Jet Nozzle Exit Research Articles

Analysis of Sound Propagation Behaviors for Supersonic Jet on Far Field Region by Computational Aero-Acoustics (CAA) Simulation

Noise emission is an essential issue for the aviation industry, as it harms health and induces various physiological responses. The noise generated by supersonic jets is very intense. It will cause fatigue and even damage the human hearing system in the surrounding area of jet operation. Besides, the experimental and prototyping cost for the jet model is prohibitive, and it is a vast project and process that takes a lot of time to run. The purpose of this study is to determine the sound propagation behaviours of a supersonic jet in the far-field region and to analyse the consequences of the velocity of a supersonic jet on sound propagation of supersonic jet by using computational fluid dynamics (CFD) and computational aeroacoustics (CAA) simulations. This study focused on the perspective of observing the distance of the receiver when receiving the sound propagation of a supersonic jet, the observed angle of the receiver when receiving the sound propagation of a supersonic jet, and the velocity of the supersonic jet. The CFD and CAA analyses were performed in transient state simulation and the 2-inch Acoustics Reference Nozzle (ARN2). The result shows that the overall SPL throughout the frequency is proportional to the jet velocity of the supersonic jet. However, the distance and angle of the receiver gave different results in sound propagation behaviour. The results also conclude that as the distance between the receiver and jet nozzle exit increases, the overall SPL trend will decrease throughout the frequency increase. As the vertical distance between the receiver and the axisymmetric line of the jet nozzle increases, the frequency of the receiver starts to observe will decrease.

Optical emission spectroscopy of an industrial thermal atmospheric pressure plasma jet: Parametric study of electron temperature

The plasma parameters of an industrial atmospheric pressure plasma jet (APPJ) are measured as a function of the electric power of the plasma generator, the gas flow, and the distance from the jet nozzle exit. The APPJ device operates an electric discharge under Argon gas flow resulting into a continuous Argon plasma jet in the kW power range expanding into ambient air. The plasma temperature Te and electron number density Ne are determined by optical emission spectroscopy (OES) analyzing up to 17 emission lines of neutral Ar (I) and singly-ionized Ar (II) species using the Saha-Boltzmann plot (SBP) method. For the accurate determination of plasma parameters a methodology is developed to overcome fundamental limitations in OES of Argon plasma that is due to the strongly different intensities of Ar (I) and Ar (II) emission lines. The most significant step is the use of spectral bandpass filters in the optical collection system. The experimental parameters of the jet device are playing a crucial role for APPJ applications (e.g. thermal load to the workpiece, plasma chemistry interaction etc.). We measure Te and Ne in dependence of the experimental parameters and obtain consistent and accurate values of Te = 9000 ± 150 K and Ne = 5 × 1015 cm−3 (typ.). For comparison, plasma characterization using only the neutral Ar lines gives inaccurate and inconsistent Te values. This highlights the importance of using also the ionic Ar lines. The developed methodology may be diversified and applied also for OES of other rare gas plasma.

Measurement of turbulent supersonic steam jet flow characteristics using TDLAS

Ejectors have no moving parts and are preferable to mechanical compressors in many applications, but ejectors typically have a relatively low efficiency. To aid in the ejector design process, thorough understanding of the turbulent mixing of multi-phase compressible jets is beneficial.This paper reports experimental results for Tunable Diode Laser Absorption Spectroscopy (TDLAS) measurements derived from an axisymmetric supersonic steam jet apparatus.In this experimental work, a supersonic steam jet nozzle exit of a diameter 13.6 mm was surrounded by a low-speed flow of dry nitrogen. The TDLAS system was traversed through the flow at three different planes downstream from the ejector nozzle exit: 15, 20, and 30 mm distance. At each of the three planes, line-of-sight measurements were made with the laser passing through locations between 0 and 15 mm from the jet centreline.Through the analysis of the TDLAS data and application of the Abel inversion method, the radial distribution of the pressure, temperature, and the concentration of the water-vapour were obtained. The key findings are that it is possible to determine key physical parameters using experimental TDLAS measurements when combined with a suitable numerical optimization approach.

