Nozzle Exit Diameter Research Articles

Influence of Nozzle Exit Conditions on the Near-Field Development of High Subsonic and Underexpanded Axisymmetric Jets

Detailed knowledge of jet plume development in the near-field (the first 10–15 nozzle exit diameters for a round jet) is important in aero-engine propulsion system design, e.g., for jet noise and plume infrared (IR) signature assessment. Nozzle exit Mach numbers are often high subsonic but improperly expanded (e.g., shock-containing) plumes also occur; high Reynolds numbers (O (106)) are typical. The near-field is obviously influenced by nozzle exit conditions (velocity/turbulence profiles) so knowledge of exit boundary layer characteristics is desirable. Therefore, an experimental study was carried out to provide detailed data on nozzle inlet and exit conditions and near-field development for convergent round nozzles operated at Nozzle Pressure Ratios (NPRs) corresponding to high subsonic and supersonic (underexpanded) jet plumes. Both pneumatic probe and Laser Doppler Anemometry (LDA) measurements were made. The data revealed that internal nozzle acceleration led to a dramatic reduction in wall boundary layer thickness and a more laminar-like profile shape. The addition of a parallel wall extension to the end of the nozzle allowed the boundary layer to return to a turbulent state, increasing its thickness, and removing vena contracta effects. Differences in nozzle exit boundary layers exerted a noticeable influence but only in the first few diameters of plume development. The addition of the exit extension removed the vena contracta effects of the convergence only design. At underexpanded NPRs, this change to nozzle geometry modified the shock cell pattern and shortened the potential core length of the jet.

NUMERICAL INVESTIGATION ON THE INTERACTION OF A PAIR OF HOT OFF-DESIGN SUPERSONIC JETS WITH A JET BLAST DEFLECTOR

The interaction of a pair of hot off-design jets from biconical supersonic nozzles is numerically investigated by the high-resolution RANS/ILES method. The distance between the jet axes is four nozzle exit diameters. To improve the computational accuracy, combined computations of the flows in the nozzles and in the jets escaping from these nozzles are performed. The computations are carried out for free jets with a co-flow and for airfield jets with a jet blast deflector. Distances where mixing layers interaction begins, where jets are merging and where the difference of flow characteristic between one jet and twin jets are observed were obtained. The influence of the pair of jets on the near acoustic field is considered. For airfield jets, the effects of the co-flow velocity and the distance from the nozzle exit to the jet deflector on the size and shape of dangerous areas in terms of temperature, pressure fluctuations, and axial velocity are detected. Generalizing dependencies are presented for evaluating the influence of these parameters on the typical sizes of the dangerous zones. The results of the simulations are compared with similar data for single jet impingement onto the jet deflector. Specific features of the effects of the co-flow velocity and the jet deflector position on pressure, temperature, and their fluctuations over the jet blast deflector height are found.

CFD Analysis of CD Nozzle and Effect of Nozzle Pressure Ratio on Pressure and Velocity for Suddenly Expanded Flows

A numerical work was carried out to study the effectiveness of micro-jets to control base pressure in suddenly expanded two-dimensional planar duct. Two micro-jets of 1 mm orifice diameter located at 90° intervals along a pitch circle distance of 1.5 times the nozzle exit diameter in the base region were employed as active controls. The calibrated Mach numbers at the entry to suddenly expanded duct was 1.87. The length-to-diameter ratio (L/D) of suddenly expanded duct was 10. Nozzles generating the calibrated Mach numbers were operated with nozzle pressure ratio (NPR) 3, 5, 7, 9 and 11. From the present investigation it is evident that for a given Mach number and effect of NPR will result in maximum increase/decrease of pressure and velocity. The convergent-divergent nozzle geometry has been modeled and simulated employing turbulence models: K-e standard wall function turbulence model from the code was independently checked with the commercial computational fluid dynamics.

