Outlet Throat Research Articles

Parametric Influence on Rotating Detonation Combustion: Insights from Fast Reactive Euler Simulations

A two-dimensional unsteady reactive Euler solver is employed to model rotating detonation combustion (RDC). A baseline case is chosen, and several combustor geometric and design parameters are varied individually in order to assess their effect on flowfield structure, exhaust flow properties, and performance. The parameters of interest are the perimeter and axial lengths of the combustor annulus, mass flux, outlet throat area, air injector throat area, and equivalence ratio. Quantification of the isentropically available work (IAW) in the exhaust flow is employed as a performance criterion. IAW is primarily affected by mass flux and outlet throat area through the effects of one-dimensional flow and, to a lesser degree, by perimeter and axial length through changes in the fraction of the flow that experiences irreversible shock processing. For all cases in the present study, this fraction appears to be solely determined by the ratio of detonation height to axial length. This ratio is also highly correlated to the angle of the oblique shock and the strength of the flow fluctuations. The predicted wave speed is between 90 and 95% of the Chapman–Jouguet velocity for a range of equivalence ratios between 0.6 and 1.4.

Phosphor thermometry evaluation of heat transfer enhancement on a hot plate achieved by a vortex-based fluidic oscillator

Recently, a vortex-based feedback fluidic oscillator has been proposed as an alternative to conventional feedback fluidic oscillators. This study aimed to compare the heat transfer performance of a newly designed fluidic oscillator with that of conventional feedback fluidic oscillators with and without an output diffuser using phosphor thermometry. To obtain the instantaneous temperature field in a wide range of high temperatures, a lifetime-based method was employed in two-dimensional phosphor thermography, with Mg4FGeO6: Mn serving as the sensor material and being excited by a UV-LED. A high-speed camera was used to capture images of the hot plate at 4,000 fps. The calibration test was conducted in the temperature range of 25–325 ˚C, and the results were compared with data from thermocouples. The study investigated the impact of the mass flow rate and throat-to-plate distance ratio of three fluidic oscillators to obtain the optimum Nusselt number. The results demonstrated that the newly designed fluidic oscillator exhibited significantly superior cooling effects in comparison to other types of fluidic oscillators. At the lowest ratio of the throat-to-wall distance to the outlet throat height (Z/D = 4.5) and a flow rate of 100 Lpm, the vortex-based fluidic oscillator demonstrated 78 % and 45 % higher heat transfer rates compared to the conventional oscillator with and without an external diffuser, respectively. Furthermore, the newly designed oscillator was more sensitive to the mass flow rate and throat-to-plate distance ratio than the other oscillators.

Analysis on Propulsive Performance of Hollow Rotating Detonation Engine with Laval Nozzle

In the present study, an experimental performance analysis of hollow rotating detonation engines (RDEs) with Laval nozzles is carried out for the first time. Experiments of a hollow rotating detonation engine with a Laval nozzle were performed with a modular RDE at a backpressure condition of 1 atm. Two configurations with area ratios of the outlet throat to the inlet of and 2.7 have been tested with gaseous methane/oxygen as propellants. Three normalized metrics, usually used for evaluating the performance of conventional rocket engines, are introduced to analyze the performance deficit between the measured value of an RDE and the ideal value of an isobaric-combustion-based engine. These metrics allow for assessing the entire engine and each component separately. The metric analysis suggests a small outlet-to-inlet area ratio () is detrimental to the propulsive performance. To explain the mechanism, a gas-stratification flowfield model is further proposed. It is found that the unchoked region in the combustible gas layer, which is caused by unchoked injection on the injecting plate, is responsible for the performance deficit of the combustion chamber. This model is then validated by one-dimensional numerical simulations and experimental data. In addition, we also focus on the global performance, including the gross thrust, the specific impulse, and the utilization of the supplied stagnation pressure. The result implies a tradeoff space when choosing an appropriate .