Linear and nonlinear modelling of far-field propagation of broadband shock-associated noise

A triple-scale computational model is implemented to simulate noise generated by a supersonic under-expanded screeching jet corresponding to the LTRAC (Laboratory for Turbulence Research in Aerospace and Combustion) experiment at different distances from the source. The investigation is focused on the broadband-associated noise, which is a prominent feature of the acoustic field of the LTRAC jet. In the jet near-field, the compressible Navier–Stokes equations are solved using the high-resolution CABARET Large Eddy Simulation (LES) method accelerated on Graphics Processing Units. The LES solution is substituted in the Ffowcs Williams–Hawkings (FW–H) model to obtain the noise solution in the acoustic mid field at 20 initial jet diameters from the jet nozzle exit. The mid-field acoustic solution is used as the input for the spherical generalised Burgers’ equation. The general form of Burgers’ equation is solved numerically in the frequency domain for a wide range of observer distances up to 18 million initial jet diameters, where viscous dissipation fully dominates for most frequencies. To answer the question if the nonlinear acoustic wave propagation effects for the LTRAC jet are important, the nonlinear and linear solutions of Burgers’ equation are compared.

Flow and Acoustic Fields of Rocket Jets Impinging on a Perforated Plate

The flow and acoustic fields of jets at a Mach number of 3.1 impinging on a plate at of the jet nozzle exit, where is the nozzle diameter, have been investigated using highly resolved large-eddy simulations. The plate is perforated with a hole of diameter , , , or . The full-plate and free-jet cases have also been considered. The pressure levels are highest for the non-perforated plate and decrease as the hole diameter increases. Compared with the free jet, they are higher by about 5 dB for the full plate, 4 dB for and , 3 dB for , and 2 dB for . In the upstream direction, the broadband shock-associated noise is prevailing for the free jet. For the impinging jets, the main noise component in that direction is produced by the impingement of the jet turbulent structures on the plate. In the downstream direction, for the free jet and down to the plate for the impinging jets, the sound field is dominated by Mach waves. Downstream of the perforated plates, waves are generated by interactions between the jet flow and the plate.

Nonlinear scattering of crossed ultrasonic beams in the presence of a turbulent bubbly jet flow in water

Experiments involve the nonlinear scattering of mutually perpendicular crossed ultrasonic beams of primary CW frequency components: f1 = 2.240 MHz, f2 = 2.293 MHz; interacting nonlinearly with turbulent bubbly shear flow generated by a circular water jet (nozzle exit diameter D = 1.6 mm and volume flow rate 32 cc/s). The jet axis is perpendicular to the crossed beam axes. The nozzle exit is downward (5 mm above the surface). The water pump’s suction port was at the bottom center of the 10 cm cubic acrylic water tank (wall thickness 4.8 mm). Identical 1.27 cm diameter quartz transducers (T1 and T2) were epoxied at the centers of adjacent vertical tank sidewalls generate the primary beams (in the i or j directions). Identical 4.5MHz receiving transducers (6.35 mm diam PZT-4) measure nonlinear scattering in the forward or backscattered directions. Receiver Rf located in the plane formed by the primary acoustic beam axes) detects in the i cos 45 + j sin 45 direction. Receiver Rb was located in the opposite direction. In the absence of turbulence virtually no radiated sum frequency component exists. Doppler shift, frequency broadening, skewness and kurtosis from the received sum frequency power spectrum were measured.

Some Characteristics of Compressible Air Impingement Jet Applied in Pneumatic Dimensional Control

The present paper studies the impingement of compressible air jet on a flat plate primarily from the aspect of its application in the domain of pneumatic metrology, i.e. in cases of small distance between the jet nozzle exit and the flat plate. Besides this direct application in the area of pneumatic metrology, the distance between the nozzle exit and the flat plate has been considerably increased and the case of a free jet was analysed with a view to compare the results applicable in various domains. This experimental study demonstrates that the structures of a free jet and this special case of an impingement jet are totally different. In the pressure distribution of the impingement jet, pressure discontinuity above the flat plate may occur, which is shown to be the result of low intensity shock waves and transonic flow. The experimental results show that the pneumatic sensitivity of a pneumatic comparator is a function of the supply pressure and the internal orifice diameter, as well as that the impingement air jet is a typical case of non-isentropic flow.

