High Turbulent Kinetic Energy Research Articles

Flow Analysis of Central Venous Outflow Tract: A New Approach to Understanding Pulse-Synchronous Tinnitus.

Pulse-synchronous tinnitus (PST) has been linked to multiple anatomical variants of the central venous outflow tract (CVOT) including sigmoid sinus (SS) dehiscence and diverticulum. This study investigates flow turbulence, pressure, and wall shear stress along the CVOT and proposes a mechanism that results in SS dehiscence and PST. Case series. Tertiary Academic Center. Venous models were reconstructed from computed tomography scans of 3 patients with unilateral PST. Two models for each patient are obtained: a symptomatic and contralateral asymptomatic side. A turbulent model-enabled commercial flow solver was used to simulate the pulsatile blood flow over the cardiac cycle through the models. Fluid flow through the transverse and SS junction was analyzed to observe the velocity, pressure, turbulent kinetic energy (TKE), and shear stress over a simulated cardiac cycle. Fluid flow on the symptomatic side showed increased vorticity in the presence of an SS diverticulum. Higher TKE with periodicity following the cardiac cycle was observed on the symptomatic side, and a sharp increase was observed if SS diverticulum was present. Shear stress was highest near the narrowest segments of the vessel. Pressure was observed to be lower on the symptomatic side at the transverse-SS junction for all 3 patients. Computational fluid dynamics modeling of blood flow through the CVOT in PST suggests that low pressure may be the cause of dehiscence, and tinnitus may result from periodic increases in TKE.

Flow Analysis of Central Venous Outflow Tract: A New Approach to Understanding Pulse-Synchronous Tinnitus.

Pulse-synchronous tinnitus (PST) has been linked to multiple anatomical variants of the central venous outflow tract (CVOT) including sigmoid sinus (SS) dehiscence and diverticulum. This study investigates flow turbulence, pressure, and wall shear stress along the CVOT and proposes a mechanism that results in SS dehiscence and PST. Case series. Tertiary Academic Center. Venous models were reconstructed from computed tomography scans of 3 patients with unilateral PST. Two models for each patient are obtained: a symptomatic and contralateral asymptomatic side. A turbulent model-enabled commercial flow solver was used to simulate the pulsatile blood flow over the cardiac cycle through the models. Fluid flow through the transverse and SS junction was analyzed to observe the velocity, pressure, turbulent kinetic energy (TKE), and shear stress over a simulated cardiac cycle. Fluid flow on the symptomatic side showed increased vorticity in the presence of an SS diverticulum. Higher TKE with periodicity following the cardiac cycle was observed on the symptomatic side, and a sharp increase was observed if SS diverticulum was present. Shear stress was highest near the narrowest segments of the vessel. Pressure was observed to be lower on the symptomatic side at the transverse-SS junction for all 3 patients. Computational fluid dynamics modeling of blood flow through the CVOT in PST suggests that low pressure may be the cause of dehiscence, and tinnitus may result from periodic increases in TKE.

Insights into turbulent flow structure and energy dissipation in centrifugal pumps: A study utilizing time-resolved particle image velocimetry and proper orthogonal decomposition

The purpose of the study is to investigate the flow structure and energy dissipation mechanism within centrifugal pump impellers. The velocity fields at the mid-sections of the flow passages of 4- and 5-blade impellers were measured under various flow rates using the Time-resolved Particle Image Velocimetry (TR-PIV) technique; the proper orthogonal decomposition (POD) analysis was performed to extract flow structures with different scales; the dissipation rate was estimated using the large-eddy PIV method; the correlation between turbulent kinetic energy (TKE) and dissipation rate was measured using the cross-correlation analysis. The findings are as follows: impeller with more uniform and stable flow, the scale and energy contribution of large-scale structures in lower order modes are smaller, leading to higher impeller efficiency; large-scale structures identified in the low-order modes correspond to locations of high TKE and dissipation areas; the high velocity gradients within the impeller passage and the interactions between large-scale flow structures encourage the breakup of large-scale turbulent structures into dissipative-scale structures; the correlation between TKE and dissipation rate reflects the extent to which large-scale flow structures within the impeller passage break up into dissipative scales.

