Nozzle Flow Field Research Articles

Enhancement of Film Cooling Effectiveness in a Supersonic Nozzle.

Film cooling as applied to rocket nozzles is analyzed numerically with emphasis on the assessment of the effect of the mixing of coolant with the hot stream. Cooling performance, as characterized by cooling effectiveness, is studied for three different coolants in the three-dimensional, turbulent flow field of a supersonic convergent-divergent nozzle operating with a hot stream temperature of 2500 K over a range of blowing ratios. The coolant stream is injected tangentially into the mainstream using a diffuser-type injector. Parameters influencing the effectiveness, such as coolant injector configuration and mixing layer, are analyzed. Thermal and species mixing between the coolant and the mainstream are investigated with regard to their impact on cooling effectiveness. The results obtained provide insight into the film cooling performance of the gases and the heat transfer characteristics associated with these three gases. An injector taper angle of 30° results in the most effective cooling among the configurations considered (0°, 15°, 30° and 45°). Mixing of the coolant with the hot stream is examined based on the distributions of velocity, temperature and species. The higher values of cooling effectiveness for Helium are attributed to its thermophysical properties and the reduced rate of mixing with the hot stream. The results further indicate that through optimization of the blowing ratio and the coolant injector configuration, the film cooling effectiveness can be substantially improved.

Influences of geometric parameters on serpentine nozzles for turbofan

Serpentine nozzles possess excellent advantages in improving the stealth ability of aero-engine exhaust. For a real turbofan, the flow characteristics of the serpentine nozzle are evidently affected by the geometric parameters and the complex exhaust mixer. This is an issue that needs to be seriously considered. The aim of this paper is to investigate the influences of the critical geometric parameters on the serpentine nozzles for turbofan. The detailed flow field of the serpentine nozzle for a small-scale model is precisely measured. The influence of the ratio of axial length to inlet diameter on the flow field and on the aerodynamic performance of the serpentine nozzle is numerically explored. Results show that the pressure on the upper wall first drops rapidly and then ascends with the local minimum occurring at the first inflection. The relative error between the numerical prediction and the experimental data is less than 2%. The calculated distributions of the expansion-shock waves and the jet shear layers are highly consistent with the schlieren flow visualization data. Thus, the reliability of the numerical method is effectively confirmed. The internal flow and the external jet features of the serpentine nozzle are extremely non-uniform. Such poor uniformity is reflected in the phenomena including the existence of the local high-shear-stress regions and the high-velocity regions, the multiple bending of the limiting streamlines, as well as the velocity fluctuation of plume core. The aerodynamic performance of the serpentine nozzle first enhances greatly and then stays unchanged as the value of L/D rises. The vortex loss and the shock loss both reduce evidently owing to the flow separation and the disappearance of the shock wave during the rise of L/D from 2.2 to 2.4. The value of the discharge coefficient and the thrust coefficient increases by 1.5% and 2.1%, respectively. The length of the plume core is effectively shortened due to the disappearance of the shock wave inside the nozzle.

Numerical study of flow establishment process of engine in a shock tunnel

In this paper, an unsteady numerical simulation of the full-scale flow field establishment process of a scramjet in shock tunnel is carried out. The simulation covers from the driving process of the shock tube to the flow field establishment of nozzle and engine, and combines the chemical reaction of air. The feasibility of the calculation method is verified by comparing the pressure from simulation results and the experimental ones that measured in the shock tube. The results show that in the shock tube, the total pressure at the nozzle inlet is formed by the incident shock wave, the shock wave reflected by the diaphragm and the shock wave train caused by the nozzle high pressure. After the nozzle flow field is established, the Mach number of the core flow reaches the design value of 9.0, and the total pressure of the core flow reaches 30 MPa. By comparing the results of flow fields, wall pressure distributions and drag coefficients with the steady case, we show that the flow in test section approaches steady state in 16 ms, which includes the shock tunnel and nozzle starting time. The non-dimensional characteristic establishment time of the engine is about 4 and it is closed to that of the flat plate case.

