Acoustical modeling study of the open test section of the NASA Langley V/STOL wind tunnel

An acoustic model study was carried out to identify effective sound absorbing treatment of strategically located surfaces in an open wind tunnel test section. Also an aerodynamic study done concurrently, sought to find measures to control low frequency jet pulsations which occur when the tunnel is operated in its open test section configuration. The acoustical modeling study indicated that lining of the raised ceiling and the test section floor immediately below it, results in a substantial improvement. The aerodynamic model study indicated that: (1) the low frequency jet pulsations are most likely caused or maintained by coupling of aerodynamic and aeroacoustic phenomena in the closed tunnel circuit, (2) replacing the hard collector cowl with a geometrically identical but porous fiber metal surface of 100 mks rayls flow resistance does not result in any noticable reduction of the test section noise caused by the impingement of the turbulent flow on the cowl

Evaluation of the NASA Ames no. 1 7 by 10 foot wind tunnel as an acoustic test facility

Measurements were made in the no. 1 7'x10' wind tunnel at NASA Ames Research Center, with the objectives of defining the acoustic characteristics and recommending minimum cost treatments so that the tunnel can be converted into an acoustic research facility. The results indicate that the noise levels in the test section are due to (a) noise generation in the test section, associated with the presence of solid bodies such as the pitot tube, and (b) propagation of acoustic energy from the fan. A criterion for noise levels in the test section is recommended, based on low-noise microphone support systems. Noise control methods required to meet the criterion include removal of hardware items for the test section and diffuser, improved design of microphone supports, and installation of acoustic treatment in the settling chamber and diffuser

Studies of the near-field noise properties of a small air jet Final report

Turbulent eddy relationship to noise production in supersonic air je

A process-oriented language for describing aspects of reading comprehension

Includes bibliographical references (p. 36-38)The research described herein was supported in part by the National Institute of Education under Contract No. MS-NIE-C-400-76-011

Coherence and phase techniques applied to noise diagnosis in the NASA Ames 7 times 10-foot wind tunnel no. 1

Measurements have been made of coherence and phase spectra for the acoustic field in a subsonic wind tunnel. The data are interpreted in terms of simple analytical models for propagating and diffuse noise fields, including the presence of uncorrelated noise signals. It is found that low frequency noise propagates upstream and downstream from the fan, with the noise in the test section arriving in the upstream direction. High frequency sound is generated in the test section and propagates upstream and downstream. In the low frequency range, the ratio of diffuse to propagating energy is about eight for all locations in the test section, diffuser, and settling chamber; the value of the ratio increases with frequency

Feasibility of making sound power measurements in the NASA Langley V/STOL tunnel test section

Based on exploratory acoustic measurements in Langley's V/STOL wind tunnel, recommendations are made on the methodology for making sound power measurements of aircraft components in the closed tunnel test section. During airflow, tunnel self-noise and microphone flow-induced noise place restrictions on the amplitude and spectrum of the sound source to be measured. Models of aircraft components with high sound level sources, such as thrust engines and powered lift systems, seem likely candidates for acoustic testing

Acoustical Evaluation of the NASA Langley V/STOL Wind Tunnel

The results are presented of the acoustical measurements made to supply NASA Langley operating personnel with the acoustical characteristics of the tunnel test section needed for the planning of acoustical measurements and to identify the major noise sources. The results of the preliminary measurements of the spatial distribution of the sound field in the closed tunnel configuration indicate that the total sound power output of an unknown sound source placed in the test section could most probably be evaluated by measuring the sound pressure in two properly chosen locations in the duct - one upstream and one downstream of the test section. However, it is recommended that the practicability of this method of sound power output measurements be further investigated, preferably in a small scale model of the V/STOL Tunnel

On the design and test of a low noise propeller

An extensive review of noise and performance of general aviation propellers was performed. Research was done in three areas: The acoustic and aerodynamic theory of general aviation propellers, wind tunnel tests of three one-quarter scale models of general aviation propellers, and flight test of two low noise propellers. The design and testing of the second propeller is reviewed. The general aerodynamic considerations needed to design a new propeller are described. The design point analysis of low noise propellers is reviewed. The predicted and measured noise levels are compared

Measurement of model propulsion system noise in a low-speed wind tunnel

Methods are presented for making overall and directional acoustic measurements with forward velocity in the Lewis 9 x 15 V/STOL wind tunnel. Overall acoustic measurements are discussed; the acoustic calibration methods, instrumentation features, and types of experiments are presented. Selected data are presented as examples of the various types of overall measurements that are possible. The method of making directional acoustic measurements is presented, and the necessary alterations to the tunnel, specialized acoustic instrumentation, and calibration details are described. The results indicate that relative overall acoustic measurements can be made successfully and that directional acoustic measurements are feasible