Exit Diameter Research Articles

Influence of nozzle geometry on wall static pressure coefficient of the submerged turbulent jet impinging on a smooth flat surface

The experimental work is carried out to study the influence of nozzle geometry on the flow characteristics of the submerged turbulent jet impinging on a smooth flat surface. Three nozzle geometry configurations, viz. parabolic, conical and exponential, are considered. Depending upon the nozzle exit diameter, the Reynolds number of 12,000–23,500 and jet-to-plate distance of 0.5–6 is considered. At a higher jet-to-plate distance (z/d = 6), a secondary peak was observed at a radial distance around r/d = 0.4 from the stagnation point. It is due to the transition of fluid flow from laminar to turbulent on the impingement surface. At all Re and z/d, parabolic nozzle geometry resulted in maximum value as compared with other nozzle geometry configurations. This may be attributed to higher pressure losses in the conical nozzle and exponential nozzle than the parabola nozzle because of streamlined flow and this information can be used for local heat transfer phenomena for optimum conditions.

Numerical study of a plasma jet for plasma-assisted laser cutting

Laser fusion cutting commonly applies a high-pressurized nitrogen gas jet to blow the molten material out of the cut kerf. However, theoretical considerations suggest that the use of a plasma jet may offer some advantages over this conventional approach. In this preliminary investigation, the characteristics of a non-transferred plasma jet for the application as auxiliary gas in laser beam cutting are analyzed using numerical CFD simulation. Based on this study, a first prototype of a plasma jet generator was manufactured and used in initial cutting experiments on 6 mm thick AISI 304 stainless steel. Two different cooling concepts for the plasma torch were considered and investigated in practice. Suitable values for the nozzle exit diameter, the distance between the electrodes of the plasma torch, the auxiliary gas flow rate and the electric current were identified both model-based and experimentally. The achieved cutting performance is considered a proof-of-principle of the suggested approach of a plasma-assisted laser beam cutting process.

Jet Flow and Noise Predictions for the Doak Laboratory Experiment

Large-eddy simulations (LESs) are performed for two isolated unheated jet flows corresponding to a Doak Laboratory experiment performed at the University of Southampton. The jet speeds studied correspond to acoustic Mach numbers of 0.6 and 0.8 as well as Reynolds numbers based on the nozzle exit diameter of about one million. The LES method is based on the compact accurately boundary-adjusting high-resolution technique (CABARET) and is implemented on graphics processing units (GPUs) to obtain 1000–1100 convective time units for statistical averaging with reasonable run times. In comparison with the previous jet LES calculations with the GPU CABARET method, the mean-flow velocity and turbulent intensity profiles are matched with the hot-wire measurements just downstream of the nozzle exit. The far-field noise spectra of the Doak jets are evaluated using two methods: the Ffowcs Williams–Hawkings approach and a reduced-order implementation of the Goldstein generalized acoustic analogy. The flow and noise results are compared with hot-wire and acoustic microphone measurements of the Doak Laboratory and critically analyzed in comparison with the NASA small hot jet acoustic rig database.

Updated frequency-dependent directivity indices for large solid rocket motors

For many years, empirical models for rocket noise radiation relied on the directivity indices published in NASA SP-8072 (K. Eldred, 1971). Because these indices had known issues, NASA led a campaign to update the indices using a Space Shuttle reusable solid rocket motor (RSRM). The RSRM measurements, involving a polar arc at a radius of about 80 nozzle exit diameters, resulted in updated directivity indices (Haynes and Kenny, AIAA 2009–3160). However, because the arc origin was placed at the nozzle exit plane, James et al. [Proc. Mtgs. Acoust., 18, 040008 (2012)] corrected the low-frequency indices using an estimated dominant source position for each frequency and assumed spherical spreading. This paper revisits that correction effort by using near-field vector intensity measurements from a similar, but smaller diameter and lower thrust, GEM-60 motor to determine the frequency-dependent origin to adjust the apparent angles and distances of the measurements. Additionally, an effort is made to account for RSRM plume impingement downstream that likely resulted in lower high-frequency levels than would have been measured if the plume had been entirely free. This analysis results in updated, frequency-dependent directivity indices for a large solid rocket motor. Their applicability to other rockets will be discussed.

