On cumulative nonlinear acoustic waveform distortions from high-speed jets

2014 ◽  
Vol 749 ◽  
pp. 331-366 ◽  
Author(s):  
W. J. Baars ◽  
C. E. Tinney ◽  
M. S. Wochner ◽  
M. F. Hamilton
Keyword(s):  
Mach Number ◽  
Acoustic Waves ◽  
High Speed ◽  
Scaling Laws ◽  
Nonlinear Distortion ◽  
Practical Interest ◽  
Laboratory Scale ◽  
Potential Core ◽  
Nonlinear Distortions ◽  
Gaussian Source

AbstractA model is proposed for predicting the presence of cumulative nonlinear distortions in the acoustic waveforms produced by high-speed jet flows. The model relies on the conventional definition of the acoustic shock formation distance and employs an effective Gol’dberg number$\Lambda $for diverging acoustic waves. The latter properly accounts for spherical spreading, whereas the classical Gol’dberg number$\Gamma $is restricted to plane wave applications. Scaling laws are then derived to account for the effects imposed by jet exit conditions of practical interest and includes Mach number, temperature ratio, Strouhal number and an absolute observer distance relative to a broadband Gaussian source. Surveys of the acoustic pressure produced by a laboratory-scale, shock-free and unheated Mach 3 jet are used to support findings of the model. Acoustic waveforms are acquired on a two-dimensional grid extending out to 145 nozzle diameters from the jet exit plane. Various statistical metrics are employed to examine the degree of local and cumulative nonlinearity in the measured waveforms and their temporal derivatives. This includes a wave steepening factor (WSF), skewness, kurtosis and the normalized quadrature spectral density. The analysed data are shown to collapse reasonably well along rays emanating from the post-potential-core region of the jet. An application of the generalized Burgers equation is used to demonstrate the effect of cumulative nonlinear distortion on an arbitrary acoustic waveform produced by a high-convective-Mach-number supersonic jet. It is advocated that cumulative nonlinear distortion effects during far-field sound propagation are too subtle in this range-restricted environment and over the region covered, which may be true for other laboratory-scale jet noise facilities.

Experimental investigation on mixing characteristics of high speed co-flow jets by using tabbed chevron nozzle

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Saravanan A. R. ◽  
Thanigaiarasu S. ◽  
Rakesh Divvela ◽  
Rathakrishnan E.
Keyword(s):  
Experimental Investigation ◽  
Mach Number ◽  
High Speed ◽  
Radial Profile ◽  
Mixing Enhancement ◽  
Primary Flow ◽  
Potential Core ◽  
Mixing Characteristics ◽  
Chevron Nozzle ◽  
Better Than

Abstract The present study investigates the effect of chevron with tab (Tabbed chevron) fixed at the exit of the co-flowing primary nozzle on the mixing characteristics in subsonic and sonic jets. The experiment was conducted for the jet Mach number 0.6 and 0.8. The centerline Mach number decay was calculated for all these jet Mach numbers for the co-flow baseline nozzle, nozzle with chevrons and tabbed chevron (primary flow) nozzle respectively. It was found that tabbed chevron was effective in reducing the potential core length by 88.23% as compared to the chevron nozzle with baseline nozzle. The radial profile also shows that the mixing enhancement by tabbed chevron is better than chevron nozzle.

scholarly journals High-speed turbulent gas jets: an LES investigation of Mach and Reynolds number effects on the velocity decay and spreading rate

2021 ◽  
Author(s):  
Francesco Bonelli ◽  
Annarita Viggiano ◽  
Vinicio Magi
Keyword(s):  
Mach Number ◽  
High Speed ◽  
Stokes Equations ◽  
Fluid Dynamic ◽  
Spreading Rate ◽  
Navier Stokes ◽  
Potential Core ◽  
Jet Mixing ◽  
Gas Jets ◽  
Velocity Decay