Optical and numerical study on the effect of wall impingement on passive jet ignition characteristics of methane/air mixture

Pre-chamber turbulent jet ignition is a promising high-efficiency combustion technique to achieve stable lean-burn operation for spark-ignition engines. Wall impingement by a high momentum turbulent jet could exert a critical influence on jet ignition behavior. In this work, the passive jet ignition characteristics of premixed methane/air mixture under wall impinging condition was investigated based on optical experiments in a constant volume chamber and numerical simulations. Two ignition modes were found for flat wall impinging cases across a range of non-dimensional impinging distances (H/D) from 5.7 to 20. In mode 1, ignition initiates from near wall region. Under lean conditions of λ = 1.3, compared with that in the free jet case, the ignition delay time characterized by a 5 % mass fraction burned (MFB-05), decreases by 3.3 ms at H = 30 mm and increases by up to 6.6 ms at H = 20 mm. In mode 2, ignition initiates from the jet root. The ignition delay times are shorter for all impinging distances (H = 20, 30, 40 mm), with MFB-05 decreasing by up to 3.4 ms. Simulations reveal that when the wall is located in the jet developing zone with H/D below 7, wall impinging deteriorates the ignition, which is attributed by higher turbulent kinetic energy (TKE) and lower Damköhler (Da) number near the stagnation zone, resulting in extended ignition delay. Conversely, as H/D increases, ignition is promoted by the stagnation effect with a shorter ignition delay. Additionally, the effect of wall shapes was analyzed. Using sharp-tip V-shaped wall, the stagnation region with high TKE is minimized. A blunt-tip V-shaped wall shows enhanced impinging but no obvious increase of Da number at stagnation point. Using M-shaped wall, the ignition mode with a “lift-off” flame was found. Besides, ignition is more favorable in the secondary jet zone with active radicals and higher Da number.

Flow stirred by open turbine: A modal analysis of multiscale flow characteristics

AbstractThe turbulence observed in the stirred tank is a result of the superposition of flows at different scales, each exerting various influences on the operational processes. To understand the flow characteristics associated with stirring, this paper undertakes particle image velocimetry (PIV) experimental research on an unbaffled tank stirred by an open turbine featuring four distinct blade deflection angles. The flow field in the unbaffled tank manifests as a double‐circulation flow pattern; however, it is worth noting that the blade deflection angle exerts a significant impact on the stirring process. Specifically, when the blade deflection angle reached 90°, the flow discharge aligned closely with the radial direction, accompanied by pronounced fluctuations in the high‐velocity region. The Lagrangian coherent structures (LCS) formed were subsequently extracted and subjected to finite‐time Lyapunov exponent (FTLE) analysis. Notably, a more regular wake pattern emerged in proximity to the blade tip, while a larger scale flow structure persisted along the flow direction. To systematically analyze the flow field stirred by the open turbine, modal analysis was employed. By reconstructing the flow field based on the principle of 50% energy content, the decomposition of flows at different scales was achieved. The turbulent kinetic energy (TKE) generated by the various scale flows was subsequently calculated, revealing that the high TKE values primarily originate from the large‐scale flow structure. Conversely, the TKE generated by the small‐scale flow exhibits a uniform distribution across different regions. Notably, in regions characterized by higher velocities, the peak TKE associated with the small‐scale flow also manifests; however, it is significantly smaller in magnitude compared to that generated by the original flow or the large‐scale flow.

Swimming behaviour of Atlantic salmon kelts migrating past a hydropower plant dam: Effects of hydraulics and dam operations

Hydropower plants commonly impede the downstream migration of Atlantic salmon (Salmo salar) kelts. Thus, understanding the effects of hydraulic conditions on kelt behaviour and passage performance at dams is crucial for developing effective mitigation measures. In this study, we investigated the influence of hydraulic conditions on kelt passage performance and swimming behaviour at a Norwegian hydropower plant. We combined biological data from 48 kelts collected via acoustic telemetry with hydraulic data modelled using computational fluid dynamics. We assessed kelt passage performance using metrics such as time-to-pass, total number of detections, and total number of detections per day. Additionally, we analysed swimming depths and speeds in relation to the hydraulic conditions created by different dam operating conditions. We found that the dam operation schedule impacted the kelts' ability to find a route past the dam. Though kelts could have passed the dam throughout the study period via a submerged pipe at the dam (which had seemingly sufficient discharge for the kelts to find), 98 % of the kelts instead waited for a spill gate to open partway through the study period. The swimming depth analysis indicated diel variation, with kelts swimming nearer to the water surface during the night. We found that swimming speed increased with increasing kelt body length, particularly under high turbulence kinetic energy and during the day. Furthermore, kelts swam faster as water velocity increased, but slowed down again as turbulence intensity increased. Our findings reveal the effects of hydraulic conditions and dam operations on the migration behaviour of Atlantic salmon kelts. This provides valuable insights for developing strategies to optimise dam operations and improve fish passage performance, including the need to spill enough water to increase passage success and will contribute to sustainable management of Atlantic salmon populations in regulated rivers.

