Sound and turbulence modulation by particles in high-speed shear flows

2019 ◽  
Vol 875 ◽  
pp. 254-285 ◽  
Author(s):  
David A. Buchta ◽  
Gregory Shallcross ◽  
Jesse Capecelatro
Keyword(s):  
Gas Phase ◽  
High Speed ◽  
Pressure Fluctuations ◽  
Sound Radiation ◽  
Rate Of Change ◽  
Intensity Increase ◽  
Mass Loading ◽  
Local Pressure ◽  
Time Rate ◽  
Particle Laden Flows

High-speed free-shear-flow turbulence, laden with droplets or particles, can radiate weaker pressure fluctuations than its unladen counterpart. In this study, Eulerian–Lagrangian simulations of high-speed temporally evolving shear layers laden with monodisperse, adiabatic, inertial particles are used to examine particle–turbulence interactions and their effect on radiated pressure fluctuations. An evolution equation for gas-phase pressure intensity is formulated for particle-laden flows, and local mechanisms of pressure changes are quantified over a range of Mach numbers and particle mass loadings. Particle–turbulence interactions alter the local pressure intensity directly via volume displacement (due to the flow of finite-size particles) and drag coupling (due to local slip velocity between phases), and indirectly through significant turbulence changes. The sound radiation intensity near subsonic mixing layers increases with mass loading, consistent with existing low Mach number theory. For supersonic flows, sound levels decrease with mass loading, consistent with trends observed in previous experiments. Particle-laden cases exhibit reduced turbulent kinetic energy compared to single-phase flow, providing one source of their sound changes; however, the subsonic flow does not support such an obvious source-to-sound decomposition to explain its sound intensity increase. Despite its decrease in turbulence intensity, the louder particle-laden subsonic flows show an increase in the magnitude and time-rate-of-change of fluid dilatation, providing a mechanism for its increased sound radiation. Contrasting this, the quieter supersonic particle-laden flows exhibit decreased gas-phase dilatation yet its time-rate-of-change is relatively insensitive to mass loading, supporting such a connection.

A Theory for the Vibratory Effects Produced by a Propeller on a Large Plate

1959 ◽  
Vol 3 (04) ◽  
pp. 1-10
Author(s):  
John P. Breslin
Keyword(s):  
High Speed ◽  
Infinite Plate ◽  
Rate Of Change ◽  
Infinite Plane ◽  
Time Rate ◽  
Transverse Axis ◽  
Elastic Wall ◽  
The Moment ◽  
Ship Propeller ◽  
Speed Computer

The flow generated on an infinite plane or wall by a single-bladed ship propeller rotating on a shaft parallel to the plane in a uniform superposed stream is first considered. After demonstrating that the pressure on the wall depends only on blade position and not upon the time-rate-of-change of blade position, the force and the moment on the plane about a transverse axis are computed and found to be given by very simple formulas. Under the assumed neglect of the interferences arising from the image of the propeller in the wall, it is shown that the net force and moment on the wall are zero for all lightly loaded propellers having two or more blades. The case of nonuniform inflow is considered and shown to give nonzero vibratory forces. The case of uniform inflow is still of interest because the zero force and moment result does not mean that an elastic wall would not vibrate, and to substantiate this, a formula for the deflections of a thin "infinite" plate is given. This formula has not been evaluated because of its complexity. It is recommended that numerical evaluation be undertaken through the use of a high-speed computer.

Experimental Investigation of Cavity Patterns and Noise Characteristics

2016 ◽  
Author(s):  
Byoung-Kwon Ahn ◽  
So-won Jeong ◽  
Ji-Hye Kim
Keyword(s):  
High Speed ◽  
Pressure Fluctuations ◽  
Low Noise ◽  
Growth Patterns ◽  
Marine Propeller ◽  
Underwater Noise ◽  
Local Pressure ◽  
Noise Characteristics ◽  
Measured Pressure ◽  
Pressure Cavity

When a marine propeller with the wing shape rotates at high speed underwater, local pressure on the blade decreases and various types of cavitation inevitably occur in where the local pressure falls below the vapor pressure. Cavity reduces the efficiency, erodes the propeller surface, and generate vibration and serious noise. Especially, underwater noise caused by cavitation is directly connected to the comfort of commercial ships and also the survivability of naval vessels. In order to reduce the occurrence of the cavitation and to design low noise propeller, it is demanded to figure out the correlation of noise characteristics with growth patterns of the cavity. In this paper, we observed global behavior of partial cavities generated on two-dimensional hydrofoils and made a map of cavity patterns. We also measured pressure fluctuations and investigated noise characteristics directly connected with the process of occurrence of the cavity.