Transient numerical study of CO2 two-phase flow in a needle adjustable ejector

Steady-state numerical modeling is mostly used for predicting the flow and transport characteristics in an ejector, but it may not be able to reflect the actual performances of an ejector when operating condition varies. Moreover effects of needle movement on the performances of an ejector is not very clear. In this study, a transient heterogeneous mixture model was developed for a two-phase CO2 needle adjustable ejector with motive nozzle inlet in supercritical, critical or sub-critical regions. The dynamic mesh method was used to control the needle movement, and the unsteady coupling solution between the needle movement and the flow field is solved for the adjustable two-phase CO2 ejector. Modeling results show that the transient modeling can predict dynamic performances of CO2 ejector more accurately than the steady-state modeling. Based on the transient modeling, it is found that as the needle moves further into the motive nozzle throat, effective nozzle throat area decreases, expansion angle of motive flow increases then decreases, the velocity at the motive nozzle outlet decreases then increases, and entrainment ratio decreases, then increases sharply, then decreases, finally become negative. High pressure at the motive nozzle inlet leads to high entrainment ratio owning to high velocity at the motive nozzle throat outlet. A sudden increase of pressure at the motive nozzle inlet in different thermodynamic state regions (supercritical, sub-critical) leads to different dynamic performance responses and oscillation times of ejector. The mechanisms of boundary layer separation and backflow vortices as well as shock waves were explored to explain the suction flow chocking phenomena. This study is helpful to understand flow mechanisms inside the CO2 ejector, and improve optimal design and control of an adjustable two-phase CO2 ejector in variable operating conditions in practice.

Математична модель переміщення зрізаної гички коренеплодів цикорію в направляючому каналі

The increase in the production of root crops of chicory, which is a valuable technical crop, is restrained by the low level of mechanization of the main technological processes of their collection. The increased content of vegetable impurities or the remains of ghee in the collected root crops of chicory significantly reduces the quality of the raw material and, accordingly, the output of its processing products. On the basis of the analysis of the technological process of cutting root vegetables with L-shaped knives of a rotary vegetable cutter, a mathematical model was developed that functionally describes the movement of the cut vegetable in the guide channel of the vegetable cutting machine depending on the structural and kinematic parameters of the working organs of the cutting apparatus. On the basis of the solution of the mathematical model, the equation of the profile of the surface of the casing of the guide channel was obtained from the conditions of equal post-shock velocities and equal speeds of movement of the cut-off beam. It was established that the most acceptable is the profile in which the angle of collision, or the angle between the direction of the pre-impact velocity vector and the tangent to the profile of the guide channel at the point of impact is equal to 25 degrees, while the height of the profile of the guide channel is 1.2 m. For the value of the angle between in the direction of the pre-impact velocity vector and tangential to the profile of the guide channel at the point of impact 30...35 degrees. the initial speed of movement of the cut particle of the string is in the range of 9.5...10.5 m/s, and at the exit from the outlet throat – 2.5...3.5 m/s, while the time of moving the string along the guide channel is 0.15 ...0.2 s.

On the wave propagation modes and operation range in rotating detonation combustor with varied injection and outlet throat

The rotating detonation combustor (RDC) has received remarkable attention in the aerospace community. In this work, an experimental RDC model supplied by liquid kerosene and oxygen-enriched air is established. A parametric survey is performed with different injection throats, outlet restrictions, and equivalence ratios to analyze the rotating detonation wave propagation modes comprehensively. Dynamic pressure transducers and a high-speed camera are both employed to identify wave modes synchronously. Overall, the propagation modes are found to be highly dependent on the injection throat and combustor outlet restriction. With a large injection to annulus area ratio of 0.3, a single-wave mode is characterized when no restriction is added at the combustor outlet. Reducing the outlet area leads to a decrease in the wave frequency and a narrower steady rotating detonation propagation regime. The propagation stability of the rotating detonation is strengthened when the injection to annulus area ratio decreases to 0.2. A dual-wave collision mode and a four-wave collision mode are observed, depending on the outlet restriction. A preliminary stable RDC operation range correlated with outlet to injection throat area ratio and equivalence ratio is achieved. Furthermore, an interval value of the outlet to injection throat area ratio is proposed to reach the potential positive total pressure gain. These findings should serve as the reference for RDC configuration design in air-breathing and gas-turbine propulsion systems.

