High-speed Jet Flow Research Articles

Innovative configurations for heat sink integrated with piezoelectric fans

Piezoelectric (PE) fans are gradually replacing conventional axial flow fans in the field of heat dissipation for microelectronics due to small size and high efficiency. However, the flow characteristic of PE fans was seldom considered when arranging heat sink fins, which could not utilize the fans’ advantages. Here, the design of fin arrangement based on the transient flow field generated by the vibration of dual PE fans in the channel was calculated and analyzed by CFD simulation and dynamic grid technology. Four zones with different flow field characteristics were found: Zones 1 and 4 which located inlet and outlet of the channel were Parallel flow zone. Zone 2 with vortices corresponds to the area ranges from the waist of blades to middle section of the channel was Multiple vortices flow zone. Zone 3 with high-speed vortices and jet flows corresponds to the area ranges from middle section of the channel to halfway downstream of blades region was Diffuse flow zone. Innovative configurations of heat sinks where fins arranged at the inlet and surrounding blades were designed according to the flow field characteristics: the loss of high-speed airflow to the inlet was prevented effectively and heat dissipation in the downstream heat sinks was dispersed by fins arranging in Parallel flow zone and Multiple vortices flow zone. The development and merging of high-speed vortices were strengthened by the inhomogeneous pin-fins arranging in Diffuse flow zone. The optimal coordination between the velocity field and the temperature gradient field among innovative configurations was found based on the field coordination analysis. Heat transfer performance was enhanced by new designs where the average temperature compared to conventional heat sink with PE fans was reduced by 16.7°. Our work provided a new fins arrangement to achieve uniform temperature distribution and high heat transfer performance for heat sink integrated with PE fans and would benefit the application in thermal management of high power devices integrated with PE fans.

Phase classification and transient effects of the start-up process of multi-functional pump station in pump mode

In the context of achieving the goal of carbon neutrality, multi-functional pump stations (MFPS) have been greatly developed as a new energy system in recent years. The MFPS can operate in forward direction in pump mode to pump water and in turbine mode in reverse direction to generate electricity. At present, the instability of the MFPS during start-up process (SUP) in pump mode has become the key to restricting the operating life and further development of MFPS. In this paper, based on the motion characteristics of the pump and the cut-off facility (COF), the SUP of the MFPS in pump mode is clearly classified. In order to reveal the transient effect during the SUP, the steady-state full characteristic experiment (SFCE) of the pump was carried out. The occurrence phase of the transient effect during the SUP is analyzed, and the deviation between the steady-state external characteristics and the transient characteristics is revealed. In this study, the evaluation formula of the start-up completion degree (SUCD) of the MFPS in pump mode is proposed for the first time, and the evaluation and identification of the start-up progress at different phases are completed. The results show that the water flow in the system is in a reverse flow state in the Phase I. The SUCD of Phase I is 17 %. In the Phase II, The high-speed jet flow in the pump flows to the inlet of the guide vane (GV), which gradually changes the mainstream direction in the GV. A certain vortex structure can be observed at the exit of the flap gate (FG). The SUCD of Phase II is 61 %. In the Phase I and II, the dimensionless head of transient simulation is much larger than that of SFCE. In the Phase III, the flow state in the impeller will gradually stabilize. The transient effect disappears and the pressure fluctuation intensity decreases. The SUCD of Phase III is 93 %. In the Phase IV, the separation vortex that persists from Phase I-III at the tail of the GV blades disappears. The diversion capacity at the gate increases, and significant annular flow can be observed near the FG.

Long-lived nitric oxide molecular tagging velocimetry with 1 + 1 REMPI.