Effect of standoff distance and area ratio on the performance of circular exhaust ejector using computational fluid dynamics

Numerical investigation is carried out to study the effect of standoff distance and area ratio on mass entrainment of an air–air circular exhaust ejector. Nozzle and mixing tube are the two components of an ejector, and for the present study, circular cross section shape has been chosen. Numerical simulations have been carried out at Reynolds number in the range of 6.85 × 104 and 4.11 × 105. Area ratio is varied between 1.25 < area ratio < 4 and standoff distance is varied from 1 Dnz < standoff distance < 4 Dnz, where Dnz represent the nozzle exit diameter. It is observed that for the ejector configuration with area ratio as 2, 2.25, and 2.5, the mass entrainment characteristics are nearly independent of standoff distance between 1 Dnz to 4 Dnz. For ejector configuration with area ratio below 2, mass entrainment decreases with increase in standoff distance. For ejector configuration with area ratio greater than 2.5, mass entrainment increases with increase in standoff distance for the range investigated and has the tendency to taper off beyond 4 Dnz for most of the area ratios. Effect of change in mixing tube length is also studied. It is seen that the mass entrainment improves with increase in length up to 8 Dnz. Further increase in length does not effect mass entrainment. This study provides important guidelines that can aid in arriving at an optimal design of circular exhaust ejectors.

Condition Monitoring of Focusing Nozzle in Abrasive Water Jet Machine using Sound Sensor

Objectives: The condition monitoring was done during the machining of Stainless Steel 316 Grade using a PCB microphone with a view to related the measured Sound Signal with the nozzle wear obtained. Methods/Statistical Analysis: It is done by using a Data Acquisition Device is used to connect the Computer with the microphone to analyze the signal using LAB VIEW Software. Also a Sensor signal conditioner is attached to the microphone to boost the sound signal. The machining is done by changing the abrasive flow rate and pressure parameters and the corresponding sound signal is recorded Findings: Regression analysis was carried out using Minitab 17 software and results showed that abrasive flow rate has more influence on nozzle wear rate. Regression equations were also developed for each nozzle hour based on process parameters. Also it was observed that the nozzle exit diameter increases with increase in nozzle life time. Application/Improvements: The future aspects are to develop a generalized equation for the nozzle wear rate based on the process parameters to develop a closed loop system.

Aerodynamic force and moment measurement of 10° half-angle cone in JF12 shock tunnel

An aerodynamic force and moment measurement was conducted in JF12 long-test-duration detonation-driven shock tunnel of Institute of Mechanics, Chinese Academy of Sciences. The test duration of JF12 is 100–130ms. The nominal Mach number is 7.0 and the exit diameter of the contoured nozzle is 2.5m. The total enthalpy is 2.5MJ/kg which duplicates the hypersonic flight conditions of Mach number 7.0 at 35km altitude. The test model is the standard aerodynamic force model of 10° half-angle sharp cone. The length of the test model is 1500mm and the weight is 57kg. The aerodynamic forces were measured with a six-component strain balance. The angles of attack were set to be −5°, 0°, 5°, 10° and 14°, respectively. The experimental results show that in the 100–130ms test duration, the signals of strain balance have 3–4 complete vibration cycles. So, the aerodynamic forces and moments can be obtained directly by averaging the signals of balance without acceleration compensation. The force measurement error of repeatability of JF12 is less than 2%. The aerodynamic force coefficients of JF12 are in good agreement with those of conventional hypersonic wind tunnels. For this test model at Mach number 7.0 and total enthalpy of 2.5MJ/kg, the real-gas effects on aerodynamic force characteristics are not very evident.

Broad band shock associated noise predictions in axisymmetric and asymmetric jets using an improved turbulence scale model