Catalytic wall effects for hypersonic nozzle flow in thermochemical non-equilibrium

This paper investigates the effects of wall catalytic activity in hypersonic nozzle flows. Non-equilibrium Navier–Stokes-Fourier equations were here applied within a density-based algorithm in the OpenFOAM framework. The numerical model was validated using different test conditions conducted at NASA EAST facility and General Electric Research Laboratory. After confirming the reliability of the numerical model, a numerical investigation on the wall catalytic effects on the flow parameters using the Scirocco Plasma Wind Tunnel was performed. Four nozzles with different expansion ratios were extensively tested. It was verified that higher expansion ratio nozzles experience a greater wall catalytic effect on the flow properties. Particularly, doubling the expansion ratio causes the difference between a non-catalytic and a fully catalytic wall to increase in 21% for Mach number and 25% for trans-rotational temperature and static pressure. Furthermore, the results of this investigation allow us to define a new criterion by which to consider if the wall catalytic effects are or not important in the nozzle flow fields. It was found that catalytic effects in the core flow are negligible when simulating nozzles with expansion ratio below 186 and Mach number below 8.6. As the expansion ratio increases, the thermal boundary layer thickness also increases and the atoms recombination that occur in that region have more influence on the core flow. In these cases, it is then necessary to take into account the wall catalytic activity to achieve a better estimation of the flow properties at the nozzle exit and in the test cell. • Catalytic wall effects in high enthalpy wind tunnels are numerically investigated. • Numerical simulations of hypersonic nozzles in thermochemical non-equilibrium are performed. • The recombination reactions at fully catalytic walls changes the nozzle core flow. • Catalytic wall effects are negligible for expansion ratio below 186 and Mach number below 8.6.

Effects of cryogenic gas jet cooling on milling surface roughness and tool life for GH4169 alloy additive manufacturing parts

Hybrid additive and subtractive manufacturing is development in metal additive manufacturing techniques, wherein the dry cutting cooling method for subtractive cutting is one of the key technologies. To improve the milling performance of GH4169 alloy (namely Inconel 718 nickel-based superalloy) additive manufacturing parts, a dry cutting cooling method with a cryogenic gas jet and its effects on the cutting performance were investigated in this study. The theoretical model of the cryogenic gas jet flow was established, and the geometric characteristics, motion characteristics, and temperature distribution of the jet flow were analyzed. Meanwhile, considering the design of the nozzle outlet, the jet flow core length with a single nozzle and jet flow field envelope effect on the cooling heat transfer process with multiple nozzles were analyzed using a finite element simulation. Then, milling experiments on GH4169 alloy additive manufacturing parts with different cryogenic gas jet flow parameters were carried out. To reduce tool wear and the machined surface roughness of various parts, the jet flow parameters were optimized using the response surface analysis method. The effects of the milling feed direction on the tool wear and machined surface roughness were investigated. Furthermore, the tool wear morphologies were observed under different continuous milling times. The chemical compositions of the worn zone and tool wear mechanism were analyzed. The results show that cryogenic gas jet cooling can significantly improve the tool life and machined surface roughness of parts for GH4169 alloy additive-manufacturing-part milling, and the continuous cutting time within the tool wear allowance can reach approximately 50 min.

Numerical analysis of the flow field in a planar nozzle for different divergent angles

In the present work, the flow field is analysed for Mach number, pressure and temperature in 2D computational domains for a planar nozzle of symmetrical geometry as used in the experimental tests for cold (air) flow. The study has been considered for three mean angles of the divergent section: α = 9°, α = 11.01° and α = 13°, and for four pressure ratios: NPR = 2.412, NPR = 3.413, NPR = 5.423 and NPR = 8.78. For the numerical simulation of the turbulence in the presence of shock waves, the RANS model, the Sutherland equation and the Spalart-Allmaras turbulence model were used in the ANSYS-Fluent R16.2 code. The results obtained show fluctuations at the intersections of the internal shocks in the divergent, and the fluctuation decreases as the angle of the divergent increases. For NPR = 3.413, NPR = 5.423 and NPR = 8.78, the Mach number at the nozzle exit is the same, where for α = 11.01° Mach 2.00 was obtained, and based on this reference, for α = 13° there is an increase in velocity of 4.15% and for α = 9° a decrease in velocity of 3.78%. The lowest pressure and temperature drop occurs at the nozzle outlet for α = 13°.