The successful demonstration of long-lived nitric oxide (NO) fluorescence for molecular tagging velocimetry (MTV) measurements is described in this Letter. Using 1 + 1 resonance-enhanced multiphoton ionization (REMPI) of NO at a wavelength near 226 nm, targeting the overlapping Q1(7) and Q21(7) lines of the A-X (0, 0) electronic system, the lifetime of the NO MTV signal was observed to be approximately 8.6 µs within a 100-Torr cell containing 2% NO in nitrogen. This is in stark contrast to the commonly reported single photon NO fluorescence, which has a much shorter calculated lifetime of approximately 43 ns at this pressure and NO volume fraction. While the shorter lifetime fluorescence can be useful for molecular tagging velocimetry with single laser excitation within very high-speed flows at some thermodynamic conditions, the longer lived fluorescence shows the potential for an order of magnitude more accurate and precise velocimetry, particularly within lower speed regions of hypersonic flow fields such as wakes and boundary layers. The physical mechanism responsible for the generation of this long-lived signal is detailed. Furthermore, the effectiveness of this technique is showcased in a high-speed jet flow, where it is employed for precise flow velocity measurements.

CFD-DEM validation and simulation of gas–liquid–solid three phase high-speed jet flow

Gas–solid–liquid flows are central to many industrial and natural processes. This paper investigates high-speed particle-laden water jets using both numerical and experimental approaches. The study considers key parameters such as converging angles (from 5 to 60 degrees), solids mass fraction (from 0.1. to 0.3), and mean jet velocity (from 20 to 28 m/s) using a particle sample with a mean size of 200 μm. A CFD-VOF-DEM model was developed and validated against standard single-particle release into water and application-specific tests of high-speed jet flow. The effect of drag model selection was investigated and the Gidaspow drag model showed optimal results compared to other empirical models. Results of initial experimental work indicated limited jet spread of particle-barren and particle-laden jets. Integrating a capillary force model into the numerical framework ensured constrained jet spread and particle entrainment within the liquid phase. High-speed imaging and surface feature tracking methods provided data that supported the numerical findings. The research offers a practical approach to understanding three-phase jet behaviors with potential implications for optimizing industrial processes involving such flows.

Flow and acoustics in a model rocket flame deflector and deflector cover

The design of a rocket launch environment is a complex process with many different aspects that are highly interconnected. Acoustics, which is one of these, should be investigated in detail due to possible devastating effects on the launch vehicle, crew, and launch environment. This study uses a numerical method to consider a passive noise reduction method applied to a supersonic jet impinging on an inclined flame deflector to decrease the acoustic loads on the launch vehicle and noise levels in the far-field. In a supersonic jet impinging on an inclined flat plate configuration, acoustic waves that travel upstream originate from the impingement and wall jet regions. These upstream traveling waves are a combination of the acoustic waves that are produced by the high speed jet flows in the wall jet region and acoustic waves that reflect from the impingement wall. Due to the inclination of the impingement plate, these waves either travel to the far-field in the upstream direction or travel towards the free-jet region interacting with the high speed flow near the nozzle lip. This interaction can create a self sustaining feedback loop, which can cause acoustic tones to appear in the near- and far-field spectra. It is the aim of the present study to block the upstream traveling waves by introducing a second inclined wall with a circular cut-out between the nozzle exit and the impingement plate. Different configurations with different wall locations and cut-out sizes are investigated using a Detached Eddy Simulation CFD solver and an acoustic solver that is based on the Ffowcs Williams and Hawkings analogy. The mechanisms for the establishment of the feedback loops are examined.

Investigating the Linear Dynamics of the Near-Field of a Turbulent High-Speed Jet Using Dual-Particle Image Velocimetry (PIV) and Dynamic Mode Decomposition (DMD)

The quest for the physical mechanisms underlying turbulent high-speed jet flows is underpinned by the extraction of spatio-temporal coherent structures from their flow fields. Experimental measurements to enable data decomposition need to comprise time-resolved velocity fields with a high-spatial resolution—qualities which current particle image velocimetry hardware are incapable of providing. This paper demonstrates a novel approach that addresses this challenge through the implementation of an experimental high-spatial resolution dual-particle image velocimetry methodology coupled with dynamic mode decomposition. This new approach is exemplified by its application in studying the dynamics of the near-field region of a turbulent high-speed jet, enabling the spatio-temporal structure to be investigated by the identification of the spatial structure of the dominant dynamic modes and their temporal dynamics. The spatial amplification of these modes is compared with that predicted by classical linear stability theory, showing close agreement, which demonstrates the powerful capability of this technique to identify the dominant frequencies and their associated spatial structures in high-speed turbulent flows.

