Effects Of Nozzle Lip Thickness Research Articles

Effect of velocity ratio and Mach number on thin lip coaxial jet

Abstract The effect of nozzle lip thickness and velocity ratio on coaxial subsonic jet mixing, at different Mach numbers, has been studied experimentally and numerically. Decay of coaxial subsonic jets emanating from coaxial nozzles of lip thickness 0.7, 1.7 and 2.65 mm with velocity ratio (VR) from 0.2 to 1.0 at primary jet exit Mach numbers of 0.6, 0.8 and 1.0 has been studied. Free jet without co-flow (VR0) was also studied for comparison. Jet centerline Mach number decay, turbulence and velocity variation in the radial direction are analyzed. The results show that mixing the coaxial jet at a low-velocity ratio is better than a high-velocity ratio, at all Mach numbers of the present study. The nozzle lip thickness has a significant influence on the secondary jet. Mixing of the jet in the presence of VR0.2 coaxial jet is found to be the highest. Characteristic decay of Mach 0.8 and 1.0 jet for lip thickness 1.7 and 2.65 mm is faster than lip thickness 0.7 mm. For a given lip thickness, increasing of velocity ratio is found to retard the mixing between primary and secondary jets.

Relationship between vortex and sound in under-expanded supersonic impinging jets

SUMMARY The study of an under-expanded supersonic jet impinging on a flat plate by using large-eddy simulation is reported. A third-order upwind compact difference and a fourth-order symmetric compact scheme are employed to discretize the nondimensional axisymmetric compressible Favre-filtered Navier–Stokes equations in space, whereas the third-order Runge–Kutta method with the total variation diminishing property is adopted to deal with the temporal discretization. The numerical simulation successfully captures the shock wave and vortex structures with different scales in the flow field. Waves with high and low frequencies traveling forward and reflecting back, and sound sources in different locations can be observed. By comparison with the frequency of the impinging tone from the experiment, it can be deduced that the change of pressure and swirling strength in the shear layer, pressure change on the impinging plate, and vortex merging in the jet shear layer are interdependent with the impinging tone. The effects of nozzle lip thickness on the impinging jet flow field have been investigated. The results show that the values of pressure fluctuation and vortex swirling strength in the shear layer near the nozzle have an extremum with the variation of the nozzle lip thickness. The results provide a theoretical foundation for the design of supersonic nozzles. Copyright © 2011 John Wiley & Sons, Ltd.

Acoustic properties associated with nozzle lip thickness in screeching jets

Imperfectly expanded supersonic jets generate discrete frequency sound known as screech tones. In the low supersonic Mach number, the screech phenomenon is axisymmetric. In this study the effect of nozzle lip thickness on the axisymmetric jet screech is investigated both by screech scattering computation and screeching jet simulation. The conservative form of the axisymmetric Euler equations in generalized coordinates are used to simulate a scattering problem and the Reynolds-Averaged Navier-Stokes equations with the modified Spalart-Allmaras turbulence model is employed for screeching jet simulation. Numerical results of scattered directivity pattern in scattering computation will be reported. Influence of the nozzle lip thickness on the momentum thickness, shock-cell spacing and screech tone wavelength is examined.

An experimental study of the nozzle lip thickness effect on supersonic jet screech tones

It is well known that screech tones of supersonic jet are generated by a feedback loop driven by the instability waves. Near the nozzle lip where the supersonic jet mixing layer is receptive to external excitation, acoustic disturbances impinging on this area excite the instability waves. This fact implies that the nozzle lip thickness can influence the screech tones of supersonic jet. The objective of the present study is to experimentally investigate the effect of nozzle-lip thickness on screech tones of supersonic jets issuing from a convergent-divergent nozzle. A baffle plate was installed at the nozzle exit to change the nozzle-lip thickness. Detailed acoustic measurement and flow visualization were made to specify the screech tones. The results obtained obviously show that nozzle-lip thickness significantly affects the screech tones of supersonic jet, strongly depending on whether the jet at the nozzle exit is over-expanded or under-expanded.