Optimal technical analysis of vacuum ejector for passive hydrogen recovery

In this study, the numerical analysis and experimental measurements are conducted on the internal flow field and temperature distribution of ejectors with different throat diameters. The computational fluid dynamics (CFD) is used to simulate different ejectors and investigate the effects of Mach number, pressure, and temperature distributions. The hydrogen Entrainment Ratio (ER) of ejectors is also measured for proton exchange membrane fuel cell applications. The experimental measurements and simulations of the hydrogen Entrainment Ratio of the ejectors showed that the recovery efficiencies are 59%, 53%, and 33% for the pipe diameters of 0.5, 0.7, and 1.0 mm at the inlet pressures of 340 kPa, respectively. In different area ratios, the larger area ratio of the nozzle leads to greater difference between the diameter of the throat and the diameter of the throat outlet. This causes a smaller recovery rate. In the internal flow field of the ejector, higher recovery rate can be achieved by using the closer location of the positive shock wave to the nozzle outlet.

Parametric study of a fluidic oscillator for heat transfer enhancement of a hot plate impinged by a sweeping jet

• CFD and experimental studies are conducted on the heat transfer of fluidic oscillators. • Effect on the heat transfer rate due to new geometrical changes is studied. • Experimental study was conducted to verify the numerical results for the fluidic oscillator. • Heat transfer rate was increased by 140% when removing the external diffuser. • Heat transfer was decreased when increasing the distance ratio and divergence angle. Many studies have looked at the effects of various geometrical parameters of fluidic oscillators on the heat transfer rate of a hot plate impinged by a sweeping jet. In this research, Ansys-Fluent software was used to solve two-dimensional Unsteady Reynolds-Averaged Navier-Stokes ( URANS ) equations with a k-ω (SST) turbulence model to study the effect on the heat transfer rate of a hot plate due to some new geometrical changes, such as removing the external diffuser, changing the divergence angle of the external diffuser, and changing the distance from the outlet throat to the hot plate. An experimental setup was provided to verify the numerical results for the fluidic oscillator with an external diffuser. To measure the temperature inside and near the surface, 22 thermocouples were used inside a thick hot plate, which was impinged by a sweeping jet. Three distance ratios ( X/D = 4.5, 5.5 and 7.5) and four divergence angles ( θ = 180°, 50°, 70°, and 90°) were numerically analyzed as the geometrical parameters at Reynolds number of 30,000, 60,000, and 120,000. The results revealed that the heat transfer rate increased by 140% when removing the external diffuser at X/D = 4.5 and Re = 60,000, while it decreased when increasing the distance ratio and divergence angle.

Numerical study on energy conversion characteristics of molten salt pump based on energy transport theory

Molten salt pump (MSP) used in concentrating solar power (CSP) system to circulate the molten salt. The operation of MSP needs to understand the energy conversion characteristics in the flow field. In this study, the energy conversion characteristics of MSP were investigated based on energy transport theory. A significant portion of power is consumed in the propulsion of pressure between the inlet throat to the outlet throat of the impeller passage. The increase in the energy of medium by the Lamb vector divergence mainly occurs on the rear of the impeller passage. Whereas the enstrophy dissipation area is primarily located in the suction surface area at the impeller outlet. In addition, the pressure propulsion power is critical for energy transfer in the impeller, while the contribution of Lamb vector divergence and enstrophy dissipation is limited. It was observed that the distribution of the three energy transport dynamic parameters have a high degree of coincidence irrespective of the medium density, which indicates that the density of the medium does not have a significant impact on the law of energy conversion. Therefore, when the geometrical characteristics of the impeller are determined, the energy conversion characteristics of different medium do not change significantly.

