Increase Of Jet Temperature Research Articles

Effect of Relative Jet Temperature in Supersonic Dual-Impinging Jets

Short takeoff and vertical landing aircraft configurations involve multiple jets that impinge onto the deck surface in tandem and lead to several adverse effects. This study reports on the experimental characterization of supersonic dual-impinging jets by systematically varying their relative jet temperature. A sonic converging and Mach 1.5 converging–diverging (CD) nozzles are employed. The expansion ratio of the converging nozzle is maintained at 0.96, 1.19, and 1.59, and the CD nozzle is operated at a fixed nozzle pressure ratio of 3. The temperature ratio of the jet from the CD nozzle is varied from 1.0, 1.3, and 1.7. For a fixed momentum of the jet pair, an increase in jet temperature intensified the nearfield noise and unsteadiness on the impingement surface. At short impingement heights, resonance in the heated jet was the primary source of unsteadiness. At a fixed impingement height, an increase in jet temperature led to a systematic increase in tonal frequency, while jet instability mode shapes were retained. Furthermore, the mean flowfield of sonic jet and fountain regions remain unaffected, and an increase in supersonic jet velocity is observed. This is also accompanied by an increase in unsteadiness in the fountain upwash.

Experimental investigation on the erosion behaviors of frozen-thawed sandstone under abrasive supercritical CO2 jet impingement

An abrasive supercritical CO2 jet (ASJ) was used to erode sandstone subjected to freeze-thaw cycles and the erosion performance was investigated through laboratory experiments. The erosion characteristics of frozen-thawed and unfrozen sandstones under ASJ impingement at various jet temperature, jet pressure, and standoff distance were compared. It was found that the jet operating parameters shows very different effects on the two types of sandstones because of the fundamental differences in microstructure and mechanical properties. Frozen-thawed sandstones are more susceptible to erosion by ASJ impact due to the deterioration of rock physical properties under the periodic freeze-thaw cycles. Conical erosion craters are formed in unfrozen sandstones at all tested standoff distances, while at small standoff distances a regular deep hole is generated in the center of frozen-thawed sandstone with large pieces of rock peeled off around the hole due to jet pressurization. For both types of sandstones, the erosion depth decreases with the increase of jet temperature as the particle impact velocity decreases under the reduced drag force, and the decrease of kinetic energy and number of abrasives near the jet periphery at higher jet temperature results in smaller erosion area. There is a positive correlation between the size of erosion crater and the jet pressure, and the growth rate of frozen-thawed sandstone is much higher. SEM inspections reveal that frozen-thawed specimens show messy eroded surfaces with more diversified microstructural features. Sandstones are eroded predominantly by intergranular fracture, but the proportion of transgranular fracture increases with the increase of freeze-thaw cycle number.

Inflow characteristics for generating axis-switching phenomenon of heated rectangular jets

Flow characteristics due to the axis-switching phenomenon are numerically investigated for heated rectangular jets with typical inlet conditions and three aspect ratios (AR), namely 1.0, 1.5, and 2.0. To examine various inlets and their relation to the axis-switching flow, an inflow generator is newly devised, wherein jet flows from an orifice plate and a long pipe nozzle can be realized. Depending on the inlet conditions, the 45° and 90° axis-switching phenomena for the rectangular jet are observed to appear differently. As the aspect ratio increases and jet temperature decreases, the axis-switching positions are delayed downstream. It is observed that the strong and weak states of the axis-switching flows can be interpreted by the crossover locations of the jet half-widths and the saddle-shaped velocity profile is not the only main factor for axis-switching flow. As the jet temperature increases, a well-mixed state is quickly obtained, and the mixing performance of the square jet is better than that of the rectangular jet. For both isothermal and heated jets, the flow mixing is improved by the axis-switching flow. Various analyses are attempted to find the specific inlet structure for the axis-switching flow. From the results, the special features for inflow criterion producing axis-switching flow can be explained by factors such as the deformation parameter, interrelations between shear strain and normal rates, turbulence-driven and geometry-driven streamwise vortices, and normal Reynolds stresses.

Steady active control of noise radiation from highly heated supersonic jets.