Numerical Investigations of Outer-Layer Turbulent Boundary Layer Control for Drag Reduction Through Micro Fluidic-Jet Actuators

Drag reduction through turbulent boundary layer control (TBLC) is an essential way to develop green aviation technologies. Compared with traditional approaches for drag reduction, turbulence drag reduction is a relatively new technology, particularly for skin friction drag reduction, and it is becoming a hotspot problem worldwide. This paper focuses on the research of micro fluidic-jet actuators used for outer-layer boundary layer control with high-performance computing (HPC). This study aims to reduce turbulent drag by reshaping the flow structure within the turbulent boundary layer. To ensure the calculation accuracy of the core region and reduce the consumption of computing resources, a zonal LES/RANS strategy and WMLES method are proposed to simulate the effects of fluidic-actuators for outer-layer boundary control, in which high-performance computing has to be involved. The studies are performed on the classical zero-gradient turbulent flat plate cases, in which three different control strategies named “W-control,” “V-control,” and “VW-control” are used and compared to study the effects of drag reduction under a low Reynolds number at Reτ = 470 and a higher Reynolds number at Reτ = 4700. The mechanism for drag reduction is analysed via a pre-multiplied spectral method and a parallel dynamic mode decomposition (DMD) method. The results show that the present approach can effectively simulate the outer-layer turbulent boundary control where the “V-control” with the fluidic-jet actuator array behaves well to achieve an average drag reduction (DR) rate of more than 5% for the high Reynolds number case of the flat plate boundary layer. The high Reynolds shear stress and turbulent kinetic energy distribution in the boundary layer region show an obvious uplift under the effects of actuators, which is the main mechanism for drag reduction.

Effects of vegetation density on flow, mass exchange and sediment transport in lateral cavities

Large-Eddy Simulations (LES) were used to investigate the hydrodynamics and mass transfer between the flow in the main channel and a vegetated lateral cavity. Fourteen vegetation densities (0 to 10.65 %) were tested, revealing two distinct hydrodynamic patterns. For cavities with low vegetation density (a < 3.99 %), one primary gyre in contact with the interface between main channel and cavity with high velocity was formed; the thickness of the mixing layer grew longitudinally along the interface, and regions with high vorticity and turbulence kinetic energy appeared at the interface and inside the cavity. For cavities with high vegetation density (a > 3.99 %), two gyres in contact with the interface with low velocity were formed, the thickness of the mixing layer did not grow, and the vorticity and turbulence kinetic energy were low inside the cavity. The mass transport presented the same threshold value as the hydrodynamics (a = 3.99 %). For cavities with low vegetation density, a fast mass transfer occurred through the interface between the main channel and cavity and inside the cavity, while the opposite was observed for cavities with high vegetation density. Finally, the modelled hydrodynamics was used to infer possible sediment deposition patterns and flow resistance.

Numerical investigation the shape of groove on tip leakage vortex suppression of a NACA0009 hydrofoil

To investigate the effect of different bionic grooves on the tip leakage vortex, four bionic grooves with different shapes were designed, which are semicircular, rectangular, triangular and trapezoid. The streamline, pressure, vortex strength and turbulence kinetic energy were analyzed to clarify the suppression mechanism. When the groove is arranged, the velocity of vortex center and the area of high-intensity vortex area decrease. The vortex strength in the triangular groove is higher than other groove shapes. The pressure in the center of the tip leakage vortex core increases. The low pressure area reduces obviously, which is the smallest in the trapezoidal groove condition. The turbulent kinetic energy in the main flow field increases, but decreases in the tip clearance. The high turbulent kinetic energy region is divided into small pieces by the bionic groove, which is the smallest in the rectangular groove condition. The bionic groove leads to the decrease in lift-to-drag ratio, which is the largest in the semicircular groove and smallest in the rectangular groove condition.