Experimental investigation on high-pressure methane jet characteristic single-hole injector

High-pressure gas direct injection (DI) technology benefits engines with high efficiency and clean emissions, and the gas jet process causes crucial effects especially inside an mm-size space. This study presents an investigation on the high-pressure methane jet characteristics from a single-hole injector by analysing jet performance parameters including jet impact force, gas jet impulse, and jet mass flow rate. The results show that the methane jet exhibited a two-zone behaviour along the jet direction in the spatial dimension induced by high-speed jet flow from the nozzle: zone 1 near the nozzle—the jet impact force and jet impulse increased consistently except for a fluctuation due to shock wave effects induced by the sonic jet and no entrainment occurs, and zone II farther away from the nozzle—the jet impact force and jet impulse became stable when the shock wave effects became weak and the jet impulse was conserved with a linear conservation boundary. The Mach disk height was exactly the turning point of two zones. Moreover, the methane jet parameters, such as the methane jet mass flow rate, jet initial jet impact force, jet impulse, and Reynolds number had a monotonous and linearly increasing correlation with injection pressure.

Flow and surface loading induced by a supersonic jet over an aft deck

Aircraft designs may include an engine that exhausts over the upper fuselage of the aircraft. This design has many benefits including reduced noise below the aircraft. However, the scrubbing of the high-speed turbulent jet flow over the fuselage has the potential to cause structural fatigue. This paper describes a joint experimental/computational study of the surface pressure fluctuations induced by the supersonic jet flow. The model configuration consists of a rectangular convergent-divergent nozzle that exhausts over a flat plate. The plate is a continuation of the lower lip of the nozzle. Pressure measurements are made at several locations on the plate surface. In addition, schlieren visualization is used to identify the jet's shock cell structure. Numerical simulations are performed using Large Eddy Simulation (LES). Results are compared between the simulations and the experiments. The importance of shock turbulent boundary layer interaction to the surface loading is identified.

Transverse Nonuniformity of Air–Water Flow and Lateral Wall Effects in Quasi-Two-Dimensional Hydraulic Jump

Flow field characterization in high-aerated flows often involves flow imaging techniques through transparent sidewalls, and the results may be subject to sidewall effects and thus differ from the central flow behaviors. This paper contributes an experimental investigation of the sidewall effects on the air-water flow distributions in quasi-two-dimensional hydraulic jumps in a rectangular flume. The tested hydraulic jumps are characterized by preaerated approach flows and large inflow Froude numbers from 10.6 to 15.1. The air-water flow properties are measured intrusively along the centerline, sidewall, and transverse cross sections to provide a three-dimensional view of the aerated flow structure. Substantial redistribution of the bubbly flow is observed due to the presence of lateral aeration boundary layers in the high-speed jet-shear region, compared to the less affected free-surface roller. The magnitude difference between the central and lateral air-water flow properties is more distinct in terms of bubble count rate and less evident for void fraction and interfacial velocity, while the affected area is broader for void fraction distributions. The results suggest a concentration of high-speed jet flow in the central bottom flow column, where the jet layer is thicker, the recirculation roller is smaller, and the proportion of small-size bubbles is higher. The width of the central flow region free of the sidewall effects is approximately 60% to 80% of the flume width in the present facility, narrower on the bottom, and broader at the free surface. The findings demonstrate that the transverse variation of air-water flow and the difference between the central and lateral flow fields should not be ignored for the high-speed flow regions of hydraulic jump. A correct assessment of the sidewall effects is essential for interpreting imaging-based measurement of highly-aerated flow.