Supersonic jets that are subject to off-design operating conditions are marked by three distinct regions in their far-field spectra: mixing noise, screech and Broadband Shock Associated Noise (BBSAN). BBSAN is conspicuous by the prominent multiple peaks. The Morris and Miller BBSAN model that is based on an acoustic analogy, offering a straightforward implementation for RANS, forms the foundation of the present work. The analogy model robustly captures the peak frequency noise, that occurs near Strouhal number of about 1, based on the nozzle exit diameter but leads to major sound under prediction for higher frequencies. In the jet mixing noise literature, it has been shown that an inclusion of frequency dependence into the characteristic length and temporal scales of the effective noise sources improves the far-field noise predictions. In the present paper, several modifications of the original Morris and Miller model are considered that incorporate the frequency dependent scales as recommended in the jet mixing noise literature. In addition to these, a new mixed scale model is proposed that incorporates a correlation scale that depends both on the mean-flow velocity gradient and the standard mixing noise-type scaling based on the dissipation of turbulent kinetic energy. In comparison with the original Morris and Miller model, the mixed scale model shows considerable improvements in the noise predictions for the benchmark axisymmetric convergent-divergent and convergent jets. Further to this validation, the new model has been applied for improved predictions for elliptic jets of various eccentricity. It has been shown that, for the same thrust conditions, the elliptical nozzles lead to noise reduction at the source in comparison with the baseline axisymmetric jets.

Control of Ideally Expanded and under Expanded Nozzle Flows with Micro Jets

This paper presents an experimental investigation of an airflow from convergent-divergent axisymmetric nozzles expanded suddenly into circular duct of larger cross-sectional area than that of nozzle exit area, focusing attention on the base pressure and the flow development in the duct. To investigate the influence of active control on wall pressure as well as on the flow field developed in the duct, the micro jets of 1 mm orifice diameter located at 900 interval along a pitch circle diameter 1.3 times the nozzle exit diameter were employed as the controller of the base pressure. The Mach number investigated in the present study was 1.30. The area ratio of the present study was 2.56. The nozzle pressure ratio (NPR) used were from 2.77 and 4.16 respectively which corresponds to correct and under expanded conditions. The length-to-diameter ratio of the enlarged duct was varied from 10 to 1.The level of expansion at the nozzle exit (i.e. before sudden expansion) influences the wall pressure very strongly. When the micro jets were activated they found to influence the flow in the enlarged duct. Wall pressure results for correctly expanded and under expended jets indicate that the flow in the enlarged duct remains attached for L/Ds including at L/D =1. Also, it is found that the wall pressure flow field in the duct for with and without control are identical and the control in the form of the micro jets does disturb the flow field. Results for L/D = 8 and 10 for correctly expanded jets indicate peculiar phenomenon and are totally different from all the results for lower L/Ds. Wall pressure results for under expanded jets indicate that control results in marginal decrease in the wall pressure otherwise the wall pressure flow field with and without control remains same.

Exploring Physics and Control of Twin Supersonic Circular Jets

The closely spaced twin-jet configuration often seen in military aircraft is distinct from the single jet in both the flowfield and acoustic field. The twin-jet plumes interact with each other weakly or strongly, depending upon the distance between the two jets, the jet operating flow regime, and the Mach number. In the current study, the interaction mechanisms and coupling of a supersonic twin jet exhausting from biconical converging–diverging nozzles with a design Mach number of 1.23 at a separation distance of two nozzle exit diameters are investigated using near-field pressure measurements and phase-locked flow visualization. Across a series of jet operating Mach numbers, the twin-jet plumes feature three major jet azimuthal modes: axisymmetric, helical, and flapping. The jet flapping mode is strongly augmented in the twin-jet configuration compared to the single-jet case. Along the twin-jet plane, which is also the plane of the jet flapping direction, jet plumes with coherent flow structures are observed to move up and down. Because of the nature of the jet flapping motion, the near-field pressure fluctuations are markedly amplified at low Strouhal numbers, particularly along the twin-jet plane for further downstream locations where the coherent structures are developed and large. Localized arc filament plasma actuators are implemented as an active flow control tool on both nozzles, just upstream of nozzle exit, to explore the coupling mechanisms. The results show that decoupling and coupling of twin-jet plumes can both be achieved, depending on the jet operating condition and the excitation parameters employed.