AbstractThe aim of this work is the investigation of Mach and Reynolds numbers effects on the behaviour of turbulent gas jets in order to gain new insights into the fluid dynamic process of turbulent jet mixing and spreading. An in-house solver (Flow-Large Eddy and Direct Simulation, FLEDS) of the Favre-filtered Navier Stokes equations has been used. Compressibility has been analyzed by considering gas jets with Mach number equal to 0.8, 1.4, 2.0 and 2.6, and Re equal to 10,000. As concerns the influence of Re on gas jets, four cases have been investigated, i.e. $$\mathrm{Re} = 2500$$ Re = 2500 , 5000, 10,000 and 20,000, with Mach number equal to 1.4. The results show that, in accordance with previous experimental and numerical studies, the potential core length increases with Mach number. As regards the velocity decay and the spreading rate downstream of the potential core, compressibility effects are not relevant except for the jet with Mach number of 2.6. The normalized turbulent kinetic energy along the centerline as a function of the normalized streamwise distance shows a similar peak at the end of the potential core for all jets, except for the case with Mach number of 2.6. By increasing Re, the length of the potential core decreases up to the same value for all Re higher than 10,000. In the region downstream of the potential core, the velocity decay decreases as Re number increases from 10,000 to 20,000, whereas, for lower values of Re, the influence is almost negligible.

scholarly journals On noise generation in low Reynolds number temporal round jets at a Mach number of 0.9

2018 ◽  
Vol 859 ◽  
pp. 1022-1056 ◽  
Author(s):  
Christophe Bogey
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Acoustic Waves ◽  
Mixing Layer ◽  
Noise Generation ◽  
Noise Component ◽  
Potential Core ◽  
Lower Velocity ◽  
Round Jets ◽  
Jet Axis

Two temporally developing isothermal round jets at a Mach number of 0.9 and Reynolds numbers of 3125 and 12 500 are simulated in order to investigate noise generation in high-subsonic jet flows. Snapshots and statistical properties of the flow and sound fields, including mean, root-mean-square and skewness values, spectra and auto- and cross-correlations of velocity and pressure, are presented. The jet at a Reynolds number of 12 500 develops more rapidly, exhibits more fine turbulent scales and generates more high-frequency acoustic waves than the other. In both cases, however, when the jet potential core closes, mixing-layer turbulent structures intermittently intrude on the jet axis and strong low-frequency acoustic waves are emitted in the downstream direction. These waves are dominated by the axisymmetric mode and are significantly correlated with centreline flow fluctuations. These results are similar to those obtained at the end of the potential core of spatially developing jets. They suggest that the mechanism responsible for the downstream noise component of these jets also occurs in temporal jets, regardless of the Reynolds number. This mechanism is revealed by averaging the flow and pressure fields of the present jets using a sample synchronization with the minimum values of centreline velocity at potential-core closing. A spot characterized by a lower velocity and a higher level of vorticity relative to the background flow field is found to develop in the interfacial region between the mixing layer and the potential core, to strengthen rapidly and reach a peak intensity when arriving on the jet axis, and then to break down. This is accompanied by the growth and decay of a hydrodynamic pressure wave, propagating at a velocity which, initially, is close to 65 per cent of the jet velocity and slightly increases, but quickly decreases after the collapse of the high-vorticity spot in the flow. During that process, sound waves are radiated in the downstream direction.

Experimental investigation on mixing characteristics of high speed co-flow jets by using tabbed chevron nozzle

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Saravanan A. R. ◽  
Thanigaiarasu S. ◽  
Rakesh Divvela ◽  
Rathakrishnan E.
Keyword(s):  
Experimental Investigation ◽  
Mach Number ◽  
High Speed ◽  
Radial Profile ◽  
Mixing Enhancement ◽  
Primary Flow ◽  
Potential Core ◽  
Mixing Characteristics ◽  
Chevron Nozzle ◽  
Better Than

Abstract The present study investigates the effect of chevron with tab (Tabbed chevron) fixed at the exit of the co-flowing primary nozzle on the mixing characteristics in subsonic and sonic jets. The experiment was conducted for the jet Mach number 0.6 and 0.8. The centerline Mach number decay was calculated for all these jet Mach numbers for the co-flow baseline nozzle, nozzle with chevrons and tabbed chevron (primary flow) nozzle respectively. It was found that tabbed chevron was effective in reducing the potential core length by 88.23% as compared to the chevron nozzle with baseline nozzle. The radial profile also shows that the mixing enhancement by tabbed chevron is better than chevron nozzle.