The goal of the present investigation is to study the effect of using fluid inserts for noise control at high exhaust temperatures by performing a sequence of large eddy simulations on a typical military-style nozzle, both with and without fluid inserts, at jet inlet total temperature ratios of 2.5, 5, and 7. An exact physics-based splitting of the jet flow-field into its hydrodynamic, acoustic, and thermal components reveals clear evidence of a reduction in the radiation efficiency of Mach waves from the controlled jet. This effect is far more pronounced at afterburner conditions, where the location of the maximum noise reduction is observed to shift upstream with increase in jet temperature, thus matching the maximum location of the jet OASPL directivity. Moreover, the maximum noise reduction achieved at afterburner conditions exceeds that obtained at lower exhaust temperatures. This is encouraging and shows that the effectiveness of the fluid inserts improves with an increase in jet exhaust temperature. Furthermore, by accounting for the effect of bleeding off bypass air for the fluid inserts in the LES simulation, this noise reduction is predicted to be achieved at a conservative thrust loss estimate of under 2% at both laboratory and afterburner operating conditions.

Experimental study of heat transfer with a jet flow in the complex space of small steel containment

To study the heat transfer phenomenon in the complex space of small steel containment during the jet flow, the experiments and simulation were conducted with various jet inlet temperatures, velocities, and heights. The results show the flow field and temperature field are quite different from the large containment. There is no obvious thermal stratification phenomenon in small containment during the jet flow. The temperature in the lower part of the containment which is below the jet almost uniform. The temperature filed above the jet is more complex and depends on many factors. With the jet temperature increases, the temperature field above the jet increases obviously and the lower part increases slightly. The higher jet velocity, the higher initial kinetic energy, and the flow are easy to reach the dome and form a circulation.

Large eddy simulation of acoustic waves generated from a hot supersonic jet

The effects of jet temperature on acoustic waves generated by a supersonic jet are investigated using large eddy simulation (LES) based on a high-fidelity computational code. The sixth-order compact scheme and the fourth-order Runge–Kutta scheme are employed for spatial derivatives and time integration, respectively. First, a verification and validation study is conducted using simulations of a cold supersonic jet with a jet Mach number of 2.0 and Reynolds number of $$9.0 \times 10^5$$, and the effects of grid resolution and disturbance strength are evaluated. The verification and validation study shows that $$6.5 \times 10^8$$ grid points are sufficient for qualitative discussion of acoustic wave generation phenomena and that the addition of disturbances is important for suppressing the acoustic waves caused by the turbulent transition at the nozzle exit, as seen in previous studies for a subsonic jet. Then, LESs of supersonic jets with a jet Mach number of 2.0 and Reynolds number of $$9.0 \times 10^5$$ are performed for three temperature cases where the ratios of chamber to atmospheric temperature are 1.0, 2.7, and 4.0. The present results illustrate that different jet temperatures do not change the shear layer thickness, but the shear layer develops more inside the jet as the jet temperature increases, resulting in a shorter potential core for the hot jet. With regard to the acoustic fields, as the jet temperature increases, stronger Mach waves are emitted from a wider source region at wider radiation angles. We observe multiple Mach waves with different angles in the hot jet cases.

Study on plasma ablation behavior of C/C composite materials under particle erosion

In order to explore the ablation law and characteristics of carbon/carbon composite materials on the surface thermal protection of hypersonic vehicles under the condition of particle erosion, the ablation test of a 4D C/C composite was carried out based on a small plasma simulated ablation test system. Four sets of experiments were designed according to different temperature and particle concentration. After the test, two kinds of ablation rate were measured, and the microscopic ablation morphology was observed by scanning electron microscope (SEM) and the ablation behavior was analyzed. The results show that, under the equivalent test conditions, the rate of jet temperature increases, and the material ablation rate increases. With the increase of particle concentration, the two kinds of ablation rate of materials increased, the maximum mass ablation rate was 0.0363 g·s−1, and the line ablation rate was 0.053 mm·s−1. The temperature affects the thermal erosion rate of the material, while the particle mainly causes mechanical erosion. The particle has a coupling effect of heat transfer and mechanical destruction on the material, and the material ablation is intensified. Moreover, due to the strong corrosion resistance of carbon fiber, the overall corrosion resistance of materials has obvious anisotropy.

Thermal protection performance of opposing jet generating with solid fuel

A light and small gas supply device, which uses fuel gas generating with solid fuel as coolant gas, is introduced for opposing jet thermal protection in hypersonic vehicles. A numerical study on heat flux reduction in hypersonic flow with opposing jet is conducted to investigate the cooling efficiency of fuel gas. Flow field and cooling efficiency at different jet temperatures, as well as the effect of fuel gas, are determined. Detailed results show that shock stand-off distance changes with an increase in jet pressure ratio and remains constant with an increase in jet temperature. Cooling efficiency weakens with an increase in jet temperature and can be strengthened by enhancing jet pressure. Lastly, a remarkable heat flux reduction is observed with fuel gas injection with respect to no fuel gas injection when jet temperature reaches 900 K, thereby proving the positive cooling efficiency of fuel gas.