Experimental and Numerical Study of Jet Impingement Cooling for Improved Gas Turbine Blade Internal Cooling With In-Line and Staggered Nozzle Arrays

Abstract Internal cooling of gas turbine blades is performed with the combination of impingement cooling and serpentine channels. Besides gas turbine blades, the other turbine components such as turbine guide vanes, rotor disks, and combustor wall can be cooled using jet impingement cooling. This study is focused on jet impingement cooling, in order to optimize the coolant flow, and provide the maximum amount of cooling using the minimum amount of coolant. The study compares between different nozzle configurations (in-line and staggered), two different Reynold's numbers (1500 and 2000), and different stand-off distances (Z/D) both experimentally and numerically. The Z/D considered are 3, 5, and 8. In jet impingement cooling, the jet of fluid strikes perpendicular to the target surface to be cooled with high velocity to dissipate the heat. The target surface is heated up by a direct current (DC) power source. The experimental results are obtained by means of thermal image processing of the captured infra-red (IR) thermal images of the target surface. Computational fluid dynamics (CFD) analysis were employed to predict the complex heat transfer and flow phenomena, primarily the line-averaged and area-averaged Nusselt number and the cross-flow effects. In the current investigation, the flow is confined along with the nozzle plate and two parallel surfaces forming a bi-directional channel (bi-directional exit). The results show a comparison between heat transfer enhancement with in-line and staggered nozzle arrays. It is observed that the peaks of the line-averaged Nusselt number (Nu) become less as the stand-off distance (Z/D) increases. It is also observed that the fluctuations in the stagnation heat transfer are caused by the impingement of the primary vortices originating from the jet nozzle exit.

Adjoint sensitivity and optimal perturbations of the low-speed jet in cross-flow

The tri-global stability and sensitivity of the low-speed jet in cross-flow are studied using the adjoint equations and finite-time horizon optimal disturbance analysis at Reynolds number $Re=2000$, based on the average velocity at the jet exit, the jet nozzle exit diameter and the kinematic viscosity of the jet, for two jet-to-cross-flow velocity ratios $R=2$ and $4$. A novel capability is developed on unstructured grids and parallel platforms for this purpose. Asymmetric modes are more important to the overall dynamics at $R=4$, suggesting increased sensitivity to experimental asymmetries at higher $R$. Low-frequency modes show a connection to wake vortices. Adjoint modes show that the upstream shear layer is most sensitive to perturbations along the upstream side of the jet nozzle. Lower frequency downstream modes are sensitive in the cross-flow boundary layer. For $R=2$, optimal analysis reveals that for short time horizons, asymmetric perturbations dominate and grow along the counter-rotating vortex pair observed in the cross-section. However, as the time horizon increases, large transient growth is observed along the upstream shear layer. When $R=4$, the optimal perturbations for short time scales grow along the downstream shear layer. For long time horizons, they become hybrid modes that grow along both the upstream and downstream shear layers.

Investigation of the effect of turbulence intensity and nozzle exit boundary layer thickness on stability pattern of subsonic jet

In this study, factors affecting the noise generation by instability waves in a subsonic jet with acoustic Mach number of 0.5 are investigated using linear stability analysis. The base flow required for instability analysis is obtained by modeling the jet stream based on the k-ε turbulence model and using the empirical coefficients suggested by Thies and Tam [1]. The resulting base flow profiles are used to solve the linear instability equation, which governs the pressure perturbation for obtaining the eigenvalues and eigenfunctions. The results of linear instability analysis for phase and amplitude of pressure fluctuations are compared against the existing experimental data, which demonstrated the validity of the conducted instability analysis. The effects of turbulence intensity and thickness of the boundary layer at the jet nozzle exit on the results of the linear instability analysis are investigated. The results show that as the turbulence intensity at nozzle exit increases, the frequency range for which the spatial growth rates are positive grows smaller, and except for very low frequencies, this leads to decreased growth rates in both axisymmetric and first azimuthal modes. Also, in both of these modes, an increase in the thickness of the boundary layer at nozzle exit leads to a decrease in perturbation's growth rates in the surveyed frequency ranges.