Numerical simulation of particle erosion in the internal flow field of solid rocket motor nozzle using Rocstar

Solid composite propellants often contain metal particles, such as aluminum particles, and the internal flow field in a solid rocket motor is a typical gas–solid two-phase flow field. In this study, to address the problem of the erosion of particles on the wall during the working process of an engine, a particle erosion model was established based on the interaction mechanism between the particles and the wall. From the perspective of particle dynamics, the interaction mechanism between the moving particles and the wall was analyzed. The force of the particles on the wall surface was obtained, and a formula for solving the particle erosion rate was deduced by using the strength theory and the energy conservation principle. It was combined with Hertz’s contact theory to analyze the factors influencing the erosion rate. In this paper, the particle erosion experiments revealed not only the relationship between erosion rate and erosion angle but also the correlativity between erosion rate and particle concentration. In addition, the experimental results are consistent with the deduced results, which proves the reliability of the model established in this paper. The multiphysics simulation program Rocstar, developed by the Center for Simulation of Advanced Rockets at the University of Illinois, was used to perform a numerical simulation of the two-phase flow in the Jet Propulsion Laboratory nozzle. The results agreed well with the literature and the experimental data. The feasibility and accuracy of the calculation of the gas-phase and two-phase flow fields of the solid rocket motor nozzle were confirmed, laying the foundation for the numerical simulation of the entire process of the full flow field of the engine.

Impact of reattachment surface characteristics on the flow field generated by slot jet reattachment nozzle – A numerical study

Slot jet reattachment (SJR) nozzle is a novel nozzle design that overperforms the regular impingement nozzles or perforated plates for heat transfer and drying, heating or cooling applications of moist materials. The SJR nozzle is a viable design to dry fragile products such as food and paper. Mesh-type conveyor belts are commonly used in the food industry. There is a need for understanding how the SJR nozzle performs with mesh-type conveyor belts because prior studies have solely considered solid surfaces. Therefore, an extensive numerical study is performed to solve the flow field of the SJR nozzle with an exit angle of +45° on top of a mesh-type belt with and without products using COMSOL Multiphysics® without including heat transfer. Turbulent fluid flow is theoretically modeled using the k-ɛ turbulence model for the SJR nozzle. The numerical predictions are validated with experimental data for stationary surface. Six different cases are studied to capture the effects of the presence of products on the belt and the conveyor belt speed. Additionally, the presence of an SJR nozzle on the bottom of the belt with and without a lateral offset is studied. The mass flow rate escaping underneath the belt is compared to the total mass flow rate at the nozzle exit, shear stresses are compared at three different surface velocities, and maximum force magnitudes as product travels are reported. The results show that the flow can reattach to the product surface regardless of surface motion, but reattachment characteristics depend on product orientation with respect to the SJR nozzle. Although significant mass flow escapes through the belt, the presence of products mitigates this loss. In addition, doubling the belt speed increases the shear stresses applied by the surface and decreases the average mass flow loss. Also, an additional SJR nozzle on the bottom of the belt almost cancels this mass flow loss even when there is a lateral offset between the nozzles.

Computational investigation of the effect of variable cowl length on the flowfield of conical aerospike nozzles

Computational investigation of the effect of variable cowl length on the flowfield of conical aerospike nozzles

Numerical investigation into fuel–air mixing characteristics and cold flow field of single hydrogen-rich Micromix nozzle

As a promising gas turbine combustor for hydrogen-rich syngas, Micromix combustor may produce new design criteria due to its novel structure. Therefore, the mixing characteristics and flow field of single Micromix nozzle with multiple micro-mixing tubes were studied numerically. The results showed that, the Large-Eddy simulation model was more accurate in cold-state prediction of Micromix combustor than the Reynolds averaged equations model. For mixing characteristics, mass diffusion had greater effect on mixing process of hydrogen-rich syngas than momentum-driven diffusion. With the increase of premixing distance, the effect of fuel–air momentum ratio gradually disappeared. And the difference in mixing characteristics was mainly caused by the shear-layer instability at the initial stage of jet. By reducing the jet-direction diameter of micro-mixing tubes, the mixing uniformity improved, indicating that the jet-direction mixing ability was weak, but there was an upper limit of the mixing uniformity. In addition, fuel hole shapes had obvious effect on vortex structure and vorticity, but little impact on mixing characteristics. For the cold flow field, there was a recirculation region between jets near the nozzle outlet, which was helpful for flame stabilization. Compared with the multiple circular jets, the axial scale of recirculation region formed by multiple elliptical jets was larger, the jet merging point and the combined point moved to the burner outlet.