Composite cladded powders for spraying of protective coatings

2019 ◽  
pp. 59-64
Author(s):  
E. Yu. Gerashchenkova ◽  
T. I. Bobkova ◽  
E. A. Samodelkin ◽  
B. V. Farmakovsky
Keyword(s):  
Tungsten Carbide ◽  
Gas Phase ◽  
High Speed ◽  
Protective Coatings ◽  
Powder Materials ◽  
Nanosized Particles

The paper presents results of the development of technology for producing cladded and surfacealloyed powder materials. High-speed mechanosynthesis of matrix powders of FeCrAl and solid nanosized particles of tungsten carbide occurs in a disintegrator in the presence of an active gas phase (nitrogen).

Relationship Between Unsteady Flow, Pressure Fluctuations, and Noise in a Centrifugal Pump—Part B: Effects of Blade-Tongue Interactions

1995 ◽  
Vol 117 (1) ◽  
pp. 30-35 ◽  
Author(s):  
S. Chu ◽  
R. Dong ◽  
J. Katz
Keyword(s):  
Unsteady Flow ◽  
Centrifugal Pump ◽  
Pressure Difference ◽  
Pressure Fluctuations ◽  
Primary Sources ◽  
Pressure Measurements ◽  
Local Pressure ◽  
Pressure Distributions ◽  
Flow Pressure ◽  
Tip Of The Tongue

Maps of pressure distributions computed using PDV data, combined with noise and local pressure measurements, are used for identifying primary sources of noise in a centrifugal pump. In the vicinity of the impeller pressure minima occur around the blade and near a vortex train generated as a result of non-uniform outflux from the impeller. The pressure everywhere also varies depending on the orientation of the impeller relative to the tongue. Noise peaks are generated when the pressure difference across the tongue is maximum, probably due to tongue oscillations, and when the wake impinges on the tip of the tongue.

A Brief Review of Wind Effects on Buildings and Structures

1966 ◽  
Vol 70 (665) ◽  
pp. 553-560 ◽  
Author(s):  
C. Scruton
Keyword(s):  
Air Flow ◽  
Pressure Fluctuations ◽  
Ground Level ◽  
Vertical Gradient ◽  
Proximity Effects ◽  
Wind Tunnels ◽  
Wind Loading ◽  
Local Pressure ◽  
Wind Speeds ◽  
Random Forcing

SummaryPresent day structural forms and methods of fabrication have considerably increased the importance of wind as a design consideration. For estimations of the overall stability of a structure and of the local pressure distribution on the cladding, a knowledge of the maximum steady or time-averaged wind loads is usually sufficient. Mind tunnel tests to determine the wind loading coefficients are often made in smooth uniform flow, but for more accurate data account must be taken of the effects of the vertical gradient of wind speed and the turbulence of natural winds. Further research is needed into these effects and also into methods of obtaining a sufficient representation of the natural wind in the wind tunnel.There are a number of ways by which wind excites structures into oscillation; among these are vortex excitation, galloping, proximity effects including buffeting, stalling flutter and classical flutter. The vortex and galloping excitation might be expected to be especially sensitive to the turbulence properties of the air flow. Also, in the absence of any mechanism for instability, atmospheric turbulence may directly excite oscillations through the random forcing by the pressure fluctuations which it produces. Further understanding of this problem must come through research into the effects of turbulence (and to the extent to which these effects may be disregarded), but the range of the conditions is so vast and complicated that it seems unlikely that sufficient aerodynamic and wind data will be accumulated to permit the response of a proposed structure to be calculated with reasonable certainty, and for major projects it is anticipated that comprehensive tests on aeroelastic models in wind tunnels with appropriate turbulent air flow will continue to offer the more reliable predictions.The air flow around buildings is of concern inasmuch as it influences the dispersal of combustion and other gases from the smokestack and also in its effect on the speeds and turbulence of the wind over areas used by pedestrians. The erection of a tall building may cause an increase in wind speeds and gustiness at ground level. These problems of the external flow over buildings are readily examined in wind tunnels. For this purpose tunnels with large working sections are desirable to permit a sufficiently wide area of the neighbourhood to be represented.

scholarly journals Strong Azimuthal Combustion Instabilities in a Spray Annular Chamber With Intermittent Partial Blow-Off

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Kevin Prieur ◽  
Daniel Durox ◽  
Thierry Schuller ◽  
Sébastien Candel
Keyword(s):  
Light Intensity ◽  
High Speed ◽  
Transverse Velocity ◽  
Pressure Fluctuations ◽  
Pressure Sensors ◽  
Nodal Line ◽  
Operating Conditions ◽  
Acoustic Energy ◽  
Transverse Motion ◽  
Azimuthal Mode