Particle image velocimetry and infrared thermography of turbulent jet impingement on an oscillating surface

Jet impingement is widely used for forced-convection heat transfer applications and knowledge about its flow structure and heat transfer rate on a static surface are well established. However, the characteristics of jet impingement on an oscillating surface are relatively unknown. This study experimentally investigates the effect of surface oscillation on the fluid dynamics and heat transfer of an unconfined turbulent impinging jet. The Reynolds numbers of the axisymmetric jet are 5000 and 10,000, based on the jet-nozzle exit diameter, and the surface is placed at nominal standoff distances of 2 and 5 diameters from the jet-nozzle exit. The surface oscillates in a direction parallel to the jet axis at frequencies of 20 Hz and 50 Hz and at a peak-to-peak displacement amplitude of 0.2 times the jet-nozzle exit diameter. The phase-average and mean flow characteristics at six phases through the surface oscillation cycle, and the steady-state mean heat transfer rate at the oscillating surface, are determined using particle image velocimetry and infrared thermography respectively. These are analyzed and compared with the mean flow and heat transfer characteristics for jet impingement on a static surface. Surface oscillation directly affects the mean axial jet velocities and thence the mean radial velocities, and this effect is greater at locations in the flow-field closer to the surface. This gives rise to lower mean axial and radial strain rates in the impingement region and lower turbulence intensities in the wall-jet region when compared with those for a static surface. The frictional interaction between the impinging jet and oscillating surface induces higher surface temperatures than those on a static surface. These factors reduce the heat transfer rate for jet impingement on an oscillating surface when compared with that on a static surface. The reduction is greater in the impingement region than in the wall-jet region with the stagnation point Nusselt number for an oscillating surface being lower by a maximum value of 15%. Overall, for the range of parameters considered in this study, these findings suggest that surface oscillation in jet impingement weakens the transport phenomena capabilities from those present in the case of a static surface.

Effect of Jet Oscillation on the Maximum Impingement Plate Skin Friction

The maximum impingement plate skin friction and flow field is measured for an acoustically forced planar impinging gas jet using oil film interferometry (OFI) and particle image velocimetry (PIV), respectively. The study is performed at a jet Reynolds number of Rejet = 11,000 and an impingement distance H, which is set to eight times the nozzle width W. The planar impinging gas jet is forced at the jet nozzle exit using Strouhal numbers StH = 0.39, 0.76, and 1.1, which are similar to those associated with the jet-plate tones measured in air-knife wiping experiments. The flow-field measurements indicate that the jet column oscillates at the applied forcing frequency, and depending on the forcing frequency, organized vortex structures can be identified in the shear layers that impinge on the plate surface. Both of these jet oscillation features result in a reduction in the time-averaged maximum impingement plate skin friction. This skin friction reduction is attributed to momentum loss at the jet centerline caused by increased levels of fluid entrainment and mixing of the surrounding quiescent fluid.

NO Emission of a Non-premixed Oxygen-Enhanced Flame in Burned Gas Entrainment above the Self-Ignition Temperature (BEST) Conditions

ABSTRACTThe emission characteristics of non-premixed oxy-fuel and oxygen-enhanced flames in burned gas entrainment above the self-ignition temperature (BEST) conditions were experimentally investigated in a lab-scale slot-type combustor. The inside geometry of the furnace was width = 250 mm, depth = 250 mm, and height = 350 mm. A slot-type burner was located on the center of the furnace bottom. The widths of the fuel jet and oxidizer nozzle exit were 0.24 mm and 0.52 mm. The separation distance between the nozzle exits was 8 mm and the depth of the nozzle exit was 20 mm. Light emission data were obtained with a digital single lens reflex camera, spectrometer, and intensified charge-coupled device camera to visualize the flame appearance in a furnace. The distribution of the furnace temperature in the BEST conditions was measured with R-type thermocouples. The pollutant emission trend was analyzed when the inlet velocity for fuel jet and oxidizer is 10 m/s to 30 m/s and 10 m/s to 55 m/s, the volumetric mole fraction of oxygen in an oxidizer is 40% to 100%, and the global equivalence ratio is 0.55 to 1.03. The objectives of the present work were to study the flame spectra in normal temperature and pressure (NTP) and the BEST conditions and to determine the global production rate of nitrogen oxides in non-premixed oxy-fuel and oxygen-enriched flames. The visible flame of a non-premixed oxy-methane flame disappeared and temperature deviation in a furnace decreased by 300°C in the BEST conditions. The global production rate of nitrogen oxides ([NOx]/τG) level decreased while increasing the volumetric mole fraction of oxygen in an oxidizer. The slope of [NOx]/τG was similar to that of a non-premixed methane-air flame in NTP conditions. The level of [NOx]/τG was lower in oxygen-enriched flames than in CH4-air flames.