An experimental analysis of the impact of primary nozzle geometries on the ejector performance used in R141b ejector refrigerator

This paper gives an experimental discussion of the geometrical impact of the primary nozzle on the ejector performance in an R141b ejector refrigerator. Primary nozzle area ratio is varied to observe its effect on the ejector performance. Six primary nozzles are investigated experimentally. Four of them (D2.4M2.5, D2.8M2.5, D3.2M2.5, and D3.6M2.5) are designed with different throat diameters, but they have an identical nozzle area ratio. Two of them, D2.4M2.0 and D2.4M3.0, have an identical throat diameter, but they have different nozzle area ratio, resulting in a different nozzle exit Mach number. All nozzles are tested with one fixed geometry ejector at various operating conditions. Variations of the primary momentum caused by the change in primary nozzle throat and nozzle exit Mach number on the ejector performance is observed and discussed. The purpose is to determine the optimal primary nozzle geometries at given operating conditions. It is found that using a bigger nozzle throat, operated with lower generator temperature, is preferable. The primary nozzle exit Mach number should be as high as possible. It should also be designed to be consistent with the heat source’s temperature for implementing the nozzle at the designed conditions. The primary nozzle exit diameter must be consistent with the mixing chamber used. Therefore, the minimum required generator temperature (Tgen-min) at various nozzle exit Mach numbers and the largest possible nozzle exit diameter for one particular ejector are provided for this present work.

An analytical model for the prediction of temperature distribution and evolution in hybrid laser-waterjet micro-machining

A hybrid laser-waterjet micro-machining technology was developed for near damage-free micro-ablation recently. It uses a new material removal concept where the laser-softened material is expelled by a pressurised waterjet. The temperature field in this hybrid machining process is an essential quantity for understanding the underlying material removal mechanism and optimizing the process conditions. This study presents a three-dimensional (3-D) analytical model for the temperature field in this hybrid laser-waterjet micro-machining process. The interaction among the laser, waterjet, and workpiece is considered in the model. The absorption of laser by water, the formation of laser-induced plasma in water, the bubble formation and the laser refraction at the air-water interface are discussed. DuHamel’s principle is used to determine a closed-form temperature equation and a solution in a variable separation form is obtained. A calculation for silicon carbide is conducted. The results are illustrated by a group of 3-D temperature profiles intuitively and visually. It is shown that the temperatures are below the melting point during the process due to the cooling action of waterjet. The almost damage-free micro-machining can be achieved. Besides, the maximum temperature increases with the increased average laser power and waterjet offset distance and decreased nozzle exit diameter where the average laser power takes a major action.

On the Influence of Array Size and Jet Spacing on Jet Interactions and Confluence in Round Jet Arrays

This work uses computational models to study the effects of confluence and jet-to-jet interactions for inline matrices of confluent round jets. In total, 12 different confluent jet arrangements, having various jet array sizes and dimensionless jet spacing, S/d0, have been investigated. The array size varies from 6 × 6 to 10 × 10 jets, while S/d0 varies between 1.75≤S/d0≤4.0. The Reynolds number, based on the nozzle exit diameter, is between 2200 and 6600. The results show that both jet spacing and jet array size largely influence the jet-to-jet interactions and flow field development in confluent jet arrays. The jet interactions in the investigated setups result in regions of negative static pressure between jets, jet deformation, high spanwise velocity, and jet displacement. Generally, smaller jet spacing and larger array size result in stronger influence of jet interactions. After the jets have combined, the confluent jets form a zone with constant maximum streamwise velocity and decay of turbulence intensity, called a confluent core zone (CCZ). During the CCZ, the combined jet will have asymmetric spreading rates leading to axis-switching. The entrainment rate of the CCZ is constant, but the volumetric flow rate of the combined jet is substantially affected by the degree of entrainment before the jets have combined.

폴리우레탄 발포 노즐 형상이 혼합 성능에 미치는 영향

For reaction injection molding (RIM) polyurethane was mixed in the mixing head by impingement mixing, injected into the mold, and cured quickly, as soon as the mold is filled. The shape of the nozzle in the mixing head is critical to improve the quality of polyurethane. To achieve homogeneous mixing, an intensive turbulence energy in the mixing nozzle is essential. In this study, a mixing nozzle for RIM was designed, and mixing efficiency was investigated based on experiment. Experiments were conducted with different combinations of nozzle tips and exit diameter to measure the mixing efficiency by measuring jet force and investigating mixing image with high speed camera. Jet force increased gradually and reaches steady state conditions. The jet force depended on shape of nozzle tip and outlet sizes. These results suggest that optimized nozzle configurations are necessary for high efficiency mixing with RIM.