ラバルノズルからの超音速噴流騒音に及ぼすノズルリップ厚さの影響(S26-3 高速流れと衝撃波現象の基礎と応用その3,S26 高速流れと衝撃波現象の基礎と応用)

The effect of nozzle-lip thickness on supersonic jet noise generated from Laval nozzle with a design Mach number 2.0 was experimentally investigated using acoustic measurement and flow visualization. Experiments were carried out over a wide range of the nozzle pressure ratio from 2.0 to 18.0. The obtained results show that the nozzle-lip thickness significantly influences the acoustic characteristics of supersonic jet noise, such as jet oscillation mode, screech tone intensity and overall sound pressure level.

A241 超音速噴流騒音の特性に及ぼすノズルリップ厚さの影響

Under certain conditions, supersonic jet issuing from a supersonic nozzle invariably generates supersonic jet noise, which consists of three principal components ; the turbulent mixing noise, the broadband shock-associated noise, and the screech tones. In present study, it was experimentally investigated to the effect of nozzle lip thickness on the characteristics of supersonic jet noise. The convergent-divergent nozzle of design Mach number 2.0 was used in experiment. With two different cases in the nozzle-lip thickness, pressure ratio was varied in the range between 2.0 and 12.0. Acoustic measurements were conducted by microphones in an anechoic room, and the major structures of the supersonic jets were visualized by a Schlieren optical system for the purpose of the effect of nozzle lip thickness. The measured results show that the characteristics of supersonic jet noise, such as overall sound pressure level and screech frequency, depend upon the thickness of nozzle lip.

Effects of Jet Temperature and Nozzle-Lip Thickness on Screech Tones

Imperfectly expanded supersonic jets, invariably, generate discrete frequency sound known as screech tones. In the low supersonic jet Mach-number range of 1.0-1.25, the screech phenomenon is axisymmetric. In this investigation the effects of jet temperature and nozzle-lip thickness on the axisymmetric jet screech modes are studied by numerical simulation. At the present time there is no known way to predict the intensities of screech tones, even empirically, except by numerical simulation. Numerical results of screech frequencies and directivities of heated jets will be reported. The computed screech frequencies are found to agree well with experimental measurements. Computed tone intensities indicate a gradual decrease in the screech amplitude with an increase in jet temperature. Screech tones are known to be sensitive to the presence of acoustic reflection surfaces. Sound reflected off such surfaces could sometimes affect the feedback loop that drives the screech tones. The nozzle lip is a good reflection surface. As a part of this work, the effect of nozzle-lip thickness on screech tone frequency and intensity is investigated. There are good agreements between the computed tone frequencies, intensities, and experiments at several nozzle-lip thickness to jet diameter ratios. Thick lip nozzles, as expected, are found to generate the loudest tones. But the change in sound-pressure level between a thin and a thick lip nozzle is found to be quite modest.

The effects of nozzle exit lip thickness on plume resonance

The acoustic emission and initial shear layer of a cold jet issuing from an underexpanded sonic nozzle were measured where the lip thickness of the nozzle exit varied from 0·015 to 0·625 nozzle diameters. Because the amplitude of plume resonance (or screech) has been shown to be very sensitive to the initial conditions of the plume, the effects of nozzle lip thickness on this sound component in particular was investigated (although it will be shown that other noise components are also affected). Nearfield acoustic measurements have revealed the amplitude and frequency of certain modes of screech to be dependent on nozzle lip thickness. Fluctuating pressure measurements made on the nozzle exit surface have acoustic amplitudes in excess of near field microphone measurements. The dominant mode of instability that exists in the shear layer is also related to this geometric parameter. Detailed shear layer measurements were performed in an attempt to quantify any associated changes in the momentum thickness caused by altering the nozzle exit.