Engineering topics

Ponton, M. K.

Publications and source records attributed to Ponton, M. K..

8 records

NASA NTRS1999

Effect of Swirl on Noise from a High Aspect Ratio Rectangular Nozzle

Based on extensive work performed by Dr. Thomas H. Sobota (Advanced Projects Research Incorporated (APRI)) on swirling flows in circular-to-rectangular transition sections, a model assembly was designed and fabricated in support of a Phase 1 Small Business Innovation Research Contract between the NASA-Langley Research Center and APRI. This assembly was acoustically tested as part of this Phase 1 effort, the goal being to determine whether the controlled introduction of axial vorticity could affect the various noise generation mechanisms present in an underexpanded supersonic rectangular jet.

Ponton, M. K.↗

NASA NTRS1993

Mach wave emission from a high temperature supersonic jet

The paper considers the compressible Rayleigh equation as a model for the Mach wave emission mechanism associated with high temperature supersonic jets. Solutions to the compressible Rayleigh equation reveal the existence of several families of supersonically convecting instability waves. These waves directly radiate noise to the jet far field. The predicted noise characteristics are compared to previously acquired experimental data for an axisymmetric Mach 2 fully pressure balanced jet operating over a range of jet operating total temperatures from ambient to 1370 K. The results of this comparison show that the first order supersonic instability wave and the Kelvin-Helmholtz first, second, and third order modes have directional radiation characteristics that are in agreement with observed data. The assumption of equal initial amplitudes for all of the waves leads to the conclusion that the flapping mode of instability dominates the noise radiation process of supersonic jets. At a jet temperature of 1370 K, supersonic instability waves are predicted to dominate the noise radiated at high frequency at narrow angles to the jet axis.

Seiner, J. M.↗

NASA NTRS1992

The effects of nozzle exit lip thickness on plume resonance

The acoustic emission and initial shear layer of a cold jet issuing from an underexpanded sonic nozzle were measured where the lip thickness of the nozzle exit varied from 0.015 to 0.625 nozzle diameters. Because the amplitude of plume resonance (or screech) has been shown to be very sensitive to the initial conditions of the plume, the effects of nozzle lip thickness on this sound component in particular was investigated (although it will be shown that other noise components are also affected). Nearfield acoustic measurements have revealed the amplitude and frequency of certain modes of screech to be dependent on nozzle lip thickness. Fluctuating pressure measurements made on the nozzle exit surface have acoustic amplitudes in excess of near field microphone measurements. The dominant mode of instability that exists in the shear layer is also related to this geometric parameter. Detailed shear layer measurements were performed in an attempt to quantify any associated changes in the momentum thickness caused by altering the nozzle exit.

Ponton, M. K.↗

NASA NTRS1986

Far-field acoustics of supersonic rectangular nozzles with various throat aspect ratios

The far-field acoustic behavior of supersonic jets produced by four rectangular nozzles with various throat aspect ratios are reported. One nozzle tested was designed for an exit Mach number of 1.66 with throat aspect ratio of 2.0. The remaining three nozzles (throat aspect ratios of 3.7, 5.8, 7.6) were designed for an exit Mach number of 1.35. Acoustic results presented include narrowband spectra and overall sound pressures for numerous operating pressure ratios and spatial locations.

Ponton, M. K.↗

NASA NTRS1986

The preferred spatial mode of instability for a Mach 2 jet

Phase-averaged schlieren video and an array of azimuthally oriented microphones were used in the experiments performed to determine the preferred spatial structure associated with supersonic nozzle design for an exhaust Mach number of 2. The jet flow was unheated, chemically inert, and submerged in a static environment, conditions that are satisfactory for the quasi-linear wave-analytical model of Tam and Morris (1980) and Tam and Burton (1984). For general conditions of undeterminate phase-averaged optical records, a conditional sampling method was devised, based on fundamental multimode components. This method uncovers the preferred spatial structure, and shows that in addition to the dominant jet flapping mode, there is also a significant contribution from the axisymmetric mode. Near-field correlations with a moving microphone indicate that the flapping plane is nearly stationary, and not spinning as in the Westley and Wolley (1975) experiment.

Seiner, J. M.↗

NASA NTRS1986

Acoustic properties associated with rectangular geometry supersonic nozzles

Acoustic property experiments have been conducted to ascertain the behavior of rectangular geometry supersonic nozzles whose throat aspect ratios vary over a 2.0-7.6 range, and whose three partial sidewall geometries range from full to 75-percent cutback. The tests employed unheated air at static conditions for nozzle Mach numbers of 1.35-1.66. It is found that sonic fatigue failures are possible at certain partial sidewall geometries and high nozzle aspect ratios. Unlike axisymmetric supersonic nozzles, shock noise dominates both the rear and forward arc for throat aspect ratio cases greater than 5.6. Jet screech frequency was adequately predicted with a simple vortex sheel model.

Seiner, J. M.↗

NASA NTRS1986

Dynamic pressure loads associated with twin supersonic plume resonance

The phenomenon of twin supersonic plume resonance is defined and studied as it pertains to high level dynamic loads in the inter-nozzle region of aircraft like the F-15 and B1-A. Using a 1/40th scale model twin jet nacelle with powered choked nozzles, it is found that intense internozzle dynamic pressures are associated with the synchrophased coupling of each plume's jet flapping mode. This condition is found most prevalent when each plume's jet flapping mode has constituent elements composed of the B-type helical instability. Suppression of these fatigue bearing loads was accomplished by simple geometric modifications to only one plume's nozzle. These modifications disrupt the natural selection of the B-type mode and thereby decouple the plumes.

Seiner, J. M.↗

NASA NTRS1985

Aeroacoustic data for high Reynolds number supersonic axisymmetric jets

Both aerodynamic and near field acoustic behavior of several unheated axisymmetric shock free and shock containing high speed jet plumes are reported. The exit Mach number range for these data is from 0.9 to 2.5. The aerodynamic measurements include both mean and turbulence quantities for a shock free jet plume produced by a convergent divergent nozzle designed to have an exit Mach number of 2. The near field acoustic measurements presented include narrow band spectra, directivity and contour plots of select one third octave band data, and near field microphone correlations from a linear array. Shock noise results are also included as obtained by operating an underexpanded convergent nozzle at the design point of two supersonic exist Mach number convergent divergent nozzles.

Seiner, J. M.↗