Effect of tabs on the shear layer dynamics of a jet in cross-flow

Direct numerical simulations (DNS) of a jet in cross-flow (JICF) with a triangular tab at two positions are performed at jet-to-cross-flow velocity ratios of $R = 2$ and $4$ with a jet Reynolds number of 2000 based on the jet's bulk velocity and exit diameter. The DNS and dynamic mode decomposition show the sensitivity of the tab's effect on the jet upstream shear layer (USL) structure and cross-section to $R$ , echoing the experimental discoveries of Harris et al. (J. Fluid Mech., vol. 918, 2021). Furthermore, DNS reveals that the presence of a tab placed on the upstream side of the nozzle significantly modifies the USL through production of streamwise vortices that curl around the spanwise vortex tubes originating from the primary instability of the USL. This provides an explanation for the improvement in mixing that has been associated with an upstream tab. The streamwise vortex structure shows remarkable similarities to the ‘strain-oriented vortex tubes’ observed for disturbed plane shear layers by Lasheras & Choi (J. Fluid Mech., vol. 189, 1988, pp. 53–86). For both $R$ cases, the USL instability is delayed, the jet penetration is reduced, and the jet cross-section is flattened, although the tab has a less pronounced effect on the USL structure at higher velocity ratios, where the formation of the streamwise vortices is delayed. In contrast, a tab placed 45 $^\circ$ from the upstream position produces significantly different effects compared with the upstream tab. At $R = 4$ , the jet cross-section is significantly skewed away from the tab and a tertiary vortex is formed, as observed in past studies of round JICFs at relatively high $R$ and low Reynolds numbers. The ability of the tab to produce a controllable steady-state tertiary vortex has implications for a variety of applications. The 45 $^\circ$ tab produces asymmetric effects in the wake of the jet at $R = 2$ , but the effect on the jet cross-section is much smaller, highlighting the sensitivity of jets at high $R$ to asymmetric perturbations.

Hole diameter variation compensation by integrating computation geometry for helical milling of stacked aerostructure

The stack-ups of composite and metal are used in aircraft manufacturing to produce modern high-performance aircraft, which makes fastener-hole-making more difficult. Helical milling is an advanced machining process to improve the quality of hole-making. This paper seeks to control the hole diameter error and guarantee fastener-hole fitting performance. The setup of automated helical milling for assembling composite/metal aerostructures is first presented. Meanwhile, the helical milling procedure in aircraft wing manufacturing is discussed. Based on the designed helical milling end-effector, a length-gauge-based feedback control mechanism of the orbital eccentricity is designed to reduce the diameter error of an intended fastener hole. For accurate measurement, a least-squares method is used to find the calibration parameters of the length gauge. Then the mathematical model of hole diameter variation extraction based on B-spline curve construction is given for further variation compensation. After that, the feedback control system of the radial feed mechanism is established. Besides, the modeling and compensation system of the hole diameter variation is developed and used. In helical milling of CFRP/Ti stacks in an aircraft assembly, fastener holes tend to achieve the target diameter of 7.9400 mm without extending the range of hole entrance and exit diameters.

Experimental study of hydrocarbon aviation fuel jets at high temperatures up to the critical point

An experimental study was conducted to investigate the effects of fuel temperature up to the critical point on the injection and hydrodynamic characteristics of practical hydrocarbon aviation fuel jets. Pressurized heated hydrocarbon, simulating aviation fuel used as coolant in the active cooling system of a hypersonic flight vehicle, was injected through a set of plain orifice nozzles of exit diameters 0.7 and 1.0 mm. The fuel was heated to close to 700 K (427 °C) using an induction heater, and discharged to atmospheric pressure and temperature conditions. Visual observation of the fuel spray and the shock structure near the nozzle exit shows that morphological change is drastic in the temperature range between the boiling point and the critical temperature; this allows delineation of the liquid, flash boiling, and near-critical regimes. An in-depth investigation of the near-critical regime through shadowgraph images reveals that the structure of the hydrocarbon fuel jets near the critical temperature looks very similar to that of typical underexpanded jets. Furthermore, visual observation confirms that the distance hs from the nozzle exit to the shock structures is correlated with the injection pressure ΔP irrespective of the fuel injection temperature Tinj. Hydraulic characterization by measuring ΔP and the resultant discharge coefficient Cd with respect to Tinj under fixed mass flow rates shows that Cd is almost constant in the liquid regime, while it decreases with Tinj in the flash boiling regime, and that a discontinuity near the boiling point occurs where the liquid injection transitions to flash boiling. A simple linear model is proposed to estimate the P-T relation in the flash boiling regime by linearly extending the characteristics of the hydraulic performance.