Analysis of the high-speed jet in a liquid-ring pump ejector using a proper orthogonal decomposition method

ABSTRACT To analyze the complex spatiotemporal evolution law of the high-speed jet flow field in a liquid-ring pump ejector, both the classic and spectral proper orthogonal decomposition (SPOD) methods were introduced to decompose the transient flow field based on the numerical large eddy simulation. The proper orthogonal decomposition (POD) reduced order model (ROM) of the complex flow in the ejector was established to analyze the transient characteristics and reconstruct the flow field. The spatial mode characteristics of density, pressure and vorticity field, and the frequency domain characteristics of mode coefficients were analyzed. The results show that the spatiotemporal decoupling analysis of a high-speed jet flow field can be accomplished by the POD and SPOD methods. A large-scale symmetric coherent structure is formed in the shear layer of the first two modes of vorticity, and a small-scale antisymmetric structure is formed at the trailing edge of the jet flow for the third and fourth modes. This reflects the evolutionary characteristics of the jet shear vortex. There is a significant spatial correlation between the density and pressure modes, reflecting that the evolution of the two structures has important correlation characteristics. The spectral analysis of the mode coefficients shows that the dominant frequencies of 1250 Hz and 18 kHz correspond to the self-excited oscillation frequency of shock waves and the vortex shedding frequency. The POD-ROM can reconstruct the high-speed flow field of the ejector with enough accuracy using the first 30-order modes, and the root mean square error and mean absolute percentage error for the velocity prediction are 0.48% and 0.24%, respectively.

A tip-leakage loss reduction method using a front-loaded blade profile for the high-pressure rotor of a vaneless counter-rotating turbine

To reduce tip-leakage losses, this paper presents a front-loaded blade profile design method for the high-pressure (HP) rotor of a highly loaded vaneless counter-rotating turbine (VCRT). The method is to decrease the blade exit angle and increase the stagger angle with unchanged throat area to obtain front-loaded blade profiles at both the tip-leakage vortex upper and lower boundaries. As the relative exit Mach numbers in the tip region of the VCRT’s HP rotor are all over 1.5, the shearing of the high-speed leakage jet and passage flow near the trailing edge is very strong. To reduce the shearing losses, decreasing the blade exit angle of the HP rotor is adopted to reduce the tip loading near the trailing edge. This means the leakage jet mass-flow rate and speed near the trailing edge are reduced. Hence, the shearing strength and losses of the leakage jet and passage flow near the trailing edge are lower. Since decreasing the blade exit angle of the HP rotor results in increased throat area, increasing the stagger angle is employed to maintain unchanged throat area. Increasing the stagger angle also reduces the tip loading near the trailing edge, leading to reduced high-speed leakage jet mass-flow rate. Thus, the shearing strength and losses of the high-speed leakage jet and passage flow near the trailing edge are further reduced. The efficiency of the HP rotor and VCRT are raised by 0.45% and 0.53% respectively.

Direct numerical simulation of the flow around a sphere immersed in a flat-plate turbulent boundary layer

This study investigates flow past a sphere immersed in a flat-plate turbulent boundary layer by using direct numerical simulations, with the objective of clarifying the effects of a wall-proximity sphere on turbulent coherent structures and turbulence statistics. Three cases are evaluated with gap ratios (G/D) of 0.1, 0.25, and 0.5 at a Reynolds number of ReD=2500, where D is the diameter of the sphere and G is the gap width between the bottom of the sphere and the flat plate. The results show that the wake of the sphere plays an important role in the streamwise region 0<x/D<10. The near-wall streaks break into small-scale point-like or patch-like structures in the near-wake region, with the most significant effect at G/D=0.1. This can be attributed to the interactions between the shedding vortex behind the sphere and vortical structures within the flat-plate boundary layer. Detail analysis of turbulence statistics indicates that the flat-plate boundary layer thickness is increased at x/D<−0.5 owing to the blockage effect of the sphere, whereas it is decreased at x/D>0.5 because of the high-speed jet flow around it. In addition, the presence of a wall-proximity sphere significantly affects the skin friction coefficient. The budgets of the turbulent kinetic energy show that turbulence production and viscous dissipation are augmented due to the formation of small-scale vortices and interactions among them in the near-wake region, especially at G/D=0.1.

