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Seiner, J. M.

Publications and source records attributed to Seiner, J. M..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
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

Proposed relationship between broadband shock associated noise and screech tones

It is recognized that the three principal components of the noise of shock containing supersonic jets, namely, the dominant part of turbulent mixing noise, the broadband shock associated noise and the screech tones are all generated directly by the large scale turbulence structures/instability waves of the jet flow. In this paper the relationship between broadband shock associated noise and screech tones is examined. It is shown that from the spectral characteristics point of view, the screech tones may be regarded as special cases of broadband shock associated noise. Theoretical calculations for the peak frequencies of broadband shock associated noise and the fundamental frequencies of screech tones are carried out. These calculations are free from empirical constants. The calculated results are found to agree favorably with experimental measurements.

Tam, C. K. W.↗
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

Analysis of turbulent underexpanded jets. II - Shock noise features using SCIPVIS

SCIPVIS, the computational model discussed by Dash et al. (1985), is assessed in predicting the complicated flow structure associated with shock-containing plumes. In addition, the analysis in this study examines this code's applicability as a basic part of a program for estimating broadband shock noise radiation. The results of this study show that excellent agreement exists between predicted and measured static pressure distributions for both underexpanded and overexpanded flow cases considered. Of the three turbulence closure models incorporated in the SCIPVIS code, the kW model of Spalding produces the most uniform agreement with measurement. The k-epsilon-2 model of Launder consistently overestimates plume spreading for supersonic jets with exit Mach numbers in the 1-2 range. Dash's (1983) k-epsilon-2-cc, compressibility-corrected version of Launder's model underestimates plume spreading. Good qualitative agreement was also obtained between the measured longitudinal turbulence intensity and that predicted by the code for the same trial case. Comparison of measured and predicted broadband shock noise spectrum peak values were found to be in excellent agreement. This utilized a variant of the Harper-Bourne and Fisher (1973) phase-array model: the effective shock spacing was reinterpreted as the value of the end of the plume potential core, determined herein by the SCIPVIS code.

Seiner, J. M.↗
NASA NTRS1985

Analysis of turbulent underexpanded jets. I - Parabolized Navier-Stokes model, SCIPVIS

A new computational model (SCIPVIS) is described which predicts the multiple-cell wave/shock structure in underexpanded or overexpanded turbulent jets. SCIPVIS solves the parabolized Navier-Stokes jet-mixing equations utilizing a shock-capturing approach in supersonic regions of the jet and a pressure-split approach in subsonic regions. Turbulence processes are represented by the solution of compressibility-corrected two-equation turbulence models. SCIPVIS presently analyzes jets exhausting into a quiescent or supersonic external stream for which a single-pass spatial-marching solution can be obtained. The features of SCIPVIS are reviewed, and calculations are described exhibiting the influence of turbulence modelling, jet temperature, and flight velocity on the jet shock structure.

Dash, S. M.↗
NASA NTRS1985

A multiple-scales model of the shock-cell structure of imperfectly expanded supersonic jets

The present investigation is concerned with the development of an analytical model of the quasi-periodic shock-cell structure of an imperfectly expanded supersonic jet. The investigation represents a part of a program to develop a mathematical theory of broadband shock-associated noise of supersonic jets. Tam and Tanna (1982) have suggested that this type of noise is generated by the weak interaction between the quasi-periodic shock cells and the downstream-propagating large turbulence structures in the mixing layer of the jet. In the model developed in this paper, the effect of turbulence in the mixing layer of the jet is simulated by the addition of turbulent eddy-viscosity terms to the momentum equation. Attention is given to the mean-flow profile and the numerical solution, and a comparison of the numerical results with experimental data.

Tam, C. K. W.↗
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.↗
NASA NTRS1984

On the relationship between broadband shock associated noise and screech tones

It is recognized that the three principal components of the noise of shock containing supersonic jets, namely, the dominant part of turbulent mixing noise, the broadband shock associated noise and the screech tones are all generated directly by the large scale turbulence structures/instability waves of the jet flow. In this paper the relationship between broadband shock associated noise and screech tones is examined. It is shown that from the spectral characteristics point of view, the screech tones may be regarded as special cases of broadband shock associated noise. Theoretical calculations for the peak frequencies of broadband shock associated noise and the fundamental frequencies of stable screech tones are carried out. The calculated results are found to agree favorably with experimental measurements.

Tam, C. K. W.↗
NASA NTRS1984

Advances in high speed jet aeroacoustics

This paper provides an assessment from an experimental point of view of the present understanding of high speed jet noise primarily as it pertains to shock containing supersonic jet plumes. The nature of this assessment involves an examination of the complex flow and related acoustic field associated with this problem. A certain emphasis is placed on prediction of the near acoustic field to satisfy a motivation driven by a new set of guiding principles, namely the high performance tactical fighter and second generation space transportation vehicles. The review concludes that after weighing all the experimental evidence, only after consideration of the role of large scale coherent structure is adopted can a consistent unifying theme be achieved to physically interpret and properly predict noise generation by the fundamental mechanisms.

