Effect of Nozzle Inflow Conditions on Shock-Cell Structure and Noise in Overexpanded Jets

2019 ◽  
Author(s):  
Junhui Liu ◽  
Andrew T. Corrigan ◽  
Ryan F. Johnson ◽  
Ravi Ramamurti
Keyword(s):  
Cell Structure ◽  
Shock Cell ◽  
Inflow Conditions

Studies on high speed jets from nozzles with internal grooves

2004 ◽  
Vol 108 (1079) ◽  
pp. 43-50 ◽  
Author(s):  
S. Elangovan ◽  
E. Rathakrishnan
Keyword(s):  
High Speed ◽  
Cell Structure ◽  
Pressure Profile ◽  
Equivalent Diameter ◽  
Streamwise Vortices ◽  
Shock Cell ◽  
Underexpanded Jets ◽  
Pitot Pressure ◽  
Mean Pressure ◽  
The Mean

Experiments were carried out on jets issuing from circular nozzles with grooved exits and the results compared with those of the plain nozzle. The plain nozzle had an exit diameter of 10mm. Because of the introduction of semi-circular grooves at the exit, the effective or equivalent diameter of the grooved nozzles was 10·44mm. The groove lengths were varied as 3, 5 and 8mm. The nozzles were operated at fully expanded sonic and underexpanded exit conditions. The corresponding fully expanded Mach numbers were 1·0 and 1·41. The shock cell structure of the underexpanded jets from grooved nozzles appeared to be weaker than that of the plain nozzle, as indicated by lesser amplitudes of the cyclic variation of the Pitot pressure. The iso-Mach contours indicate that the jet spread along the grooved plane is significantly higher than that along the ungrooved plane. Off-centre peaks were observed in the mean pressure profile of underexpanded jets from grooved nozzles. They were probably due to the streamwise vortices shed from the grooves.

Schlieren 3D-CT Measuremsnt of Instantaneous Density Distributions of the Shock-cell Structure of Under-Expanded Supersonic Jets

2016 ◽  
Vol 2016 (0) ◽  
pp. J0510203
Author(s):  
Ahmad Z. NAZARI ◽  
Naoki HAYASHI ◽  
Yuta ISHIKO ◽  
Kimihiro NAGASE ◽  
Kazuma KAKIMOTO ◽  
...  
Keyword(s):  
Cell Structure ◽  
Supersonic Jets ◽  
3D Ct ◽  
Shock Cell ◽  
Density Distributions

Sound generated by instability wave/shock-cell interaction in supersonic jets

2007 ◽  
Vol 587 ◽  
pp. 173-215 ◽  
Author(s):  
PRASUN K. RAY ◽  
SANJIVA K. LELE
Keyword(s):  
Cell Structure ◽  
Cell Interaction ◽  
Linear Instability ◽  
Supersonic Jets ◽  
Instability Wave ◽  
Destructive Interference ◽  
Source Terms ◽  
Mean Flow ◽  
Shock Cell ◽  
Instability Waves

Broadband shock-associated noise is an important component of the overall noise generated by modern airplanes. In this study, sound generated by the weakly nonlinear interaction between linear instability waves and the shock-cell structure in supersonic jets is investigated numerically in order to gain insight into the broadband shock-noise problem. The model formulation decomposes the overall flow into a mean flow, linear instability waves, the shock-cell structure and shock-noise. The mean flow is obtained by solving RANSequations with a k-ε model. Locally parallel stability equations are solved for the shock structure, and linear parabolized stability equations are solved for the instability waves. Then, source terms representing the instability wave/shock-cell interaction are assembled and the inhomogeneous linearized Euler equations are solved for the shock-noise.Three cases are considered, a cold under-expanded Mj = 1.22 jet, a hot under-expanded Mj = 1.22 jet, and a cold over-expanded Mj = 1.36 jet.Shock-noise computations are used to identify and understand significant trends in peak sound amplitudes and radiation angles. The peak sound radiation angles are explained well with the Mach wave model of Tam & Tanna J. Sound Vib. Vol. 81, 1982, p. 337). The observed reduction of peak sound amplitudes with frequency correlates well with the corresponding reduction of instability wave growth with frequency. However, in order to account for variation of sound amplitude for different azimuthal modes, the radial structure of the instability waves must be considered in additionto streamwise growth. The effect of heating on the Mj = 1.22 jet is shown to enhance the sound radiated due to the axisymmetric instability waves while the other modesare relatively unaffected. Solutions to a Lilley–Goldstein equation show that soundgenerated by ‘thermodynamic’ source terms is small relative to sound from ‘momentum’ sources though heating does increase the relative importance of the thermodynamic source. Furthermore, heating preferentially amplifies sound associated with the axisymmetric modes owing to constructive interference between sound from the momentumand thermodynamic sources. However, higher modes show destructive interference between these two sources and are relatively unaffected by heating.

scholarly journals Absolute instability in shock-containing jets

2021 ◽  
Vol 930 ◽  
Author(s):  
Petrônio A.S. Nogueira ◽  
Peter Jordan ◽  
Vincent Jaunet ◽  
André V.G. Cavalieri ◽  
Aaron Towne ◽  
...  
Keyword(s):  
Cell Structure ◽  
Saddle Points ◽  
Flow Analysis ◽  
Mode Shapes ◽  
Absolute Instability ◽  
Mean Flow ◽  
Shock Cell ◽  
Spatially Periodic ◽  
Spatio Temporal ◽  
Parallel Case