High dynamic range thermometry at 5 kHz in hydrogen–air diffusion flame using chirped‐probe‐pulse femtosecond coherent anti‐stokes Raman scattering

Chirped probe pulse femtosecond coherent anti‐Stokes Raman scattering (CPP fs‐CARS) thermometry was performed at 5 kHz in a hydrogen jet diffusion flame with an air co‐flow. Measurements were performed at different heights and radial locations within the jet diffusion flame, up to 16 nozzle exit diameters downstream (x/d = 16). The near‐nozzle measurements were characterized by large, organized, buoyancy‐driven instabilities that become more chaotic at the downstream locations x/d ≥ 4. The diffusion flame results highlight temperature fluctuations characteristic of the buoyancy‐driven Kelvin–Helmholtz‐type instability and provide new insights into the transient structure of these flames. At some measurement locations, the time‐varying temperatures ranged from 300 K to nearly 2400 K. The CPP fs‐CARS signal intensity is a factor of approximately 1000 times lower at 2400 K compared with 300 K. A dual‐channel detection system was used to increase the dynamic range of the CARS measurements. The determination of temperature from the single shot spectra is discussed in detail. Laser and detection system parameters were determined from CPP fs‐CARS spectra obtained from a near‐adiabatic laminar calibration flame apparatus. The temperature precision of the system was determined from these calibration measurements and was found to be better than 2.0% at 2200 K. The influence of an instrument response function on spectral fitting parameters is systematically assessed. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Adaptive air distribution in an ejector burner for the utilisation of methanol-mixed fuels

Numerous studies have focused on the utilisation of alcohol fuels because of the energy crisis. However, the combustion efficiency and stability of alcohol fuels are unacceptable. This study proposed an ejecting combustion method for utilising methanol-mixed fuels and numerically investigated the characteristics of adaptive air distribution in an ejector burner. The geometrical parameters of the ejector burner were optimised and validated by an experiment. Results show that the suction effect of negative pressure in the mixing chamber and the entrainment effect of fuel jet flow both play important roles for an ejector burner to draw air. The positions of ejector nozzle exit locating at the suction chamber axis and low operating pressure are beneficial for obtaining a stable air distribution. Molar entrainment ratio (MER) rapidly increases with an increase in parameter α, which is defined as the ratio of throat diameter to nozzle exit diameter, but declines with increasing ejector back pressure. In the experiment, the changing rate of MER is less than 6.4%, and combustion efficiency is higher than 99.2% in the load range of 20–120%, which is highly consistent with that of the simulation. The optimised burner could automatically distribute air supply and facilitate stable combustion.

Performance curve available for non-steady flow through Venturi-like reverse flow diverter

A reverse flow diverter (RFD) consists of a driving nozzle, a diffuser, and a suction gap that separates the nozzle and diffuser. Thus, the RFD is a Venturi-like fluidic component with three ports. The jet flow emanating from the driving nozzle exit can entrain the ambient fluid and transport it to a high elevation. During this time, the flow through the RFD is non-steady, which makes it difficult to measure the flow depending on the pressure drop. In this study, a series of tests was carried out to evaluate this fluid flow with different contraction ratios, suction gap lengths, fluid properties, inlet flow rates, and inlet pressures. A performance curve was formulated that can be expressed as an exponential equation correlating the non-dimensional Euler number, pressure ratio, and suction factor. The performance curve is not affected by the driving nozzle exit diameter and suction length of the RFD. The performance curve makes it possible to measure the flow out of a RFD depending on the pressure drop.

A prescription for primary nozzle diameters for solar driven ejectors

There is a growing interest in ejector cooling systems driven by solar heat. One of the main problems with solar cooling using ejectors is that the ejector cannot operate well if the operating conditions stray from the design point temperatures. Ejectors with variable geometry have been proposed and modelling shows that they are able to increase the operating range of an ejector. In particular, ejectors with a variable primary nozzle throat diameter have been experimentally shown to enhance ejector performance.This paper extends the work of others to provide a means to design a primary nozzle with variable throat diameter and variable nozzle exit diameter. The algorithm is extended to account for the behaviour of the solar collector and vapour generator. In this way, the nozzle diameters are determined as a function of the operating conditions ambient temperature and solar radiation. This correlation provides the basis for a practical nozzle control system.