scholarly journals Aerodynamic Losses in Turbines with and without Film Cooling, as Influenced by Mainstream Turbulence, Surface Roughness, Airfoil Shape, and Mach Number

2012 ◽  
Vol 2012 ◽  
pp. 1-28 ◽  
Author(s):  
Phil Ligrani
Keyword(s):  
Surface Roughness ◽  
Mach Number ◽  
Film Cooling ◽  
Total Pressure ◽  
High Speed ◽  
Density Ratio ◽  
Aerodynamic Loss ◽  
Pressure Losses ◽  
Loss Coefficients ◽  
Exit Mach Number

The influences of a variety of different physical phenomena are described as they affect the aerodynamic performance of turbine airfoils in compressible, high-speed flows with either subsonic or transonic Mach number distributions. The presented experimental and numerically predicted results are from a series of investigations which have taken place over the past 32 years. Considered are (i) symmetric airfoils with no film cooling, (ii) symmetric airfoils with film cooling, (iii) cambered vanes with no film cooling, and (iv) cambered vanes with film cooling. When no film cooling is employed on the symmetric airfoils and cambered vanes, experimentally measured and numerically predicted variations of freestream turbulence intensity, surface roughness, exit Mach number, and airfoil camber are considered as they influence local and integrated total pressure losses, deficits of local kinetic energy, Mach number deficits, area-averaged loss coefficients, mass-averaged total pressure loss coefficients, omega loss coefficients, second law loss parameters, and distributions of integrated aerodynamic loss. Similar quantities are measured, and similar parameters are considered when film-cooling is employed on airfoil suction surfaces, along with film cooling density ratio, blowing ratio, Mach number ratio, hole orientation, hole shape, and number of rows of holes.

Auto and Cross Correlation Measurements in a Turbine Cascade Using a Digital Correlator

1982 ◽  
Author(s):  
P. J. Bryanston-Cross ◽  
J. J. Camus
Keyword(s):  
Mach Number ◽  
High Speed ◽  
Cross Correlation ◽  
Turbine Blades ◽  
Image Plane ◽  
Strongly Correlated ◽  
Trailing Edge ◽  
Number Range ◽  
Cross Correlations ◽  
Digital Correlator

A simple technique has been developed which samples the dynamic image plane information of a schlieren system using a digital correlator. Measurements have been made in the passages and in the wakes of transonic turbine blades in a linear cascade. The wind tunnel runs continuously and has independently variable Reynolds and Mach number. As expected, strongly correlated vortices were found in the wake and trailing edge region at 50 KHz. Although these are strongly coherent we show that there is only limited cross-correlation from wake to wake over a Mach no. range M = 0.5 to 1.25 and variation of Reynolds number from 3 × 105 to 106. The trailing edge fluctuation cross correlations were extended both upstream and downstream and preliminary measurements indicate that this technique can be used to obtain information on wake velocity. The vortex frequency has also been measured over the same Mach number range for two different cascades. The results have been compared with high speed schlieren photographs.

Splash formation by spherical drops

2001 ◽  
Vol 427 ◽  
pp. 73-105 ◽  
Author(s):  
LIOW JONG LENG
Keyword(s):  
High Resolution ◽  
Quantitative Data ◽  
Water Surface ◽  
High Speed ◽  
Scaling Laws ◽  
Capillary Wave ◽  
Water Drop ◽  
Qualitative And Quantitative ◽  
High Resolution Images ◽  
The Impact

The impact of a spherical water drop onto a water surface has been studied experimentally with the aid of a 35 mm drum camera giving high-resolution images that provided qualitative and quantitative data on the phenomena. Scaling laws for the time to reach maximum cavity sizes have been derived and provide a good fit to the experimental results. Transitions between the regimes for coalescence-only, the formation of a high-speed jet and bubble entrapment have been delineated. The high-speed jet was found to occur without bubble entrapment. This was caused by the rapid retraction of the trough formed by a capillary wave converging to the centre of the cavity base. The converging capillary wave has a profile similar to a Crapper wave. A plot showing the different regimes of cavity and impact drop behaviour in the Weber–Froude number-plane has been constructed for Fr and We less than 1000.