Capillary jet breakup by noise amplification

A liquid jet falling by gravity ultimately destabilizes by capillary forces. Accelerating as it falls, the jet thins and stretches, causing a capillary instability to develop on a spatially varying substrate. We discuss quantitatively the interplay between instability growth, jet thinning and longitudinal stretching for two kinds of perturbations, either solely introduced at the jet nozzle exit or affecting the jet all along its length. The analysis is conducted for any values of the liquid properties for a sufficiently large flow rate. In all cases, we determine the net gain of the most dangerous perturbation for all downstream distances, thus predicting the jet length, the wavelength at breakup and the resulting droplet size.

Mathematical modelling and characteristics of the pilot valve applied to a jet-pipe/deflector-jet servovalve

The accurate model of the jet-type valve, as the pilot control stage of a jet-pipe/deflector-jet servovalve, is of great significance to analyze and design a servovalve. However, the flow field in the jet-type valve is too complex to build an accurate mathematical model. In this paper, the collision between the liquid and the jet is supposed as the impact of jet on a moving piston, which makes a complex the fluid mechanical problem become simple. Based on this assumption, a model of the jet-type valve is developed in this paper. Unlike the previous models, the structural parameters, the distance between the jet-nozzle exit and receiving surface, the included angle between two receiver holes as well as the distance between two receiver holes, all can be considered in this model. To test and verify the theoretical model, the pressure and flow characteristic curves of a jet-type valve are given by the methods of flow filed numerical simulation and experiment.As shown by the verification results, the theoretical pressure characteristic curve is very approximate with the experimental data and numerical simulation, while the flow characteristic curves need to be modified and the modified model is valid.

Effect of guide wall on jet impingement cooling in blade leading edge channel

The characteristics of fluid flow and heat transfer, which are affected by the guide wall in a jet impinged leading edge channel, have been investigated numerically using three-dimensional Reynolds-averaged Navier–Stokes analysis via the shear stress transport turbulence model and gamma theta transitional turbulence model. A constant wall heat flux condition has been applied to the leading edge surface. The jet-to-surface distance is constant, which is three times that of the jet diameter. The arrangement of the guide wall near the jet hole is set as a variable. Results presented in this study include the Nusselt number contour, velocity vector, streamline with velocity, and local Nusselt number distribution along the central line on the leading edge surface. The average Nusselt number and average pressure loss between jet nozzle and channel exit are calculated to assess the thermal performance. The application of the guide wall is aimed at improving heat transfer uniformity on the leading edge surface. Results indicated that the streamwise guide wall ensures the vertical jet impingement flow intensity and prevents the flow after impingement to reflux into jet flow. Thus, a combined rectangular guide wall benefits the average heat transfer, thermal performance and heat transfer distribution uniformity.

Noise of an Overexpanded Mach 3.3 Jet: Non-Linear Propagation Effects and Correlations with Flow

The noise emitted by an overexpanded round jet at a Mach number of 3.3 and a Reynolds number of 105, computed in a previous study using large-eddy simulation (LES), is investigated. In a first step, the non-linear sound propagation effects are quantified by performing two far-field wave extrapolations from the LES near-field data. The extrapolations are carried out by solving the linearized Euler equations in one case and the full Euler equations in the other, without atmospheric absorption, up to a distance of 240 radii from the jet nozzle exit. The non-linear effects are shown to be quite significant, resulting in a series of N-shaped waves in the pressure signals, and in weaker mid-frequency components and stronger high-frequency components in the spectra. Close to the peak directivity radiation angle, for instance, they lead to about a 8 dB loss and a 6 dB gain at the Strouhal numbers of 0.2 and 1, respectively. In a second step, noise generation mechanisms are discussed by calculating correlations between far-field pressure fluctuations and turbulent quantities in the jet. High levels of correlation are found with the centerline flow fluctuations at the end of the potential core, with the shear-layer flow fluctuations over a large axial distance, and with the centerline density fluctuations between the 3rd and the 5th shock cells. They are attributed to the intermittent intrusion of low-speed vortical structures in the potential core, to the supersonic convection of turbulent structures, and to the shock motions at the screech tone frequency.