Acoustic resonance mechanism for axisymmetric screech modes of underexpanded jets impinging on an inclined plate

In this paper, the acoustic resonance mechanism for different axisymmetric screech modes of the underexpanded jets that impinge on an inclined plate is investigated experimentally. The ideally expanded Mach number of jets ( $M_j$ ) ranges from 1.05 to 1.56. The nozzle-to-plate distance at the jet axis and the impingement angle are respectively set as 5.0 $D$ and $30^{\circ }$ , where $D$ is the nozzle exit diameter. The acoustic results show that the $M_j$ range for the A2 screech mode of impinging jets is broader than that of underexpanded free jets, and a new axisymmetric screech mode A3 appears. With the increase of $M_j$ , the effect of the impinging plate on the shock cell structures of jets becomes obvious gradually, and the second suboptimal peaks are evident in the axial wavenumber spectra of mean shock structures. The coherent flow structures at screech frequencies are extracted from time-resolved schlieren images via the spectral proper orthogonal decomposition (SPOD). The axial wavenumber spectra of the selected SPOD modes suggest that the A1, A2 and A3 screech modes are respectively closed by the guided jet modes that are energized by the interactions between the Kelvin–Helmholtz wavepacket and the first three shock wavenumber peaks. The upstream- and downstream-propagating waves that constitute the screech feedback loop are analysed by applying wavenumber filters to the wavenumber spectra of SPOD modes. The frequencies of these three screech modes can be predicted by the phase constraints between the nozzle exit and the rear edge of the third shock cell. For the A3 mode, the inclined plate invades the third shock cell with the increase of $M_j$ , and the phase constraint cannot be satisfied at the lower side of the jets, which leads the A3 mode to fade away. The present results suggest that external boundaries can modulate the frequency and mode of jet screech by changing the axial spacings of shock cells.

Influence of Exposure Parameters on Nanoliquid-Assisted Glass Drilling Process Using CO2 Laser

Liquid-assisted laser processing (LALP) is implemented using a 10.6 μm continuous-wave (CW) CO2 laser to drill holes in 1.1 mm thick soda-lime glass substrates fully immersed in a nanoliquid bath. The nanoliquid bath consisted of de-ionized water and carbon nano-particles (CNPs) of different wt.%. The study focuses on the influence of exposure time (TE, [s]), laser beam power (P, [W]) and number of pulses (NP) on resulting geometrical features, namely, crack length (CL, [mm]), inlet diameter (DINLET, [mm]) and exit diameter (DEXIT, [mm]). The processed samples were characterized using an optical microscope. Findings show that LALP with investigated ranges of control parameters TE (0.5–1.5 s), P (20–40 W) and NP (1–6 pulses) led to successful production of drilled holes having CL range (0.141 to 0.428 mm), DINLET range (0.406 to 1.452 mm) and DEXIT range (0.247 to 1.039 mm). It was concluded that increasing TE alone leads to increasing CL, DINLET and DEXIT, while keeping a good balance among the control parameters, especially TE and NP, will result in reduced CL values. Moreover, process statistical models were developed using statistical analysis of variance (ANOVA). These models can be used to further understand and control the process within the investigated ranges of control and response parameters.