Entropy generation concept for a turbulent plane jet with variable density

This study presents a numerical investigation of the entropy generation of a turbulent plane jet with variable density. Turbulent simulations are carried out using the first order k-ε turbulence model. The Finite Volume Method (FVM) is used to discretize governing equations. The effect of the jet temperature at the inlet nozzle on the flow and mainly on the entropy generation has been studied. So far, a comparison of numerical and experimental results gives a satisfactory agreement. The present investigation suggests that high value of entropy generation correspond to the higher inlet hot jet temperature. Moreover, the viscous dissipation is found to be important near the nozzle exit and it becomes negligible in the affinity region of the jet. Furthermore, the entropy generation rate as well as the Merit number grows progressively to reach an asymptotic value along the flow direction as the inlet jet temperature increases.

Numerical analysis of characteristics of multi-orifice nozzle hydrothermal jet impact flow field and heat transfer

Hydrothermal jet technology is a new drilling method in which the rocks are broken by the combination of thermal spallation and high velocity impact effect. This technology uses a high temperature and high velocity jet to break rocks and has the potential to be more economically advantageous than conventional techniques for geothermal well drilling. Previous related studies primarily examine numerical simulation on one hydrothermal jet flow field, and to the best of our knowledge, no specific study addresses the thermo-physical interaction between wellbore fluid and ambient rock. This paper presents a multi-orifice nozzle model to investigate the features of a flow field with multiple hydrothermal jets and the heat transfer to ambient rocks. A transient impact flow field with multiple hydrothermal jets is analyzed in terms of axial temperature, bottomhole temperature, and bottomhole pressure. Also, downhole velocity field is specifically investigated. Next, influences of time, jet temperature, and jet pressure difference on the flow field and heat transfer between wellbore fluid and ambient rocks are predicted and compared. The results indicate that the bottomhole central temperature and pressure are higher than the two sides under multiple hydrothermal jets conditions, which is similar to the flow pattern with a single jet. Moreover, the distribution of axial velocity has three peaks at cross-sections, and the centerline axial velocity is the highest. There is a negative relationship between the maximum radial velocity and the ratio between axial distance and nozzle diameter (L/D). Also, the position of the maximum radial velocity moves to the side wall as the ratio (L/D) increases. Second, the bottomhole temperature increases uniformly with increase in jet temperature. The bottomhole temperature becomes decreasingly sensitive to the variance of pressure difference, and the bottomhole pressure exhibits a ladder distribution. Finally, while an increase in either jet temperature or pressure difference can enhance the multiple hydrothermal jets heat transfer effect, increasing the jet temperature is considerably more effective. All of these results are beneficial to the parameters design for the hydrothermal jet drilling technology.

Using an energized oxygen micro-jet for improved graphene etching by focused electron beam

We report on an improved Focused Electron Beam Induced Etching (FEBIE) process, which exploits heated oxygen delivery via a continuous supersonic micro-jet resulting in faster graphene patterning and better etch feature definition. Positioning a micro-jet in close proximity to a graphene surface with minimal jet spreading due to a continuous regime of gas flow at the exit of the 10 μm inner diameter capillary allows for focused exposure of the surface to reactive oxygen at high mass flux and impingement energy of a supersonic gas stream localized to a small etching area exposed to electron beam. These unique benefits of focused supersonic oxygen delivery to the surface enable a dramatic increase in the etch rate of graphene with no parasitic carbon “halo” deposition due to secondary electrons from backscattered electrons (BSE) in the area surrounding the etched regions. Increase of jet temperature via local nozzle heating provides means for enhancing kinetic energy of impinging oxygen molecules, which further speed up the etch, thus minimizing the beam exposure time and required electron dose, before parasitic carbon film deposition due to BSE mediated decomposition of adsorbed hydrocarbon contaminants has a measurable impact on quality of graphene etched features. Interplay of different physical mechanisms underlying an oxygen micro-jet assisted FEBIE process is discussed with support from experimental observations.