One-Equation Extended Nonlinear Turbulence Modeling in Predicting Three-Dimensional Wall Jets

To predict the flowfield of three-dimensional wall jets, an extended nonlinear constitutive relation is incorporated into the Spalart–Allmaras turbulence model. A modification of the model is made to improve the predictability of free jets. The FaST aerodynamic routines code, developed at the Japan Aerospace Exploration Agency, is used as a compressible-flow solver. First, a turbulent boundary-layer flow along a flat plate is computed to confirm the validity of the extended nonlinear constitutive relation. The obtained logarithmic velocity profile agrees well with the analytical solution. As a result, the modification is confirmed to have no adverse effects on the prediction of the typical wall-bounded flow. Second, computations of three-dimensional free and wall jets are performed, the results of which are compared with observations of the velocity field up to the far region from the jet nozzle exit, which are made by the experimental facility of Nagoya University. In free jets, reasonable computed results are obtained with respect to the streamwise decay and the half-width of the velocity, confirming the applicability of the modification to free jets. In wall jets, the modified model properly reproduces the secondary flow observed in the experiment, and its qualitative success is shown by the conservation of momentum.

The effect of CO2 addition on the flame behavior of a non-premixed oxy-methane jet in a lab-scale furnace

The dilution effect of carbon dioxide (CO2) in an oxidizer was studied experimentally in a non-premixed oxy-methane flame. A lab-scale furnace with a slot-type burner was used as a model of an industrial furnace. The objectives of the current study are to investigate the flame stabilization, to analyze the flame spectra, and to study the flame behavior of non-premixed oxy-methane flames as the CO2 mole fraction is varied in an oxidizer. The flame stabilization was estimated by changing the flow velocity at the fuel jet nozzle exit (uF) and the oxygen nozzle exit (uOx) from uF=7–50m/s for methane (CH4) and from uOx=10–120m/s for oxygen (O2), respectively. The experimental results indicate that the flame stabilization of non-premixed oxy-methane flames decreased with increases in the CO2 mole fraction in the oxidizer. The flame spectra of non-premixed oxy-methane flames had a maximum intensity at the wavelength (λ) of λ=308nm. The reaction zone of non-premixed oxy-methane flames was broadened by the addition of CO2 to the oxidizer.

Evolution of the turbulent/non-turbulent interface of an axisymmetric turbulent jet

Measurements of a turbulent round air jet, using particle image velocimetry, were made to investigate the dynamics and transport processes at the continuous bounding interface between the turbulent and non-turbulent regions (T/NT) of the jet flow. The Reynolds number of the jet was in the range Re d = 3,000–6,500 based on jet diameter with measurements taken between 0 and 40 jet diameters from the jet nozzle exit, which covers the developing and self-similar region of the jet. A velocity thresholding technique was used to define the T/NT interface. The results based on this methodology were found to agree well with previously published results (Westerweel et al. in Phys Rev Lett 95:174501, 2005; Westerweel et al. in J Fluid Mech 631:199–230, 2009; and Anand and Boersma in Exp Fluids 47:995–1007, 2009). The evolution of the turbulence characteristics at the interface was investigated using conditionally averaged axial velocity, azimuthal vorticity, turbulent intensity, and Reynolds shear stress. A distinct change in behavior is observed between the near-field region, 0 ≤ x/d ≤ 8, and the far-field, self-similar region, x/d > 20. Profiles of the conditional mean axial velocity demonstrate no clear jump in the conditional mean axial velocity at the interface for x/d 20. All the scaled statistics show self-similar behavior downstream of x/d > 20. Similar behavior is observed for the peak in the azimuthal vorticity and the jump in the Reynolds shear stress profiles. The evolution of the rate of entrainment also confirms the creation and growth of the jump in the mean conditional velocity profiles in the developing region of the jet.