Design of a single glass tube optical lens for soft X-ray laser decoherence

Laser has the advantages of high brightness, good monochromaticity, high coherence and good directionality, however, in some cases such as laser imaging and laser processing where only its high brightness or high monochromaticity is desired, the interference effect caused by high coherence can affect and limit its effective applications. In this work, a new single glass tube decoherence lens (SGTDL) is designed for soft X-ray laser decoherence through the simulation calculations. The simulation results show that an SGTDL with an entrance diameter of 5 mm, exit diameter of 0.6 mm and a length of 15 cm can effectively reduce the coherence of the X-ray laser with a wavelength of 10 nm and a beam waist radius of 1.25 mm. At the same time, the exit beam with a divergence range of 30–50 mrad is obtained at the SGTDL’s exit, and the transmission efficiency and gain in power density of the SGTDL are 78% and 52.74, respectively. For a laser beam with a wavelength of up to 1 nm, this model of SGTDL can maintain the transmission efficiency of the beam at more than 30%. This work also discusses the influence of the X-ray laser energy and the SGTDL’s length on the transmission performances of the SGTDL. The results show that the SGTDL designed according to the total reflection principle can meet the application requirements for laser decoherence in a range from the extreme ultraviolet to X-ray wavelength, and has a wide application prospect in X-ray laser imaging, laser processing, etc.

Study of Steam-Induced Convection in a Rotating Vertical Flow Channel

The phenomenon of steam–water direct contact condensation has significance in a wide range of industrial applications. Superheated steam was injected upward into a cylindrical water vessel. Visual observations were conducted on a turbulent steam jet to determine the dimensionless steam jet length compared to the steam nozzle exit diameter and the steam maximum swelling ratio as a function of steam mass flux at the nozzle exit, with a gas steam flux ranging from 295–883 kg/m2s. The Reynolds number based on the steam jet’s maximum expansion ranged from 41,000 to 93,000. Farther above of the condensation region, the jet evolved as a single-phase heated plume, surrounded by ambient water. Mean axial central velocity profiles were determined against the steam mass flux ranging from 295–883 kg/m2s to observe the exponential drop in the mean axial velocity as the vertical distance increased. The radial velocity distribution within the spread of the jet was determined to be self-similar, and the radial distribution of the velocity profile followed the Gaussian function, after the proper scaling of the vertical distance and the axial mean velocity.

A Study on the Erosion Mechanism of an Axial Cyclone Separator for Gas Purification

Severe erosion occurs in the cone bottom and the joint part between the cone and cylinder of the cyclone separator used in high-pressure natural gas transportation. The main objective of this study is to reveal the mechanism and influencing factors of erosion. To address these issues, the numerical simulations were used to investigate the parameters, such as inlet gas velocity, particle concentration, particle size, the cone length, the diameter of dust exit and the vortex finder. The results indicate that wall erosion is significantly affected by the inlet gas velocity and particle diameter. Increasing the cone length and the dust exit diameter can effectively reduce wall erosion, whereas the cyclone separation efficiency would be reduced simultaneously. It is worth noting that the vortex finder with spiral slits is of benefit to increase the cyclone separation efficiency but decreases the maximum erosion rate of the cyclone cone by at least 80%.

Effect of bypass ratio on sonic underexpanded co-flow jets with finite lip thickness

Abstract The characteristics of a sonic under-expanded coaxial jet with lip thickness 1.5D p (where D p is the exit diameter of primary jet equals 10 mm) with the primary jet operating at nozzle pressure ratio (NPR) of 3, 4 and 5. For NPR 3 operating primary jet, the secondary jet operates at NPR 2.5, 1.4 and 1.27. For primary jet NPR 4, the secondary jet operating NPR is 3.2, 1.6 and 1.4. For NPR 5 primary jet, the secondary jet NPR is 3.8, 1.89 and 1.52. The study is performed using a co-flow nozzle of bypass ratio (BR) 6.4, 1.4 and 0.7. The core length of the primary jet is used as a measure to quantify the mixing of the primary jet in the presence of coaxial jet. The shock structure present in the near field was viewed using shadowgraph technique. Centreline pitot pressure distribution, radial spread and waves present in the jet core were analyzed. The results show that the mixing associated with the high bypass coaxial jet is superior to the low bypass coaxial jet. This mixing superiority associated with high bypass coaxial jet prevails all levels of expansion.