Numerical Study on Energy Conversion Characteristics of Molten Salt Pump for Concentrating Solar Power Based on Energy Transport Theory

Molten salt pump (MSP) used to circulate the molten salt in concentrating solar power (CSP) system. The operation of MSP needs to understand the energy conversion characteristics in the flow field. In this study, the energy conversion characteristics of MSP were investigated based on energy transport theory. A significant portion of power is consumed in the propulsion of pressure between the inlet throat to the outlet throat of the impeller passage. The increase in the energy of medium by the Lamb vector divergence mainly occurs on the rear of the impeller passage. Whereas the enstrophy dissipation area is primarily located in the suction surface area at the impeller outlet. In addition, the pressure propulsion power is critical for energy transfer in the impeller, while the contribution of Lamb vector divergence and enstrophy dissipation is limited. It was observed that the distribution of energy transport dynamic parameters have a high degree of coincidence irrespective of the medium density, which indicates that the density of the medium does not have a significant impact on the law of energy conversion. Therefore, when the geometrical characteristics of the impeller are determined, the energy conversion characteristics of different medium do not change significantly.

Enhancing the Aggressive Intensity of a Cavitating Jet by Introducing Water Flow Holes and a Long Guide Pipe

Abstract It is known that the geometry of the nozzle has a great effect on the aggressive intensity of a cavitating jet. In previous reports, various nozzle geometries were proposed, and improvements made to the aggressive intensity were reported. However, no detailed description of the reasons why the aggressive intensity is improved by these various geometries was given. In this study, we conducted erosion tests on pure aluminum Japanese Industrial Standards JIS A1050P using 11 different nozzles with different geometries downstream from the throat outlet in order to understand the effects of the nozzle geometry on the aggressive intensity. In addition, in order to investigate the characteristics of the cavitating jet produced by each nozzle, measurements of the erosion areas, images of the cavitating jet using a high-speed video camera, and measurements of the impingement pressure of the cavitating jet were taken, and correlations between the parameters were obtained. It was found that the nozzle with the largest mass loss was a nozzle with water flow holes near to the throat outlet and a long guide pipe (LGP). The mass loss was 2.5 times that of the previously reported optimum geometry nozzle. Very high correlations were obtained between the mass loss, the inner diameter of the annular erosion area, the impingement pressure measured at the same standoff distance and the cavitation cloud lifetime. Based on these results and the images of the cavitating jets taken with the high-speed video camera, a new cavitating jet progression process is proposed.

An empirical model for stagnation pressure gain in rotating detonation combustors

This work investigates the stagnation pressure gain in rotating detonation combustors (RDC) and its dependency on the geometry and mass flux of the combustor. Using a Kiel probe to directly measure stagnation pressure in the high-enthalpy exhaust stream, results are presented for a systematic variation of these parameters. The best-performing configuration achieved a pressure gain of −8%. A comparison with thrust-based equivalent available pressure data from literature shows that the Kiel probe measurements are in good agreement. It is observed that pressure gain increases with increasing air injector area, decreasing outlet throat area, increasing combustor mass flux, and is seen to be dependent on the operating mode. The data are then used to obtain an empirical model that describes pressure gain as a function of the three variables of injector area ratio, outlet area ratio, and combustor mass flux. The model is compared with measurements in this combustor and others, and is used to predict the pressure gain boundaries and to assess design corridors that potentially achieve positive pressure gain.

Experimental and numerical studies on metrological characteristics of swirlmeters with different swirler helix angles in a gas–solid two-phase flow

Swirlmeters are widely used to measure natural gas because of their simple structure, absence of internal moving parts and high measurement accuracy. However, fine particles in natural gas can affect swirlmeters’ metering accuracy. Hence, this study evaluated the metrological characteristics of swirlmeters measuring gas–solid two-phase flow with fine particles and different swirler helix angles. Experiments and simulations for swirlmeters with different solid–gas mass ratios and helix angles were performed. The results demonstrated that the swirlmeter meter factors decreased and pressure losses increased as the solid–gas mass ratio increased. With different solid–gas mass ratios, the most effective sensor detection position was at the throat outlet a half radius from the centre of the runner. The swirler with a smaller helix angle could significantly increase the meter factor, while the swirler with a larger helix angle could significantly decrease pressure losses. The swirlmeter internal flow losses were mainly derived from the swirler.