Addressing the Impact of Non-intrinsic Uncertainty Sources in the Stability Analysis of a High-Speed Jet

It is acknowledged by mechanical and aeronautical engineers that many important industrial fluid mechanics simulation-based decisions are made by analysing Reynolds-Averaged Navier-Stokes (RANS) simulations. However, despite that the use of RANS simulations has become a necessity, still unrealistic conditions such as not considering experimental variability or blindly trust a turbulence model happens in practice. This is an important concern in simulation of high-speed jet flows, as the reliability and the accuracy of RANS is still an issue. In this work non-intrusive Uncertainty Quantification (UQ) has been applied to the linear stability analysis of 3D RANS simulations of an under-expanded supersonic jet under uncertainty. The Parabolized Stability Equations (PSE) are utilised for the first time in the literature in a probabilistic approach for the propagation of uncertainty upon CFD simulations. As PSE does not include turbulence nor stagnation pressure as parameters in their mathematical formulation (named non-intrinsic parameters in this work), this framework enables a recommended practice to quantify the impact of uncertainty from earlier stages on the latter jet instability analysis. For this objective, an artificial stochastic base-flow is generated from UQ on RANS to develop the final quantification of uncertainties on jet stability characteristics with PSE. Spatial uncertainty quantification results show that the considered stagnation pressure uncertainty (equivalent to mass-flow rate uncertainty) affects mainly to the shock-cells area, which is in agreement with the jet flow mechanics. The tested turbulent viscosity ratio uncertainty from the Spalart-Allmaras turbulence model has been observed more influential on the shear layer region in general, and with a special role on the growth rate of the perturbations. Frequency (in terms of Strouhal number), has been found influential on the spatial localisation of the turbulent wave packets. This procedure is proposed as an standard approach in the field. The framework may help to understand how instability features are being affected by expected or unexpected uncertainty sources and can guide to future robust developments in the industry, for instance in jet noise reduction.

Laser breakdown model in the absorption mode behind a light supported detonation wave

The light supported detonation wave (LSDW) propagation with the laser radiation absorption in a narrow layer behind wave’s front is considered in the paper alternatively to the volumetric energy source model usually used for the energy deposition simulation [1-7]. The next laser plasma flow features were revealed in [8] by methods of numerical simulation:1) laser plasma forms high-speed jet flow behind the LSDW front along the light beam propagation direction,2) jet parameters are close to an isentropic flow mode at significant distances from the LSDW front, therefor can be determined with a good approximation using the unsteady pressure solution for the point explosion model with a kinematic x-t transformation. These features allow one to determine the plasma momentum value (in the direction of a laser beam) of the optical breakdown as an additional factor of effect on gas flow, first indicated in [9]. For an argon flow, we used a comparative analysis of the results of numerical simulations obtained both accounting the absorbed energy only and the breakdown plasma momentum additionally acquired at the absorption of radiation behind the LSDW front.The experimental results of an optical discharge plasma in a subsonic argon flow are also presented. Pulse-periodic radiation with a frequency of 40 kHz and average power of 1.6 kW (peak power more than 30 kW) was generated by CO2-laser created in ITAM SB RAS. In order to obtain the LSDW mode by increasing a length of the breakdown plasma a focusing system f / d ≈ 9 was applied. A high-speed video camera with the exposure time of 1.0 μs, and the shooting speed of 200,000 frames / sec was used to record process. It has been established that the plasma dynamics has two successive stages: from the initial high-speed (of the order of 1 μs) propagation of the optical discharge to the subsequent lower-velocity gas-dynamic stage.

Lagrangian and Eulerian measurements in high-speed jets using Multi-Pulse Shake-The-Box and fine scale reconstruction (VIC#)