Quantitative criteria for designing thrust gates to mitigate jet-flap interaction noise

Thrust gates have been reported as a promising concept to reduce jet-flap interaction noise. This manuscript proposes two quantitative criteria for the design of thrust gates based on time-averaged flow parameters that can be extracted from steady-state simulations. Computations were carried out by solving the explicit, transient, compressible lattice Boltzmann equation, while the acoustic far-field was obtained via the Ffowcs-Williams and Hawkings analogy. After being validated based on the truncation error and comparisons with measurements for the far-field acoustics, the simulation model was used in a parametric analysis of thrust gates, varying the width (W/DJ = 1,2,3,4) for a fixed depth B/CF = 1, where DJ is the nozzle exit diameter and CF is the flap chord. Also, two acoustic Mach numbers (Ma = 0.5 and Ma = 0.7) and two flap deflection angles (α = 7° and α = 30°) were considered. The results show that thrust gates with W/DJ > 1 and W/DJ > 2 do not reduce significantly the far-field noise in weak (α = 7°) and strong (α = 30°) jet-flap interaction configurations for both Mach numbers. In this context, the jet-spreading angle and pressure-load are proposed as criteria for designing thrust gates that are effective for noise reduction but with minimum cutout on the flap. Thrust gates designed according to the pressure-load criterion were quieter by around 0.89 dB (α = 7°) and 4.25 dB (α = 30°) for Ma = 0.5, and 0.94 dB (α = 7°) and 3.53 dB (α = 30°) for Ma = 0.7 in comparison with those designed following the jet-spreading criterion. Additionally, the pressure-load criterion was also shown to be effective in reducing the cutout on the flap.

Large-Eddy Simulation of a Water Jet Exhausting into Quiescent Air

This study focuses on a water injection system, typical of those used to inject water in the motor jet plume of rocket engines to reduce noise, and particularly on the destabilization of the liquid jet that leads to a spray system. For that purpose, a large-eddy simulation is conducted for an experimental water jet of the literature. It is a sprinkler whose Reynolds number is and nozzle exit diameter is , similar to injectors used for jet noise reduction studies at a reduced scale. A diffuse interface method is used to calculate the dense liquid phase, and the dispersed phase containing droplets is calculated with an Eulerian solver. Transfers between the dense and the dispersed phases are modeled in the coupling procedure, including the atomization and impingement processes. The jet mean radius and initial instability frequency are consistent with the experimental data, while the position of the jet transition varies with the fluctuation levels at the nozzle exit. The droplets are created in the shear layer and accumulate on the jet center when only the atomization process is considered. When also implemented, the impingement phenomenon, however, is shown to absorb the droplets before they reach the center.

Effect of Water Injection on Turbine Inlet under Different Flight Conditions

Numerical simulations were conducted to research the pre-cooling effects of water injection on the turbine inlet of a turbine-based combined cycle (TBCC) engine under different flight conditions. Then, the performance of the water injection pre-compressor cooling (WIPCC) engine was calculated by mathematical modelling with different water to air ratios (WAR). It was the first time that the mass injection field of the turbine inlet of a TBCC engine was simulated, and it was also the first time that the performance of a subcomponent turbine engine of a TBCC was assessed. The calculation results showed the relationship of the inlet temperature with respect to WAR, inlet length and flight Mach number. The strategy for inlet length and water mass flow was proposed in order to meet the requirements of pre-cooling. When the length of the turbine inlet was 10 times the diameter of the inlet exit, the air could be cooled by 167.5 K with WAR = 0.09. The highest evaporation ratio reached at 93%. Finally, the calculation results revealed the performance of the water-pre-cooled turbine engine, of which the flight envelope was expanded to Ma3.0 from Ma2.3 by pre-cooling. The engine thrust as well as the specific impulse were significantly improved. The thrust reached at 0.9 times the characteristic thrust meeting the TBCC mode transition requirement of thrust and working speed spectrum.

Aerodynamic Characteristics of a Ducted Fan Hovering and Transition in Ground Effect

Ducted fans installed on vertical takeoff and landing vehicles experience significant ground effect during takeoff and landing. The aerodynamic characteristics of a ducted fan hovering and transitioning in the ground effect are studied using numerical simulations in this paper. The flowfields are obtained by solving Reynolds Averaged Navier–Stokes equations with the Multiple Reference Frame approach. When a ducted fan hovers in the ground effect, the blade thrust increases due to the combined effect of the increase in the effective angle of attack of the blade and the increase in ambient pressure; the duct thrust decreases due to the combined effect of the decrease in the effective angle of attack of the duct and the increase in ambient pressure. Stall occurs at a certain advance ratio and angle of attack when transitioning in the ground effect. The ground effect delays the occurrence of stall at some advance ratios. The ground effect is hardly detectable at angles of attack less than 30° even if the height drops to 0.5 times the duct exit diameter. At this height and high angles of attack, the different positions and influence regions of the ground vortex at different advance ratios contribute to the different variation trends in the ducted fan performance.

