An Experimental Study on Performance of Second Throat Exhaust Diffusers of Different Configuration

Abstract

Second throat supersonic exhaust diffusers (STEDs) were designed to simulate high-altitude conditions according to the normal-shock model. Experimental studies were performed on the STEDs to investigate how performance characteristics varied with the length and diameter of the STED using high-pressure nitrogen gas. The variation in performance due to length indicated that the performance of the STED could be very slightly improved by adjusting the diffuser inlet length ( ), and it could be significantly improved by optimizing the second throat length ratio (   ) and the divergence length ( ). The starting and vacuum chamber pressures exhibited the highest level of performance near     of the design point.

Numerical Study on the Flow and Heat Transfer Characteristics of a Second Throat Exhaust Diffuser According to Variations in Operating Pressure and Geometric Shape

“…In the present study, the STED used for high-altitude simulation was designed through use of the one-dimensional normal shock theory based on various technical and design data [18]. This STED system was comprised of a vacuum chamber, a diffuser entrance (L d ), a converging section (L c ), a second throat (L st ), and a diverging section (L s ), as shown in Figure 1.…”

“…Therefore, the computational grids of the present study were set to y + ≤ 1 near the wall to fit the SST k-ω turbulence model, and the total number of grids was approximately 120,000, based on the subscale diffuser. In order to increase the accuracy of the calculation results, a mesh sensitivity study was performed according to the procedures of previous studies [18]. We performed experiments using a 1/5.6 subscale diffuser operating at a pressure of 50 bar using cold-flow nitrogen.…”

“…In this study, we investigated the effect of diffuser entrance length L d (where the supersonic flow is expanded when starting the diffuser), the length ratio of the second throat L st /D st (where the transition from supersonic to subsonic flow occurs), and the length of the diverging section L s (where temperature and pressure recovery occurs), as depicted in Figure 1. The dimensions of the baseline diffuser were as follows: L d = 100 mm, L st /D st = 8, and L s = 644 mm [18]. Based on these dimensions, investigations were performed under various geometric configurations.…”