Masters Theses

Date of Award

12-1998

Degree Type

Thesis

Degree Name

Master of Science

Major

Aerospace Engineering

Major Professor

Carroll E. Peters

Committee Members

Ahmad Vakili, Ching Lo

Abstract

Mach number uniformity in a 16-foot-square supersonic wind tunnel (Tunnel 16S) at the Arnold Engineering Development Center's Propulsion Wind Tunnel Facility was evaluated. Tunnel 16S is a continuous-flow, closed-circuit tunnel with a 101-foot-long, flexible-wall, Laval nozzle that can provide test-section Mach numbers from 1.50 to 4.75. It has been hypothesized that the observed Mach number nonuniformity is, at least partially, a result of two discontinuous regions in the nozzle contours. These discontinuous regions are a result of the nozzle-plate "lap joints", vertical seams in the nozzle walls. A 2-D, time-dependent, inviscid Euler code, NAP, was used to compute Mach number profiles along the length of the supersonic portion of the nozzle. Nozzle contours evaluated included the design nozzle contours, measured nozzle contours, calibrated nozzle contours, and smoothed nozzle contours for Mach numbers of 1.60 and 2.50. The design nozzle contours were determined by calculating a floating cubic fit through the design nozzle contour specifications. The measured nozzle contours were obtained from measurements taken along the entire length of the supersonic portion of both the East and West walls using a state-of-the-art laser tracking system, the SMX Tracker 4000. The differences between the design and measured nozzle contours result from four contributing factors: 1) the nozzle-positioning-jack errors, 2) the lap joints, 3) miscellaneous manufacturing errors, and 4) the inability to accurately position the nozzle wall with a finite number of jacks. The calibrated nozzle contours were free of nozzle-positioning-jack errors, and the smoothed nozzle contours were free of both nozzle-positioning-jack errors and lap-joint irregularities. The results infer that the nozzle-positioning-jack errors are a significant contributor to the Mach number nonuniformity in the test section. The lap joints are also a significant contributor at Mach 1.60. In addition, the smoothed nozzle contours resulted in Mach nonuniformities of more than twice the future goal of ± 0.004. This leads to the conclusion that the design nozzle contour specifications may need to be modified or the future goal relaxed.

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