New Designed Main Nozzle of Air-Jet Weaving Machine for Optimizing Air Consumption using CFD Simulation

The air-jet weaving machine is widely used in the textile industry and the main nozzle and acceleration tube is one of its key components of the machine. In this paper, the influence of some parameters, including the input air pressure with air inlet length and the structure of the nozzle core and its internal diameter, on the internal flow field of the main nozzle is analyzed to get the velocity of flow at the optimum air pressure that optimizing the air consumption. The flow field inside an air-jet loom main nozzle is studied by simulating the design of the main nozzle and acceleration tube, by means of a two-dimensional model implemented in the Ansys computational fluid dynamics (CFD) code Fluent, by designing the new main nozzle by working on the structural geometry of the main nozzle and acceleration tube. In order to determine the optimum air pressure for the required air velocity with optimum air consumption to flow weft yarn in an air-jet weaving machine.

Numerical simulations of internal flow fields in a nozzle with liquid fertilizer deep machinery

Fertilizing with water jet is a non-contact fertilization technique that uses high pressure water jet for hole-caving and fertilizing. In this article, an automatic liquid fertilizer deep machinery is proposed. The influences of three typical nozzles on the liquid fertilizer deep machinery were investigated via numerical simulations. The feasible water jet nozzle structures were obtained based on analysis and optimization of the main flaws of the four nozzles. A three-dimensional mathematical model of internal flow field in a high-pressure nozzle was established using the ANSYS software. Using the standard k-ε turbulent model, the internal flow field in the nozzle was simulated and the influences of nozzle parameters on the flow rate isogram and axial flow rate at the outlet of the flow field were studied. The results revealed that the axial flow rate at the outlet increased and then decreased as the convergence angle increased. The effects of cylinder section length on the axial flow rate at the outlet were negligible within a certain range. As the outlet diameter increased, the axial flow rate at the outlet decreased.

Computational Investigation of Effects of Side-Injection Geometry on Thrust-Vectoring Performance in a Fuel-Injected Dual Throat Nozzle

Dual-throat Nozzle (DTN) is known as one of the most effective approaches of fluidic thrust-vectoring. It is gradually flourishing into a promising technology to implement supersonic and hypersonic thrust-vector control in aircrafts. The main objective of the present study is numerical investigation of the effects of secondary injection geometry on the performance of a fuel-injected planar dual throat thrust-vectoring nozzle. The main contributions of the study is to consider slot and circular geometries as injector cross-sections for injecting four different fuels; moreover, the impact of center-to-center distance of injection holes for circular injector is examined. Three-dimensional compressible reacting simulations have been conducted in order to resolve the flowfield in a dual throat nozzle with pressure ratio of 4.0. Favre-averaged momentum, energy and species equations are solved along with the standard k- ε model for the turbulence closure, and the eddy dissipation model (EDM) for the combustion modelling. Second-order upwind numerical scheme is employed to discretize and solve governing equations. Different assessment parameters such as discharge coefficient, thrust ratio, thrust-vector angle and thrust-vectoring efficiency are invoked to analyze the nozzle performance. Computationally predicted data are agreed well with experimental measurements of previous studies. Results reveal that a maximum vector angle of 17.1 degrees is achieved via slot injection of methane fuel at a secondary injection rate equal to 9% of primary flow rate. Slot injection is performing better in terms of discharge coefficient, thrust-vector angle and thrust-vectoring efficiency, whereas circular injection provides higher thrust ratio. At 2% secondary injection for methane fuel, vector angle and vectoring efficiency obtained by slot injector is 8% and 34% higher than the circular injector, respectively. Findings suggest that light fuels offer higher thrust ratio, vector angle and vectoring efficiency, while heavy fuels have better discharge coefficient. Increasing center-to-center distance of injector holes improves thrust ratio, while having a negative effect on discharge coefficient, vector angle and vectoring efficiency. A comparison between fuel injectant of current study and inert injectant in the previous studies indicates that fuel reaction could exhibit substantial positive effects on vectoring performance. Secondary-to-primary momentum flux ratio is found to play a crucial role in nozzle performance.