Performance analysis of a rotating detonation combustor based on stagnation pressure measurements

This study explores the effect of differing inlet and outlet boundary conditions on the operation and performance of a rotating detonation combustor (RDC) over an annulus mass flux range of 50 to 210 kgs−1m−2 and equivalence ratios of 0.7, 1.0, and 1.3. The RDC is equipped with either a uniform outlet restriction or with a set of nozzle guide vanes to simulate turbine integration. Stagnation pressure data from Kiel probes placed in the high-enthalpy exhaust flow are presented for the operational envelope. The RDC’s operation is categorized into different modes distinguished by the number of co- and counter-rotating combustion waves in the annulus. With increasing mass flux, a typical progression proceeding from a pair of counter-rotating waves, to a single detonation wave, and then further to multiple co-rotating waves is observed with wave speeds reaching up to 84% of the CJ velocity. It is shown that a choking condition at the outlet throat correlates with the transition from two counter-rotating waves to a single wave detonation regime. The channel Mach number is then calculated from measured pressure ratios and is shown to agree with area ratio-based estimates. The pressure gain of the RDC is expressed as the stagnation pressure change from the air plenum to the outlet throat, and it is shown that the specific operating mode of the device – in conjunction with the chosen injector and outlet area ratios – can significantly decrease the pressure gain performance in some cases, while not significantly affecting it in others. While no positive pressure gain was achieved in the experiments, the presented experimental data compare well with numerical results of similar boundary conditions and underline the importance of minimizing injector pressure loss while applying outlet restrictions to the combustor. The data also suggest that specific geometric combinations may lead to adverse modes such as longitudinally pulsing combustion, resulting in a reduction in the measured pressure gain relative to numerical results. This observation occurs more often for geometric combinations which are the most promising for exhibiting positive pressure gain, and suppressing these modes will be an important topic to achieving this goal. It is further shown that transition regions exist between modes of one and multiple co-rotating waves, and that wave multiplication may be necessary to unlock further increases in the pressure gain.

Effect of Wet Steam on Aerodynamic Performance of Low-Pressure Exhaust Passage with Last Stage Blade

The condensation of wet steam has important effects on the behavior of the flow field. To evaluate the aerodynamic performance of exhaust passage influenced by wet steam phase change condensation, a numerical investigation was conducted. Taking a 600 MW steam turbine as an example with consideration of the wet steam from the last stage blade and the steam exhaust of the BFPT (boiler feed water pump turbine), the governing equations of wet steam two-phase flow were adopted by the Eulerian-Eulerian approach. Results show that the wetness in the stator domain increases gradually while the wetness in the rotor domain varies little on the pressure surface and is in small increment on the suction surface. The velocity uniformity can be improved at condenser throat outlet as the mass flow or wetness increases. Moreover, the trend to improve the aerodynamic performance of exhaust passage benefits from the improvement of wetness at the last stage blade inlet. Conversely, with the increment of wetness at the BFPT inlet, the static pressure recovery coefficient reduces by 5.8% and the total pressure loss coefficient increases by 2.4%, resulting in a reduction of aerodynamic performance of exhaust passage.

