scholarly journals Potential-core closing of temporally developing jets at Mach numbers between 0.3 and 2: Scaling and conditional averaging of flow and sound fields

2019 ◽  
Vol 4 (12) ◽  
Author(s):  
Christophe Bogey ◽  
Pierre Pineau
Keyword(s):  
Potential Core ◽  
Sound Fields ◽  
Mach Numbers ◽  
Conditional Averaging

scholarly journals BVI-noise generation by wing-shaped helicopter blade

2020 ◽  
Keyword(s):  
Calculated Data ◽  
Low Noise ◽  
Aerodynamic Noise ◽  
Noise Generation ◽  
High Frequency Region ◽  
Helicopter Blade ◽  
Sound Fields ◽  
Helicopter Flight ◽  
Natural Forms ◽  
Mach Numbers

Aerodynamic noise includes a number of noise components, among which rotational noise and vortex noise (BVI-noise) make the largest contribution to the overall noise generated. Rotation noise depends on the magnitude of the velocity of the incoming blade and prevails over other noise components at significant Mach Mach numbers. Unlike rotation noise, vortex noise is evident at low helicopter flight speeds, moderate Mach numbers. In the formation of this type of noise,an important role is played by the longitudinal geometry. Therefore, recently the shape of the helicopter blade is chosen close to existing natural forms, which are as balanced as possible. One of these may be a wing-shaped blade. In this work, the problem of generating BVI noise by the wing shaped blade of a helicopter is posed and solved. The mathematical model of the problem is constructed on the previously proposed by the author and successfully tested system of aeroacoustic equations for the general case. Estimated features in this system are pulsations of sound pressure and sound potential. The calculated data of these quantities, as well as their derivatives, were used to study near and far sound fields. In particular, the dependence of the density ripple distribution is revealed from the blade geometry, the angle of attack and the blade angle to the oncoming flow. Increasing flow velocity contributes to the emergence of transverse ripples on the surface blades that dominate the longitudinal ripples by level. An interesting feature noticed in the calculations is that there are calculations for moderate Mach numbers M=0.2,0.3 situations, at certain angles of blade placement to the stream and angles of attack where rotation noise dominates eddy noise. For values Mach numbers M>0.4 rotation noise plays a major role in blade noise generation. The noise level generated is in the range 50dB≤L≤60dB, which is lower by 5-6dB for the Blue Edge blade, as well as the rounded blade. In addition, activation of the high-frequency region in the frequency spectrum of noise was observed f≈840Hz. The results of the calculations show that the blade of the wing-shaped is low-noise in the mode of maneuvers at small flight speeds.

The vortex-street structure of turbulent jets. Part 2

1979 ◽  
Vol 368 (1735) ◽  
pp. 547-571 ◽  
Keyword(s):  
Full Range ◽  
Outer Part ◽  
Turbulent Jets ◽  
Companion Paper ◽  
Vortex Street ◽  
Potential Core ◽  
Jet Mixing ◽  
Mach Numbers ◽  
Jet Axis ◽  
Main Vortex

This paper is an extension of the work reported earlier as part 1 in a companion paper. It endeavours first to discover how the vortex-street structure in the round jet develops during its passage downstream, and secondly to resolve some of the questions concerning the flow structure in the outer part of the mixing region. It appears that the main vortex street that was reported in part 1 has a trajectory that converges on the jet axis at about two potential core lengths from the nozzle. This brings the vortex cores towards the axis and contributes to the erosion of the potential core. A branch vortex street apparently forms on the outer part of the jet mixing region downstream of x/D = 1.5, and as the main vortex street approaches the axis, the branch vortex street moves outwards. The vortices in the branch are jostled occasionally by those in the main vortex street, and various effects are caused, including the frequency modulation of the signals in the outer part of the mixing region. Measurements at higher Mach numbers confirm the appropriateness of Strouhal number scaling of the jet data for the full range of subsonic Mach numbers and suggest that the structure described in this paper is valid up to the sonic speed.

Measurements in subsonic and supersonic free jets using a laser velocimeter

1979 ◽  
Vol 93 (1) ◽  
pp. 1-27 ◽  
Author(s):  
Jark C. Lau ◽  
Philip J. Morris ◽  
Michael J. Fisher
Keyword(s):  
Mach Number ◽  
Error Function ◽  
Mixing Layer ◽  
Spreading Rate ◽  
Mean Velocity ◽  
Potential Core ◽  
Free Jets ◽  
Centre Line ◽  
Mach Numbers ◽  
Two Parameters

Velocity measurements in a 51 mm diameter turbulent jet are presented. The measurement programme is conducted in two parts. The first part is devoted to the validation of laser velocimeter (LV) data. This consists of comparative measurements with the LV and a hot-wire anemometer. The second part consists of a survey of the jet flow field at Mach 0·28, 0·90, and 1·37 under ambient temperature conditions. Radial and centre-line distributions of the axial and radial, mean and fluctuating velocities are obtained. The distributions indicate a decrease in the spreading rate of the mixing layer with increasing Mach number and a corresponding lengthening of the potential core. The results further indicate that these two parameters vary with the square of the jet Mach number. Radial distributions collapse when plotted in terms of ση*, where σ = 10.7/(1 - 0.273 MJ2) and η* = (r − r0·5)/x. This is true for distributions in planes located as far downstream as two potential core lengths. The collapsed data of mean velocity can be approximated by a Görtler error function profile: \[ U/U_J = 0.5[1-{\rm erf}(\sigma\eta^{*})]. \] Centre-line distributions at various Mach numbers also collapse if plotted in terms of x/xc, xc being the potential core length. A general equation for the collapsed data of mean velocity is given by: U/UJ = 1 - exp{1.35/(1 - x/xc)}, for the range of Mach numbers 0·3-1·4, where xc = 4.2 + 1.1 MJ2.

MULTIDIMENSIONAL SIMULATIONS AND TEST FIRES OF A HYDROGEN-FUELED RAMJET WITH AN ANNULAR DETONATIVE COMBUSTOR AT APPROACHING AIR FLOW OF MACH 2 AND 1.5

2020 ◽  
Author(s):  
V. S. IVANOV ◽  
◽  
V. S. AKSENOV ◽  
S. M. FROLOV ◽  
P. A. GUSEV ◽  
...  
Keyword(s):  
Unmanned Aerial Vehicles ◽  
High Speed ◽  
Constant Pressure ◽  
Air Flow ◽  
Thermodynamic Cycle ◽  
Aerial Vehicles ◽  
Mach Numbers

Modern high-speed unmanned aerial vehicles are powered with small-size turbojets or ramjets. Existing ramjets operating on the thermodynamic cycle with de§agrative combustion of fuel at constant pressure are efficient at flight Mach numbers M ranging from about 2 to 6.

Predictability of Deterministic Underwater Sound Fields

1993 ◽  
Author(s):  
Michael G. Brown ◽  
Frederick D. Tappert
Keyword(s):  
Underwater Sound ◽  
Sound Fields
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