Effect of air flow rate and temperature on the atomization characteristics of biodiesel in internal and external flow fields of the pressure swirl nozzle

In this study, the flow and spray of biodiesel in the swirl atomization nozzle were analyzed. The influence of primary air flow rate and temperature on the atomization characteristics in the internal and external flow fields of biodiesel was discussed through simulation and experiments. The velocity of biodiesel in the nozzle and mixing chamber were symmetrically distributed. With increasing primary air flow rate, the maximum speed area increased and the shape of the turbulent kinetic energy of biodiesel changed from columnar to funnel. When the primary air flow rate increased from 10 to 30 L/min, the Sauter mean diameter, (SMD, d32) decreased from 95 to 28 μm, and when it increased to 50 L/min, d32 changed slightly. With increasing fuel temperature, the spray velocity increased and the particle size gradually decreased, while the particle size of each interval remained almost unchanged over 45 °C. Therefore, the best primary air flow rate and temperature for the swirling atomization of biodiesel were 30 L/min and 45 °C. It was determined that the increase in air flow rate and temperature promoted the development of atomization flow field and the breaking of droplets in biodiesel, thus optimizing the swirling atomization of biodiesel.

Temperature distributions of internal flow and external jet fields of double serpentine convergent nozzle for turbofan

In order to clarify the temperature distribution of a double-serpentine convergent nozzle wall and the exhaust plume characteristics downstream the nozzle exit based on the real exhaust mixer configuration of a turbofan engine, the temperature distribution of the internal and external jet flow fields of the double-serpentine convergent nozzle are simulated numerically. The simulation results show that the coupling effect between S-shaped circular-to-rectangular profile and the exhaust mixer has a joint influence on the "hot streak" distribution of the double-serpentine convergent nozzle wall and the exhaust plume characteristics downstream the nozzle exit. The "Hot streak" is distributed in the shape similar to several ribbons in the central areas of the upper and lower wall of the second serpentine passage and in the exit area. The maximum value of temperature on the lower wall is 867 K and increases 25.1% compared with that on the upper wall. However, the average value of temperature of the lower wall is merely 7.1% higher than that of the upper wall. The "whale tail" high-temperature core area is formed on the exit plane of the double-serpentine convergent nozzle. It leads to two wide high-temperature jet flow areas in the high-temperature core area downstream the nozzle exit. The low-temperature flow occurs along the two sides of the exhaust plume core area due to the lateral-direction motion towards vortices.

Research on sputtering behavior of three beams coaxial laser cladding powder based on the interaction of lasers and powder

During laser cladding, a mutual coupling effect exists among the powder, carrier gas, shielding gas, and laser beam. The key to optimizing the cladding process is determining the effective utilization of the powder and revealing the interaction mechanism of the laser and the powder. In this paper, a continuous-discrete phase coupling model of the interaction between 316L powder, carrier gas, and protective gas in laser cladding is established, which is based on a three-beam coaxial powder feeder. Quantitatively reveals the influence of working distance, carrier gas flow rate, and shielding gas flow rate on the state of powder aggregation and the external flow field of the powder nozzle during the cladding process. To improve the utilization rate of the powder, the cladding process parameters were optimized by the orthogonal test method. A custom program of laser heat source function was written to calculate the temperature rise of powder under the interaction of the laser and the powder. The relationship between powder temperature and cladding process parameters was established. The powder aggregation shape obtained by the numerical simulation was compared with the actual aggregation shape. The temperature of the powder particles at a fixed position was collected by a noncontact infrared thermometer DT-8856H and compared with the simulation results to verify the validity of the established model. The research in this paper can effectively reveal the powder participation and the interaction mechanism of the laser and the powder during laser cladding. It can provide a theoretical basis for optimizing the cladding process parameters throughout the cycle and improving the quality of the cladding layer.