Accurate measurement of high-speed flows in the presence of elevated levels of shear and turbulence is a challenging yet necessary endeavor to understand ubiquitous flows that are of great engineering importance. While Eulerian methods, such as Particle Image Velocimetry, represent the traditional approach, Lagrangian alternatives, such as Particle Tracking Velocimetry, have witnessed a resurgence recently due to improved technology and interest in Lagrangian analysis methods. In this research, a recently developed implementation of a volumetric Lagrangian technique for tracking particles in densely seeded flows, namely, Multi-Pulse Shake-The-Box (MP-STB) with the specific implementation referred to as Four-Pulse Shake-The-Box is described and its performance in high-speed jet flows is evaluated. The MP-STB technique is based on recent developments in the Shake-The-Box method by Novara et al. (Experiment in Fluids 60(3):44, 2019) and uses low-speed cameras combined with a double-exposed image acquisition strategy and multi-pulse tracking. Its use of four laser pulses in quick succession with an uneven pulse timing scheme allows for high-accuracy estimates of velocity and acceleration, and repeated ensembles of short-duration, time-resolved measurements in realistic high-speed flows. Experiments with circular jets operating at exit Mach numbers of 0.31 and 0.59 in two different configurations, namely, free jets and jets impinging on a ground plate located 4.75 jet diameters away from the nozzle, were performed to evaluate MP-STB. Scattered four-particle tracks from MP-STB were mapped onto a regular Eulerian grid through the Fine Scale Reconstruction implementation of the VIC# data assimilation method by Jeon et al. (2018). Unique information, including acceleration fields, is presented for these well-known canonical flows. Comparisons with traditional Eulerian measurements from Tomographic PIV, Stereoscopic PIV, and planar PIV are provided to validate the accuracy and comparative cost of volumetric MP-STB measurements combined with the VIC# data assimilation technique.

Windowed Fourier transform and cross-correlation algorithms for molecular tagging velocimetry

Simulated and experimental molecular tagging velocimetry (MTV) images have been analyzed with a technique commonly used to process grid images on surfaces, the windowed Fourier transform with local spectrum analysis (WFT-LSA). A systematic synthetic image study of the modulation transfer function (MTF) and error tendencies of the WFT-LSA was performed and compared with a PIV-style cross-correlation algorithm to see if advanced strategies such as iterative image deformation can improve analysis of gridded images with high noise levels. Testing of single-pass algorithms showed that in typical MTV images, the WFT-LSA yields significantly lower bias errors than cross-correlation (CC) at displacements greater than 1 pixel but slightly higher random error at all displacements and image conditions. Analysis of the MTF shows that CC provided better resolution of spatial fluctuations than the WFT-LSA in many combinations of grid size and interrogation window. Tests of image deformation algorithms showed that the gap in performance between CC and WFT-LSA is maintained even as both methods improve. Additionally, WFT-LSA and CC methods are applied to real MTV experiments in high-speed gas jet flows. A preliminary analysis of phosphorescence lifetime provided by acetone vapor excited at 266 nm is used for assessing the required gas speeds for making MTV application feasible. The application of WFT-LSA to real MTV images demonstrates the ability of the algorithm to handle further real-world effects that could not be considered in the synthetic image analysis, like reduced signal-to-noise ratio and non-uniform intensity of the tagging grid across the image introduced by the actual laser beam energy distribution. With experimental images, CC is more accurate with shear flows but less robust to high noise levels than WFT-LSA, as predicted by the synthetic image analysis.

Gas–solid two-phase flow and erosion calculation of gate valve based on the CFD-DEM model

Gate valves are important pipeline components in pneumatic conveying systems, and they were eroded severely by the impact of solid particles. In this study, the CFD-DEM simulation method was adopted to study the gas–solid two-phase flow characteristics and erosion characteristics of the gate valve. The accuracy of the simulation was validated by comparing the simulation and experimental data. Results show that a high-speed jet flow appears under the flashboard and induces a free shear layer, and the free shear layer attaches at the rear wall of the cavity. Particle distribution shows that the particle number at the upstream of the flashboard increases with decreasing valve opening. The particle number inside the cavity has a similar trend. The erosion results indicate that the number of particles plays an important role in erosion. The range of the erosion gradient region and the maximum erosion rate decrease with increasing particle size. Erosion of the cavity is more serious than that of the flashboard.