English

Jet impingement systems provide an effective means for the enhancement of convective processes due to the high heat and mass transfer rates that can be achieved. The range of industrial applications that impinging jets are being used in is wide. In the annealing and tempering of materials, impinging jet systems are finding use in the cooling of hot metal, plastic, or glass sheets as well as in the drying of paper and fabric. Compact heat exchangers, with applications in the aeronautical or the automotive sector, often use multiple impinging jets in dense arrangements. In gas turbine applications, jet impingement has been routinely used for a long time. Because of increased thermal efficiency at high turbine inlet temperatures, many gas turbine components, such as rotor disks, turbine vanes and blades, or combustion chamber walls, are operated at temperatures well above highest allowable material limits. In order to assure durability and long operating intervals, effective cooling concepts are required for these highly loaded components.The current work involves studying of effect of spanwise jet-to-jet spacing on local heat transfer distribution due to an in-line rectangular array of confined multiple circular air jets impinging on a surface parallel to the jet plate computationally. Shear Stress Transport (SST) k-ω turbulence model is used. The flow, after impingement, is constrained to exit in two opposite directions from the confined passage formed between jet plate and target plate. Mean jet Reynolds numbers based on the nozzle exit diameter (d) covered is 10,000 and jet-to-plate spacings studied are d, 2d and 3d. Spanwise pitches considered are 2d, 4d and 6d in steps of 2d keeping the streamwise pitch at 5d. Length-to-diameter ratio of nozzles of the jet plate is 1.0. For all the configurations, the jet-plates have ten spanwise rows in streamwise direction and six jets in each spanwise row. The results obtained are validated against the experimental data available in the open literature.

공기의 자가흡입에 의해 마이크로버블을 발생시키는 보텍스 노즐에 대한 실험적 연구

This experiment was a study of a Vortex nozzle designed to produce micro-bubbles due To investigate air self-suction and the generation of micro-bubble by the Vortex nozzle, the dimensions of air intake region, the nozzle shape, and the nozzle exit diameter (dn=5,7,9.2,12.3mm)werevaried. The air self-suction rate was ~1,000 to 2,000 cc/min at the orifice nozzle (7 mm), and ~100 and ~22 cc/min at the sector nozzles (9.2 and 12.3 mm, respectively). The most bubbles were detected in the orifice nozzle, but bubbles less than 50 μm were found in the 12.3-mm sector nozzle. The dissolved oxygen in the tank water was much greater in Case 2 than in Case 1, at both the orifice and sector nozzles. Moreover, the reduction rate of dissolved oxygen was found to be less at the sector nozzles, than at the orifice nozzle.

Influence of High-temperature Air on Three-dimensional Nozzle Structure Design

In this paper, the exit diameter of nozzle is Φ 1.4 m, and the Mach number is 4.0; the nozzle is used in high-speed free jet wind tunnel for engine test with high temperature and pressure air and the mixture of heater combustion as working medium; The mixture is high temperature gas, mainly contains CO2,N2 and H2O. In the process of nozzle structural design, consider the interaction of radiation heat transfer and convection heat transfer fully; heat transfer problems aimed at the nozzle in complex gas, solid, liquid multiphase flow, form the calculation model of the radiation- convection - steady state – convection. Calculated by engineering and Ansys methods, The results show that, the convection heat transfer has an important effect on the air- surface by the high-temperature air in the entrance and the thorat of nozzle; Convection heat has a great influence on the air-surface temperature distribution of nozzle. It must be applied to the solution of temperature field in the nozzle structure design.A great deal of experiments show that, the temperature of the nozzle entrance and exit on the air-surface is close to the calculation results. The experimental results show that the nozzle works very well. In this paper, the calculation is described in details. The teat transfer calculation and some typical experimental results of three-dimensional nozzle and the photographs ofthe nozzle are also presented.