings. For maximum efficiency of centerline distributions, it is recommended that curves with a gentle turning at each serpentine passage exit should be chosen.