Seiner, J. M.↗
NASA NTRS1983

The wedge hot-film anemometer in supersonic flow

A commercial wedge hot-film probe is studied to determine its heat transfer response in transonic to low supersonic flows of high unit Reynolds number. The results of this study show that its response in this flow regime differs from the response of cylindrical type sensors. Whereas the cylindrical sensor has the same sensitivity to velocity as to density for free-stream Mach numbers exceeding 1.3, the wedge probe sensitivity to velocity is always greater than its sensitivity to density over the entire flow regime. This property requires determination of three fluctuation components due to density, velocity, and temperature, in a transonic or supersonic turbulent flow. Sensitivity equations are derived based on the observed behavior of the wedge probe. Both the durability and the frequency response of the probe are excellent, the square wave insertion test indicating frequency response near 130 kHz. The directional response of the probe at sonic speed is poor and requires further examination before Reynolds stress measurements are attempted with dual sensor probes.

Seiner, J. M.↗
NASA NTRS1983

Nearfield observations of tones generated from supersonic jet flows

The physics of discrete tone generation (screech) from improperly expanded supersonic jets have been investigated experimentally. Both nearfield acoustic survey and phase-averaged schlieren flow visualization were conducted. The dominant mode of flow oscillation that occurred during intense screech and its coupling with the internal shock structure and external sound field were established. Deductions made from the observed coupling mechanism revealed the importance of Helmholtz number and shock cell spacing in the maintenance of screech. Measured amplitude variation of screech are compared with computed amplitude variation of the dominant instability. The results suggest that jet instability plays a direct role in the generation of screech.

Yu, J. C.↗
NASA NTRS1983

Shock noise features using the SCIPVIS code

The numerical computational supersonic jet plume model SCIPVIS was analyzed in order to determine its effectiveness for predicting the complicated flow structure associated with supersonic shock containing jet plumes. The analysis focused on assessing the applicability of using this code for predicting the broadband shock noise radiation. The analysis was carried out for several exit Mach number cases (including 1.00, 1.41, and 1.99) covering both underexpanded and overexpanded flow conditions. The three primary turbulence closure models incorporated in the SCIPVIS code were utilized for comparisons to measured plume static pressure distributions. Among other results, the prediction of plume static pressures for all three nozzle exit Mach numbers was found to perform exceptionally well when compared with experimental data for both underexpanded and overexpanded cases. Computations performed using this code for calculating the average shock wavelength for the 1.99 exit Mach number case were shown to provide an excellent prediction of the peak frequency for broadband shock noise. The spatial variation of the turbulent kinetic energy was found to be in qualitative agreement with wedge hot-film measurements.

Seiner, J. M.↗
NASA NTRS1982

Measurements of Mean Static Pressure and Far Field Acoustics of Shock Containing Supersonic Jets

The far field acoustic data base generated in studies of broadband shock noise from supersonic jets is presented. Both conical and contoured nozzles of exit Mach numbers 1.0, 1.5, and 2.0 were tested using unheated air at pressure ratios ranging from 1.9 to 14. Tests were performed both with and without screech suppression tabs. Overall sound pressure variations and representative 1/3-octave and narrowband spectra are presented. The mean static pressure measured within these jets is also surveyed.

Norum, T. D.↗
NASA NTRS1982

Supersonic jet noise generated by large scale instabilities

The role of large scale wavelike structures as the major mechanism for supersonic jet noise emission is examined. With the use of aerodynamic and acoustic data for low Reynolds number, supersonic jets at and below 70 thousand comparisons are made with flow fluctuation and acoustic measurements in high Reynolds number, supersonic jets. These comparisons show that a similar physical mechanism governs the generation of sound emitted in he principal noise direction. These experimental data are further compared with a linear instability theory whose prediction for the axial location of peak wave amplitude agrees satisfactorily with measured phased averaged flow fluctuation data in the low Reynolds number jets. The agreement between theory and experiment in the high Reynolds number flow differs as to the axial location for peak flow fluctuations and predicts an apparent origin for sound emission far upstream of the measured acoustic data.

Seiner, J. M.↗
NASA NTRS1981

Acoustic near field and local flow properties associated with broadband shock noise

Shock noise associated with unheated supersonic jets were investigated using a near field microphone array and a single sensor wedge shaped hot-film probe. Both over and underexpanded cases were investigated using Mach 1.5 and 2.0 convergent-divergent nozzles. Correlation measurements through each shock cell of a single underexpanded case with the Mach 1.5 nozzle were obtained between the hot-film probe and microphone array. The results show for the Mach number cases selected that the probe's response is primarily sensitive to velocity. The results of the hot-film near field microphone correlations show general agreement with certain theoretical models as to the location for shock noise production, although they demonstrate the existence of some large perhaps turbulent structure that collectively interacts and phases the motion of the downstream shocks. The near field microphone correlations demonstrate that downstream shocks dominate shock noise production, and suggests the existence of a Doppler effect in near field of the sources. In addition broadband shock noise is found to also propagate at small angles to the jet axis.

Seiner, J. M.↗