Statistical variation analysis of fuel spray characteristics under cross-flow conditions

Owing to cavitation inside the nozzle, spray breakup, and complex flow fields in the cylinder of a spark ignition engine, a certain degree of cycle-to-cycle variation (CCV) remains in different spray cycles under the same operating conditions, thereby affecting the spark ignition engine significantly. Therefore, the effect of cross-flow on the cyclic variation of the spray characteristics is investigated in this work. The CCV of fuel spray characteristics is evaluated via the statistical analysis of 30 repeated experiments under atmospheric pressure. First, the coefficient of variation (COV) is used to assess variations in the spray penetration, area, and optical thickness. Moreover, the effects of injection pressure and cross-flow velocity on the statistical characteristics of the spray are analyzed at the end of injection (EOI). Finally, a dimensionless “Ins number”, which is defined as the parameter of any spray characteristic at a certain time divided by the average experimental value, is proposed to evaluate the spray variation characteristics under cross-flow conditions. Therefore, when the absolute value of the Ins number approaches 1, the CCV of the spray characteristic parameters is low. Results show that the COV of the spray penetration is the largest in the initial stage of injection and then decreases gradually. Meanwhile, the COV of the vertical penetration can be categorized into two stages. Furthermore, it is discovered that the variation in the horizontal penetration is enhanced by the cross-flow and injection pressure at the EOI. In addition, in terms of the COV of the optical thickness, the variation on the windward side is greater, and the cross-flow enhanced the variation in the spray tip region. Most of the Ins numbers of the spray characteristics range from 0.9 to 1.1 (±10%) in this study, and they can provide data support for improving the accuracy of empirical prediction equations and models.

Numerical simulation of flow field in a Laval nozzle based on one-dimensional Euler equation

Numerical simulation refers to a computer research method which runs calculation based on a specific mathematical model to simulate actual physical processes. It is a powerful tool to analyse complex engineering problems. In this paper, a numerical method for solving the steady one-dimensional Euler equations using a two-step second-order difference scheme is developed. The method is implemented by a Python code. The method is applied to numerical simulation of flows in a Laval nozzle and used to investigate the influence of shapes of Laval nozzle. It is found that the physical quantities of the nozzle flow show a positive correlation trend with different throat positions. In terms of the temperature, density, and pressure, they increase during the initial evolutions, then reach the maximum point and produce significant fluctuations, indicating the flow flows into the transonic stage. Subsequently, those physical properties gradually tend to a stable value during the supersonic stage. Moreover, it is observed that the closer the throat is to the exit, the lower the Mach number at which it eventually stabilizes. Finally, a suggestion about the best shape of the nozzle which can realize the max efficiency is concluded. Despite using an inviscid flow model, the steady pressures are quite satisfactorily predicted over the range of frequencies studied.

Numerical Analysis of Flowfield in Linear Plug Nozzle with Base Bleed

A linear aerospike nozzle is a kind of altitude adaptive nozzle that has optimum performance over the entire operational range. In this work, flow characteristics of a linear plug nozzle and a truncated plug with 40% plug length are studied numerically. Different flow types associated with an increase in nozzle pressure ratio, corresponding wall pressure variation and shock patterns are studied. The effect of base pressure improvement with a secondary flow from the base (base bleed) of the truncated nozzle is also examined. Four base bleed points are considered, and the optimum bleed point is selected based on performance and base pressure improvement. The two-dimensional numerical model is solved using Reynolds-averaged Navier–Stokes equations with the Transition SST turbulence model. Validation shows that the present model is good enough at predicting the flow features associated with a linear plug nozzle. From the three different flow types associated with this nozzle, the transition from one type to other happens at lower nozzle pressure ratios with truncation due to the reduction in length of the plug. Thrust coefficient increased by 3.54% in the case of the bleed 3 configuration with a secondary flow of 2% of inlet mass flow rate when compared with 40% plug length without base bleed.

Optimal Design and Numerical Simulation of High Reliability Meltblown Die

Double-slit nozzles are widely used in meltblown equipment. During the production process, two streams of high speed, high temperature hot air are ejected from two slits on both sides of the spinneret and converge to stretch and refine the polymer melt extruded from the spinneret. If we know the changes of airflow temperature and velocity in the flow field, we can simulate the fiber stretching and refinement process and predict the fiber properties to understand the fiber stretching mechanism, so as to guide the optimization design of meltblown process and improve the product quality and cost saving. In this thesis, a new meltblown die nozzle flow field model is developed based on the existing meltblown double-slot nozzle structure, which was improved from the theoretical model of meltblown double-slot nozzle developed by Ting Chen et al. In this thesis, the calculation area is determined and divided into meshes, and the Reynolds stress model is selected to simulate the flow field numerically, and the velocity and temperature distribution of the flow field along the axis of the spinneret is obtained.