Analysis of Gas Flow Dynamics in Thermal Cut Kerf Using a Numerical and Experimental Approach for Nozzle Selection

Consistency in gas flow behavior under various operating conditions is expected for uniform cutting performance in the thermal cutting process. The slope of the cut front in the kerf slot of a sample cutting material varies with the operating condition which affects the gas flow pattern. Therefore, how the nozzle exit diameter and the slope of the cut front effects gas flow behavior has been studied using the Reynolds averaged Navier–Stokes (RANS) based k–ω turbulence model. Convergent–straight-type nozzles with exit diameters φexit of 1.5 mm, 2 mm and 2.5 mm were used to study the flow patterns through the kerf slots of variable cut front slopes. The numerical simulation results were then compared with the results obtained from the Schlieren experiments. In addition, image processing was performed in the Schlieren images for clear visualization and precise comparison of the numerical and experimental data. The results confirm that a nozzle with an exit diameter of 2 mm shows a higher consistency in flow behavior in variable operating conditions.

Micro-drilling of alkali-silicate glass with ultraviolet picosecond laser

The low efficiency of UV-laser ablation of transparent alkali-silicate glass has been increased by means of irradiation by 60Co γ-quanta to doses 104 −107 Gy to induce intensive UV-visible coloration. Varying the picosecond pulse energy of Nd:YAG laser at 4-harmonics 266 nm within 1−9 mJ and pulse number, arrays and grids of holes were drilled with diameters from 9 to 40 µm on area up to 1×1 cm2 . Shock waves of 4−5 µm were generated by expanding plasma around ablated holes at focused pulse energy density >108 J/m2 and nanoscale crystallization occurred there. Besides, a submicron hole was drilled aside the central micron hole due to generation of vacuum UV harmonics. The combined effect of γ-irradiation followed by UV laser drilling has resulted in decrease of silicon and oxygen contents, and generation of fluorine that may be caused by photonuclear reactions 28Si14→19F9+ 33Т1; 16O8→44He2; 16О8+3Т1→19F9. Because of glass viscosity and relaxation during 2 months at 300 K, the exit diameter of drilled holes has increased up to the entry one. Such micro-scale grids can be used for separating liquid mixtures or cleaning water.

On Flame Extinction and Free-Floating Limits Using a Large Diameter Opposed Jet Burner

ABSTRACT This paper presents studies on flame extinction and associated flame structure using a large diameter (40 mm) opposed jet burner for the first time. The extinction experiments were carried out at various nozzle separation distance (L) to diameter (D) ratios (L/Ds) for methane-air non-premixed flames, while all similar experiments in the past literature are with smaller burner diameters (<25 mm). The extinction studies were used to determine the free-floating limits of the burner, and a detailed analysis of the effect of nozzle exit diameter and Applied Stress Rates (ASRs) on the free-floating limits are reported by comparing with similar works in the past. The Particle Image Velocimetry (PIV) technique was used to determine the axial velocity profiles and local extinction strain rates (Kl) of the flames. Based on the experiments, a correlation for the free-floating separation distance from the stagnation plane (zFF) is proposed, which was found to be proportional to the square of the ASRs. The reported free-floating limits in the literature using various diameters agree with the observed data trend. This solves the ambiguity regarding the free-floating limits of opposed jet burners and provides a general trend of the free-floating separation distance (LFF) even in the off-extinction operation regime. 2D axisymmetric simulations were carried out using realistic boundary conditions on the OpenFOAM® platform to predict flame extinction and, consequently, global flame extinction strain rates (Kg). The model predicts the Kg values and also its trend with L/Ds accurately. The model also captures the flame structure before extinction for various L/Ds.