Experimental investigation on heat transfer of HEMJ type divertor with narrow gap between nozzle and impingement surface

In order to explore the possibility of improvement of the He-cooled modular divertor with multiple jet cooling (HEMJ) concept including optimization of design parameter, an experimental study on heat transfer performance of the HEMJ divertor was performed by means of helium loop at Georgia Tech, in which the pressure, flow rate and temperature of helium pressure is up to 10MPa, 8g/s and 300°C, respectively, under heat flux of 6MW/m2 loaded by means of induction heater. Although the non-dimensional distance between jet nozzle and impingement surface H normalized by typical nozzle diameter D, H/D is 0.9 in the reference design of HEMJ, heat transfer experiments were carried out under the condition of H/D=0.5 and 0.25 to enhance the heat transfer performance. In the case of H/D=0.25, the averaged Nusselt number was increased by about 20% from the value for H/D=0.5 in the case that the jet temperature less than 100°C. By contraries, the averaged Nusselt number was decreased with increase in jet temperature which is larger than 200°C in the H/D=0.25 case. It is expected that the degradation of heat transfer performance with increasing the jet temperature is caused by the re-laminarization occurred near heat transfer surface.

Experiment on rock breaking with supercritical carbon dioxide jet

Abstract Rock breaking with SC-CO2 has the advantages of low threshold pressure and high rate of penetration, so it has attracted full attention. In order to clarify the law of rock breaking with SC-CO2 jet, and enable it to serve SC-CO2 drilling better, the SC-CO2 jet system for rock breaking was used to carry out the experiments, which demonstrated that jet pressure, jet temperature, confining pressure, jet distance, rotary speed of core samples and jet time are the main factors to influence the rock-breaking performance and efficiency. The results showed the effects as follows. Jet pressure and confining pressure are the direct factors to affect rock-breaking performance. With the increase of jet pressure, the rock-breaking efficiency increases gradually, while as the confining pressure increases, it decreases with constant jet pressure or has the maximum around the critical jet pressure with constant pressure difference. With the increase of jet temperature, the efficiency increases at first and then decreases, and the relationship curve showed in parabolic function. Under the experimental conditions in this paper, the optimal jet distance is about 3–4 times of nozzle diameter. The rotary speed of core sample has no substantial influence on the erosion depth, but on the average width or diameter of eroded grooves. The average width and the size of the eroded cuttings are smaller when the rotary speed is higher. The erosion depth increases but the trend gradually decreases with the jet time being prolonged.

Unique Characteristics of Cryogenic Nitrogen Jets Under Supercritical Pressures

Two-dimensional planar and three-dimensional round nitrogen jets under supercritical pressures are simulated with a wide range of conditions to explore their unique characteristics. A high-order method using a sixth-order compact scheme is applied. The present study parametrically covers two supercritical pressures of 4 and 8 MPa and three jet injection temperatures between a cryogenic jet of 82 K and a warmer jet of 133 K. Unique characteristics are found in both the mean temperature and temperature fluctuation profiles on the centerline (i.e., slower increase of jet temperature and relatively weak temperature fluctuation), only in the case of a near-critical pressure of 4 MPa and a cryogenic jet of 82 K. For the condition, the temperature profile on the centerline uniquely consists of four characteristic regions. The other conditions show no distinct features. The present study suggests that the distributions of the specific heat capacity at constant pressure help to explain the generation of the unique temperature characteristics.

Characteristics of the Shock Noise Component of Jet Noise

The characteristics of the flow and the noise of shock-containing jets have been studied for nearly three decades. It is now established that broadband shock-associated noise is generated by the interaction of the downstream-convecting coherent structures of the jet flow with the shock cells in the jet plume. Past analyses of far-field data have been carried out with the total measured noise, which contains both the turbulent mixing noise and shock noise. In this study, these two components are first separated and extracted from the total spectra. Both convergent and convergent-divergent nozzles are considered. The decomposition is made possible by a recently developed scaling methodology for turbulent mixing noise, which provides excellent collapse of the mixing noise spectra from jets at all velocities but at a fixed temperature ratio. The characteristics of the shock component alone are investigated. A surprising effect of jet temperature on shock noise is established for the first time: the levels increase as the jet is first heated; however, the levels do not increase with further increase in jet temperature. The physical phenomenon responsible for this saturation of levels is not known at this time. The intensity for shock noise in the forward quadrant does not scale as the fourth power (shock exponent) of √|M 2 j -M 2 D | but spans a range from 2.9 to 6.17, depending on the radiation angle and the jet temperature ratio. It is not straightforward to collapse the shock spectra. It is also established for the first time that nonlinear propagation effects are manifested at lower radiation angles, in which the shock component is dominant. The physical phenomenon that triggers the onset of nonlinear propagation for the shock noise could not be identified. The characteristics of the correlation functions at the lower inlet angles for subsonic and supersonic jets are different, attesting to the different noise generation mechanisms.