This article reports experiments carried out in the MICCA-spray combustor developed at EM2C laboratory. This system comprises 16 swirl spray injectors. Liquid n-heptane is injected by simplex atomizers. The combustion chamber is formed by two cylindrical quartz tubes allowing full optical access to the flame region and it is equipped with 12 pressure sensors recording signals in the plenum and chamber. A high-speed camera provides images of the flames and photomultipliers record the light intensity from different flames. For certain operating conditions, the system exhibits well defined instabilities coupled by the first azimuthal mode of the chamber at a frequency of 750 Hz. These instabilities occur in the form of bursts. Examination of the pressure and the light intensity signals gives access to the acoustic energy source term. Analysis of the phase fluctuations between the two signals is carried out using cross-spectral analysis. At limit cycle, large pressure fluctuations of 5000 Pa are reached, and these levels persist over a finite period of time. Analysis of the signals using the spin ratio indicates that the standing mode is predominant. Flame dynamics at the pressure antinodal line reveals a strong longitudinal pulsation with heat release rate oscillations in phase and increasing linearly with the acoustic pressure for every oscillation levels. At the pressure nodal line, the flames are subjected to large transverse velocity fluctuations leading to a transverse motion of the flames and partial blow-off. Scenarios and modeling elements are developed to interpret these features.

scholarly journals Mixing and chemical reactions in a turbulent liquid mixing layer

1986 ◽  
Vol 170 ◽  
pp. 83-112 ◽  
Author(s):  
M. M. Koochesfahani ◽  
P. E. Dimotakis
Keyword(s):  
Reynolds Number ◽  
Gas Phase ◽  
Turbulent Mixing ◽  
High Speed ◽  
High Reynolds Number ◽  
Schmidt Number ◽  
Mixing Layer ◽  
Entrainment Ratio ◽  
High Reynolds ◽  
Mixed Fluid

An experimental investigation of entrainment and mixing in reacting and non-reacting turbulent mixing layers at large Schmidt number is presented. In non-reacting cases, a passive scalar is used to measure the probability density function (p.d.f.) of the composition field. Chemically reacting experiments employ a diffusion-limited acid–base reaction to directly measure the extent of molecular mixing. The measurements make use of laser-induced fluorescence diagnostics and high-speed, real-time digital image-acquisition techniques.Our results show that the vortical structures in the mixing layer initially roll-up with a large excess of fluid from the high-speed stream entrapped in the cores. During the mixing transition, not only does the amount of mixed fluid increase, but its composition also changes. It is found that the range of compositions of the mixed fluid, above the mixing transition and also throughout the transition region, is essentially uniform across the entire transverse extent of the layer. Our measurements indicate that the probability of finding unmixed fluid in the centre of the layer, above the mixing transition, can be as high as 0.45. In addition, the mean concentration of mixed fluid across the layer is found to be approximately constant at a value corresponding to the entrainment ratio. Comparisons with gas-phase data show that the normalized amount of chemical product formed in the liquid layer, at high Reynolds number, is 50% less than the corresponding quantity measured in the gas-phase case. We therefore conclude that Schmidt number plays a role in turbulent mixing of high-Reynolds-number flows.

GT36 Turbine Aero-Thermal Development and Validation

2017 ◽  
Author(s):  
S. Naik ◽  
J. Krueckels ◽  
M. Henze ◽  
W. Hofmann ◽  
M. Schnieder
Keyword(s):  
Gas Turbine ◽  
High Speed ◽  
Pressure Sensors ◽  
Thermal Design ◽  
Local Pressure ◽  
Cooling Systems ◽  
Wide Range ◽  
Turbine Vanes ◽  
Thermal Development ◽  
Development And Validation

This paper describes the aero-thermal development and validation of the GT36 heavy duty gas turbine. The turbine which has evolved from the existing and proven GT26 design, consists of an optimised annulus flow path, higher lift aerofoil profiles, optimised aerodynamic matching between the turbine stages and new and improved cooling systems of the turbine vanes and blades. A major design feature of the turbine has been to control and reduce the aerodynamic losses, associated with the aerofoil profiles, trailing edges, blade tips, endwalls and coolant ejection. The advantages of these design changes to the overall gas turbine efficiency have been verified via extensive experimental testing in high-speed cascade test rigs and via the utilisation of high fidelity multi-row computational fluid dynamics design systems. The thermal design and cooling systems of the turbine vanes, blades have also been improved and optimised. For the first stage vane and blade aerofoils and platforms, multi-row film cooling with new and optimised diffuser cooling holes have been implemented and validated in high speed linear cascades. Additionally, the internal cooling design features of all the blades and vanes were also improved and optimised, which allowed for more homogenous metal temperatures distributions on the aerofoils. The verification and validation of the internal thermal designs of all the turbine components has been confirmed via extensive testing in dedicated Perspex models, where measurements were conducted for local pressure losses, overall flow distributions and local heat transfer coefficients. The turbine is currently being tested and undergoing validation in the GT36 Test Power Plant in Birr, Switzerland. The gas turbine is heavily instrumented with a wide range of validation instrumentation including thermocouples, pressure sensors, strain gauges and five-hole probes. In addition to performance mapping and operational validation, a dedicated thermal paint validation test will also be performed.

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