Properties of a sweeping jet emitted from a fluidic oscillator

This experimental study investigates the flow field and properties of a sweeping jet emitted from a fluidic oscillator into a quiescent environment. The aspect ratio of the outlet throat is 1. Stereoscopic particle image velocimetry is employed to measure the velocity field plane-by-plane. Simultaneously acquired pressure measurements provide a reference for phase correlating the individual planes yielding three-dimensional, time-resolved velocity information. Lagrangian and Eulerian visualization techniques illustrate the phase-averaged flow field. Circular head vortices, similar to the starting vortex of a steady jet, are formed repetitively when the jet is at its maximum deflection. The quantitative jet properties are determined from instantaneous velocity data using a cylindrical coordinate system that takes into account the changing deflection angle of the jet. The jet properties vary throughout the oscillation cycle. The maximum jet velocity decays much faster than that of a comparable steady jet indicating a higher momentum transfer to the environment. The entrainment rate of the spatially oscillating jet is larger than for a steady jet by a factor of 4. Most of the mass flow is entrained from the direction normal to the oscillation plane, which is accompanied by a significant increase in jet depth compared to a steady jet. The high entrainment rate results from the enlarged contact area between jet and ambient fluid due to the spatial oscillation. The jet’s total force exceeds that of an idealized steady jet by up to 30 %. The results are independent of the investigated oscillation frequencies in the range from 5 to 20 Hz.

Numerical modeling of internal flow in a fluidic oscillator

A numerical investigation of a fluidic oscillator was performed to understand the unsteady internal flow field and geometrical effects on the performance using three-dimensional unsteady Reynolds-averaged Navier-Stokes equations. Effects of the two geometrical parameters, i.e., the inlet width of the mixing chamber and outlet throat width, on peak jet velocity ratio at the exit and pressure drop through the oscillator, were evaluated. The unsteady simulation was performed using shear stress transport turbulence model with air as working fluid at Reynolds number 30000. Computational results showed good qualitative and quantitative agreements with available experimental results for the flow structure and frequency of the oscillating jet. Results of the parametric study suggested that the inlet width affected significantly the flow in the fluidic oscillator, while effects of the throat width on the performance parameters were not remarkable.

Three-Dimensional Numerical Simulation of Steam Turbine Exhaust Channel Considering Pipeline and Four Wall Reinforcement

A three-dimensional numerical simulation of the internal structure of the exhaust channel was carried out by using Fluent software. A three-dimensional model was established by step-by-step simulation of the internal structure of the exhaust pipe performance impact. The results show that the support pipe and the four-wall stiffeners increase the complexity of the flow field. By blocking the effect of the vortex, the static pressure recovery capacity of the exhaust cylinder is improved and the uniformity of the flow rate of the throat outlet section is reduced, but the total pressure loss was increased.

Studying the Effect of the Air-Cap Configuration in Twin-Wire Arc-Spraying Process on the Obtained Flow Characteristics Using Design of Experiment Oriented Fluid Simulation

The computational fluid dynamics approach is adopted in this work using the design of experiments to reveal the effect of the air-cap configurations on the obtained gas velocity, the shear stresses, the high velocity zone, and the convergence of the obtained spraying plume in the twin-wire arc-spraying process. The parameters, which are revealed to optimize the air-cap configuration, are the throat diameter, the convergence angle of the throat inlet, the throat length, and the distance between the throat outlet and the intersection point of the approaching wires. The throat length is dependent upon the other configuration parameters. Outlet gas velocity, the turbulence in the flow, and the exerted shear stresses at wire tips are directly affected by the dominating flow regimes near the intersection point of the approaching wires. The presence of wires and the contact tips in the gas flow has enormous impact on the obtained flow characteristics. Air-cap throat diameter and the distance between throat outlet and intersection point determine the shape and length of the obtained high velocity zone in the spraying plum.

Numerical investigation of supersonic flow breakdown at the inlet duct throttling

The work presents the results of investigating the process of supersonic flow deceleration in a duct of the two-dimensional inlet throttled by variation of the outlet cross-sectional area. An inlet with three external compression shock waves designed for the freestream Mach number Md = 7 was considered as an example for the investigation. A one-dimensional analysis of the conditions for realization of the supersonic flow deceleration regimes in the inlet duct with two throats — in the inlet entrance and at the inlet duct outlet, has been carried out. The parametric numerical computations of two-dimensional inviscid or turbulent flows in the inlet were performed with the use of the Euler and Navier—Stokes codes of the program package FLUENT. The critical conditions for the nonuniform flow in the outlet throat bringing to choking the inlet duct were determined.