Criteria for the existence of helical instabilities in subsonic impinging jets

Understanding instability modes in impinging jets is important for the design of advanced vertical takeoff and landing aircraft. Our initial experimental observations of helical modes in subsonic impinging jets were contrary to expectations based on published stability theory results. This paper focuses on the curious phenomenon of the occurrence of these, hitherto unexpected, helical modes in subsonic impinging jets and provides, both experimental and analytical proof for their existence. Past results, based on linear stability analysis, that call for an absence of helical modes in cold, subsonic impinging jets have been re-examined to reconcile new experimental data. Based on this re-examination, a new threshold Mach number has been proposed, above which helical modes are permissible. The revised theory put forth in this paper indicates that the threshold Mach number for the existence of the helical mode depends on the jet temperature and that this threshold decreases as the jet temperature increases. This threshold Mach number has been experimentally verified for unheated jets. Additionally, the experimental results reveal that the threshold Mach number also depends on the stand-off distance. Finally, it has been shown that the experimentally obtained mean Strouhal numbers for the helical mode show excellent agreement with the Strouhal number of the least dispersive wave of the same mode calculated at various Mach numbers. The results presented here offer hope for better understanding of impinging jet instability modes.

Dimensional Analysis of Jet Noise Data

*A formula for scaling laboratory model jet noise data to that of a full size jet engine is established. This is done by dimensional analysis and the Buckingham P theorem. It is well known that the noise intensity radiated by a jet varies as a high power of its velocity. This power law dependence is supported by theory and experiment. The most famous power law is the Lighthill U 8 law. In this work, a dimensionless form of the power law is sought and developed. Through the use of this nondimensional form power law, a “hot jet” limit is found at high jet temperature. In the hot jet limit, the velocity exponent and the proportionality constant of the power law are insensitive to further increase in jet temperature. This is a somewhat surprising result. Experimentally, it has been observed that seasonal temperature variation can lead to a 1.5 to 2.0 dB change in jet noise intensity. Here, environmental effects on jet noise such as seasonal and altitude variations are studied through results established by dimensional analysis. Finally, a way to scale jet mixing noise from perfectly expanded jets to shock containing jets is proposed.

Shock leakage through an unsteady vortex-laden mixing layer: application to jet screech

In an under-expanded supersonic jet, the interaction between shock-cell structure and vortices in a mixing layer generates intense tonal noise, called jet screech. This noise generation can be explained as a shock-leakage process through an unsteady vortex-laden mixing layer. This paper studies the shock-leakage mechanism based on a geometrical theory and direct numerical simulation (DNS) in two dimensions. In the limit of weak shocks, the analysis becomes analogous to geometrical acoustics: the eikonal equation demonstrates that shock waves tend to leak near the saddle points between vortices. Analysing the wavenumber vector, it is shown that the local vorticity behaves as a barrier against shocks. Using the unsteady DNS data, trajectories of the shock fronts are computed with the time dependent eikonal equation. Furthermore, the interaction between unsteady vortices and a compression wave is solved using DNS. The geometrical theory shows good agreement with DNS for shock-front evolution, but the amplitude of the leaked waves agrees only qualitatively. This study also investigates the effects of a temperature difference across the mixing layer. The analysis based on total internal reflection and the numerical results of both geometrical acoustics and DNS indicate that the direction of the radiated shock noise tends to rotate downstream as the jet temperature increases.

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.

Screech tones from free and ducted supersonic jets

It is well known that screech tones from supersonic jets are generated by a feedback loop. The loop consists of three main components. They are the downstream propagating instability wave, the shock cell structure in the jet plume, and the feedback acoustic waves immediately outside the jet. Evidence will be presented to show that the screech frequency is largely controlled by the characteristics of the feedback acoustic waves. The feedback loop is driven by the instability wave of the jet. Thus the tone intensity and its occurrence are dictated by the characteristics of the instability wave. In this paper the dependence of the instability wave spectrum on the azimuthal mode number (axisymmetric or helical/flapping mode, etc.), the jet-to-ambient gas temperature ratio, and the jet Mach number are studied. The results of this study provide an explanation for the observed screech tone mode switch phenomenon (changing from axisymmetric to helical mode as Mach number increases) and the often-cited experimental observation that tone intensity reduces with increase in jet temperature. For ducted supersonic jets screech tones can also be generated by feedback loops formed by the coupling of normal duct modes to instability waves of the jet. The screech frequencies are dictated by the frequencies of the duct modes. Super resonance, resonance involving very large pressure oscillations, can occur when the feedback loop is powered by the most amplified instability wave. It is proposed that the observed large amplitude pressure fluctuations and tone in the test cells of Arnold Engineering Development Center were generated by super resonance. Estimated super-resonance frequency for a Mach 1.3 axisymmetric jet tested in the facility agrees well with measurement.