Standing acoustic waves in a low Mach number shear flow

AIAA Journal ◽  
1992 ◽  
Vol 30 (7) ◽  
pp. 1708-1715 ◽  
Author(s):  
Meng Wang ◽  
David R. Kassoy
Keyword(s):  
Mach Number ◽  
Shear Flow ◽  
Acoustic Waves ◽  
Low Mach Number

Large-scale structure and entrainment in the supersonic mixing layer

1995 ◽  
Vol 284 ◽  
pp. 171-216 ◽  
Author(s):  
N. T. Clemens ◽  
M. G. Mungal
Keyword(s):  
Mach Number ◽  
High Speed ◽  
Large Scale ◽  
Mixture Fraction ◽  
Mixing Layer ◽  
Mie Scattering ◽  
Planar Laser ◽  
The Cross ◽  
Convective Mach Number ◽  
Stream Direction

Experiments were conducted in a two-stream planar mixing layer at convective Mach numbers,Mc, of 0.28, 0.42, 0.50, 0.62 and 0.79. Planar laser Mie scattering (PLMS) from a condensed alcohol fog and planar laser-induced fluorescence (PLIF) of nitric oxide were used for flow visualization in the side, plan and end views. The PLIF signals were also used to characterize the turbulent mixture fraction fluctuations.Visualizations using PLMS indicate a transition in the turbulent structure from quasi-two-dimensionality at low convective Mach number, to more random three-dimensionality for$M_c\geqslant 0.62$. A transition is also observed in the core and braid regions of the spanwise rollers as the convective Mach number increases from 0.28 to 0.62. A change in the entrainment mechanism with increasing compressibility is also indicated by signal intensity profiles and perspective views of the PLMS and PLIF images. These show that atMc= 0.28 the instantaneous mixture fraction field typically exhibits a gradient in the streamwise direction, but is more uniform in the cross-stream direction. AtMc= 0.62 and 0.79, however, the mixture fraction field is more streamwise uniform and with a gradient in the cross-stream direction. This change in the composition of the structures is indicative of different entrainment motions at the different compressibility conditions. The statistical results are consistent with the qualitative observations and suggest that compressibility acts to reduce the magnitude of the mixture fraction fluctuations, particularly on the high-speed edge of the layer.

Experimental Investigation of Turbine Stage Flow Field and Performance at Varying Cavity Purge Rates and Operating Speeds

2016 ◽  
Author(s):  
Johan Dahlqvist ◽  
Jens Fridh
Keyword(s):  
Mach Number ◽  
Flow Field ◽  
High Speed ◽  
Control Volume ◽  
Spatial Average ◽  
Turbine Stage ◽  
Wide Range ◽  
Annulus Flow ◽  
Purge Flow ◽  
Secondary Air

The aspect of hub cavity purge has been investigated in a high-pressure axial low-reaction turbine stage. The cavity purge is an important part of the secondary air system, used to isolate the hot main annulus flow from cavities below the hub level. A full-scale cold-flow experimental rig featuring a rotating stage was used in the investigation, quantifying main annulus flow field impact with respect to purge flow rate as it was injected upstream of the rotor. Five operating speeds were investigated of which three with respect to purge flow, namely a high loading case, the peak efficiency, and a high speed case. At each of these operating speeds, the amount of purge flow was varied across a very wide range of ejection rates. Observing the effect of the purge rate on measurement plane averaged parameters, a minor outlet swirl decrease is seen with increasing purge flow for each of the operating speeds while the Mach number is constant. The prominent effect due to purge is seen in the efficiency, showing a similar linear sensitivity to purge for the investigated speeds. An attempt is made to predict the efficiency loss with control volume analysis and entropy production. While spatial average values of swirl and Mach number are essentially unaffected by purge injection, important spanwise variations are observed and highlighted. The secondary flow structure is strengthened in the hub region, leading to a generally increased over-turning and lowered flow velocity. Meanwhile, the added volume flow through the rotor leads to higher outlet flow velocities visible in the tip region, and an associated decreased turning. A radial efficiency distribution is utilized, showing increased impact with increasing rotor speed.

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