We present an analysis of the linear stability characteristics of shock-containing jets. The flow is linearised around a spatially periodic mean, which acts as a surrogate for a mean flow with a shock-cell structure, leading to a set of partial differential equations with periodic coefficients in space. Disturbances are written using the Floquet ansatz and Fourier modes in the streamwise direction, leading to an eigenvalue problem for the Floquet exponent. The characteristics of the solution are directly compared with the locally parallel case, and some of the features are similar. The inclusion of periodicity induces minor changes in the growth rate and phase velocity of the relevant modes for small shock amplitudes. On the other hand, the eigenfunctions are now subject to modulation related to the periodicity of the flow. Analysis of the spatio-temporal growth rates led to the identification of a saddle point between the Kelvin–Helmholtz mode and the guided jet mode, characterising an absolute instability mechanism. Frequencies and mode shapes related to the saddle points for two conditions (associated with axisymmetric and helical modes) are compared with screech frequencies and the most energetic coherent structures of screeching jets, resulting in a good agreement for both. The analysis shows that a periodic shock-cell structure has an impulse response that grows upstream, leading to oscillator behaviour. The results suggest that screech can occur in the absence of a nozzle, and that the upstream reflection condition is not essential for screech frequency selection. Connections to previous models are also discussed.

scholarly journals Assessment of Short Rectangular-Tab Actuation of Supersonic Jet Mixing

Actuators ◽  
2020 ◽  
Vol 9 (3) ◽  
pp. 72 ◽  
Author(s):  
Abhash Ranjan ◽  
Mrinal Kaushik ◽  
Dipankar Deb ◽  
Vlad Muresan ◽  
Mihaela Unguresan
Keyword(s):  
Coming Out ◽  
Nozzle Exit ◽  
Stokes Equations ◽  
Cell Structure ◽  
Pressure Ratio ◽  
Supersonic Jet ◽  
Three Dimensional ◽  
Shock Cell ◽  
Jet Mixing ◽  
Nozzle Pressure

This work explores the extent of jet mixing for a supersonic jet coming out of a Mach 1.8 convergent-divergent nozzle, controlled with two short rectangular vortex-generating actuators located diametrically opposite to each other with an emphasis on numerical methodology. The blockage ratio offered by the tabs is around 0.05. The numerical investigations were carried out by using a commercial computational fluid dynamics (CFD) package and all the simulations were performed by employing steady Reynolds-averaged Navier–Stokes equations and shear-stress transport k−ω turbulence model on a three-dimensional computational space for more accuracy. The numerical calculations are administered at nozzle pressure ratios (NPRs) of 4, 5, 6, 7 and 8, covering the overexpanded, the correctly expanded and the underexpanded conditions. The centerline pressure decay and the pressure profiles are plotted for both uncontrolled and the controlled jets. Numerical schlieren images are used to capture the barrel shock, the expansion fans and the Mach waves present in the flow field. Mach contours are also delineated at varying NPRs indicating the number of shock cells, their length and the variation of the shock cell structure and strength, to substantiate the prominent findings. The outcomes of this research are observed to be in sensible concurrence with the demonstrated exploratory findings. A reduction in the jet core length of 75% is attained with small vortex-generating actuators, compared to an uncontrolled jet, corresponding to nozzle pressure ratio 5. It was also seen that the controlled jet gets bifurcated downstream of the nozzle exit at a distance of about 5 D, where D is the nozzle exit diameter. Furthermore, it was fascinating to observe that the jet spread increases downstream of the nozzle exit for the controlled jet, as compared to the uncontrolled jet at any given NPR.

scholarly journals Screech tones from rectangular jets with spanwise oblique shock-cell structures

1997 ◽  
Vol 330 ◽  
pp. 141-168 ◽  
Author(s):  
GANESH RAMAN
Keyword(s):  
Aspect Ratio ◽  
Fatigue Failure ◽  
Cell Structure ◽  
Oblique Shock ◽  
Spanwise Direction ◽  
Shock Cell ◽  
Cell Spacing ◽  
Cell Structures ◽  
Shaped Nozzle ◽  
Amplitude Mode

Understanding screech is especially important for the design of advanced aircraft because screech can cause sonic fatigue failure of aircraft structures. Although the connection between shock-cell spacing and screech frequency is well understood, the relation between non-uniformities in the shock-cell structures and the resulting amplitude, mode, and steadiness of screech have remained unexplored. This paper addresses the above issues by intentionally producing spanwise (larger nozzle dimension) variations in the shock-cell structures and studying the resulting spanwise screech mode. The spanwise-oblique shock-cell structures were produced using imperfectly expanded convergent–divergent rectangular nozzles (aspect ratio = 5) with non-uniform exit geometries. Three geometries were studied: (a) a nozzle with a spanwise uniform edge, (b) a nozzle with a spanwise oblique (single-bevelled) edge, and (c) a nozzle that had two spanwise oblique (double-bevelled) cuts to form an arrowhead-shaped nozzle. For all nozzles considered, the screech mode was antisymmetric in the transverse (smaller nozzle dimension) direction allowing focus on changes in the spanwise direction. Three types of spanwise modes were observed: symmetric (I), antisymmetric (II), and oblique (III). The following significant results emerged: (i) for all cases the screech mode corresponds with the spanwise shock-cell structure, (ii) when multiple screech modes are present, the technique presented here makes it possible to distinguish between coexisting and mutually exclusive modes, (iii) the strength of shocks 3 and 4 influences the screech source amplitude and determines whether screech is unsteady. The results presented here offer hope for a better understanding of screech and for tailoring shock-containing jets to minimize fatigue failure of aircraft components.

Computation of Shock Cell Structure of Dual-Stream Jets for Noise Prediction

AIAA Journal ◽  
2008 ◽  
Vol 46 (11) ◽  
pp. 2857-2867 ◽  
Author(s):  
Christopher K. W. Tam ◽  
Nikolai N. Pastouchenko ◽  
K. Viswanathan
Keyword(s):  
Cell Structure ◽  
Noise Prediction ◽  
Shock Cell
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