A cost-effective production of hydrogen peroxide via improved mass transfer of oxygen for electro-Fenton process using the vertical flow reactor

This study has investigated a novel jet-type reactor (vertical flow reactor) in order to improve the oxygen utilization for enhanced production of hydrogen peroxide (H2O2). In vertical flow electro-Fenton (EF) system, the effects of current density, water flow rate, Fe2+ concentration and initial pH were investigated for the removal of tetracycline hydrochloride. The efficient removal of tetracycline hydrochloride could reach 100% within 60 min under the current density of 24 mA cm−2, water flow rate of 10 L h−1 and pH of 3. The vertical flow reactor was relatively stable and reusable for the removal of pollutants. The removal rates of tetracycline hydrochloride and total organic carbon (TOC) were maintained at about 95% and 80%, respectively in a 5-time continuous runs. Moreover, the vertical flow reactor could efficiently remove a wide type of organic pollutants, and the TOC removals of acid magenta, rhodamine B, alizarin yellow R, orange Ⅳ and diclofenacdium were 75.96, 77.90, 61.27, 72.11 and 82.89%, respectively after 3 h of reaction time. Cathodic adsorption, anodization, and H2O2 oxidation played minor roles in the removal of tetracycline hydrochloride, while the OH radicals are the most pivotal oxidizing substance in the system. As compared with the traditional aeration, the vertical flow reactor has a high-speed jet flow state, which makes the liquid-gas mixture homogeneous, and renders it high oxygen absorption rate, cost effectiveness and high power efficiency for the degradation of pollutants.

Numerical Analysis to the Effect of Guiding Plate on Flow Characteristics in a Ball Valve

When internal flows go through a valve with a small opening degree, high-speed jet flows are induced, which causes the erosion of the valve core and affects the stability of the flow field. Setting guiding plates in the valve behind the valve core has the function of reducing the adverse effect of high-speed jet flows. In this work, numerical simulations were carried out to investigate the effect of the guiding plate on flow and resistance coefficient, velocity and pressure distributions and flow stability downstream of the valve. The number of guiding plates was changed from 0 to 3 and the opening degree was varied from 0 to 100% at intervals of 10%. A guiding plate with holes in it plays the role of bypassing and guiding flow. Under the action of the guiding plate, the flow coefficient obviously decreases, the gap flow between the valve core and the valve wall in the top of the valve are modified, and the gap flow even disappeared in the valve with 3 guiding plates. It was found that setting the guiding plate can improve the performance of the ball valve, reducing the internal erosion and increasing the stability of valve downstream flow efficiently.

Effects of hydrogen direct-injection angle and charge concentration on gasoline-hydrogen blending lean combustion in a Wankel engine

To analyze the effects of hydrogen charge concentration (HCC) and injection angle (IA) on the lean combustion in a gasoline Wankel engine, the present work implemented a numerical simulation model coupling with the kinetic mechanisms and validated with the experimental data. Results found that with the increase in HCC, the penetration of hydrogen injection is enlarged and the area of the high-speed jet flow is expanded. The jet-flow area for IAs of 45° or 135° is larger than that of 90°. Changing IA could obtain the hydrogen distribution at different regions of the rotor chamber and IA of 90° acquires the smallest hydrogen-rich region. Increasing IA brings about the reduced flame speed substantially; the flame area for IAs of 45° and 90° expands with the increment of HCC whereas the contrary pattern is witnessed at the IA of 135°. Smaller IA leads to the major burning occurring untimely, which resulting in less work delivery of the engine. The hydrogen consumption for IAs of 45° and 90° increases as HCC is ascendant while that for IA of 135° is just the reverse. Variations in the mixture distribution and turbulence are the intrinsic mechanism of how the HCC and IA reflects the combustion progress. As hydrogen is injected with larger HCC and smaller IA, a relatively richer mixture and higher turbulent kinetic energy are distributed close in the spark ignition region. The peak combustion pressure reduces and its corresponding crank position delays with the widened IA at any HCC. Considering the fuel combustion and nitric oxide formation, as hydrogen volume fraction is 3% and IA is 45°, the engine could realize the optimized performance under the computational condition. An efficient combustion performance may be performed in engineering application if the hydrogen IA is in accordance with the rotor rotating direction at lower HCC.