The airflow characteristics and thermal comfort evaluation in high-speed train cabin with mixing ventilation: An experimental and numerical study

The airflow characteristics and distribution in high-speed train (HST) cabins have been of great significance for the travel comfort of passengers, while the indoor dynamic airflow characteristics and overall thermal comfort are still unclear. This study first conducted a transient experiment in a real train cabin with the mixing ventilation mode. Measurements showed that the turbulence intensity of the whole airflow is between 20% and 60%. The center zone airflow has a higher turbulence kinetic energy, while the spectral characteristics are closer to the natural wind with the β value between 1.2 and 1.8. Moreover, considering the limitations of the experiment, a corresponding numerical study was carried out. To be closer to the actual situation, the numerical simulation adopted a partitioned heat transfer wall setting, the average deviation of the airflow velocity and temperature from the experimental comparison was 0.057 m/s and 0.25 °C, respectively. Numerical results revealed two vortices in the seating area, a significant longitudinal airflow and an increasing temperature near the carriage ends. Then, to further analyze the compartment's thermal environment and the acceptance of airflow, thermal comfort indicators based on the airflow parameters were used. The predicted mean vote (PMV) showed the thermal comfort of the cabin is slightly cold. Predicted percentage dissatisfaction (PPD) and draught rate (DR) in the center area are barely satisfactory, more than 25% and 20%, respectively. The results of this study can provide an essential reference for the optimization design of ventilation systems in public transport.

THERMAL AND HYDRODYNAMIC ANALYSIS OF NANOFLUID FLOW IN A CIRCULAR PIPE USING EULER-GRANULAR MIXTURE MODEL

THERMAL AND HYDRODYNAMIC ANALYSIS OF NANOFLUID FLOW IN A CIRCULAR PIPE USING EULER-GRANULAR MIXTURE MODEL

Vortex dynamics characteristics in the tip region based on Wray–Agarwal model

In order to solve the blockage effect and energy dissipation phenomenon caused by cavitation in the low-pressure vortex core region, this paper analyzes the spatial evolution of vorticity intensity and turbulent kinetic energy intensity under different cavitation conditions based on the Wray–Agarwal (WA) model. First, the tip leakage flow characteristics are studied, the evolution of vorticity and vorticity intensity is analyzed, then the distribution of turbulent kinetic energy distribution in the blade tip region is studied, and finally, the vorticity transport characteristics of the tip region are analyzed. It is found that the tip leakage rate is less affected by the vortex cavitation of the tip leakage, and there is a strong interaction between the leakage flow at the tip leading edge and the trailing edge, and the separation vortices and low-speed regions formed in the end-wall region cause blockage of the flow passage. Low pressure causes cavitation to cover most regions of the suction surface, inhibiting the formation and development of the tip leakage vortices. The distribution range of high turbulent kinetic energy region is almost the same as that of high-vorticity region, and there is a positive correlation between the two intensities. Severe cavitation causes the high turbulent kinetic energy region at the outlet of the flow passage to develop in the radial and axial directions of the impeller, which increases the turbulent dissipation and energy loss. The change of vorticity transport intensity caused by cavitation is mainly reflected in the expansion contraction term, and the Coriolis force term plays a dominant role in the vorticity transport process. This paper provides a reference for further improving the performance of mixed-flow pumps.

Experimental Study of the Thermal Management System of an Air-Cooled Li-Ion Battery Pack with Triangular Spoilers

Abstract This research experimentally examines the thermal behavior of an air-cooled Li-ion battery pack with triangular spoilers. The objective is to enhance temperature uniformity and reduce the maximum temperature of the battery pack by redirecting airflow toward regions of higher temperatures using triangular spoilers. The effects of spoiler angles (α) and spoiler positions (Ds) on the thermal performance of a 24V, 10Ah aligned battery pack are investigated. The parameters used to evaluate the thermal performance are temperature variation along as well as transverse to the airflow direction and temperature variation around the circumference of the cell. The maximum temperature (Tmax), average temperature (Tavg.), maximum temperature difference (ΔTmax), and standard deviation of the temperature (σT) are the other performance parameters that are assessed. It is observed that the temperature of the battery pack decreases along the airflow direction with both the increase in α and Ds. It happens due to the enhancement in the heat transfer rate caused by higher turbulence kinetic energy. The non-uniformity in the cell temperature around the circumference improves by 0.4 K and 1.8 K with the change in α and Ds, respectively. It is found that Tmax and Tavg of the battery pack are reduced by a maximum value of 2.5 K and 1.55 K, respectively, compared to the case when no spoiler is used. The maximum reduction in ΔTmax and σT is found to be 2.4 K and 1.02, respectively.

Comparisons of Overall Performance Among Double-Jet Film Cooling Holes, Cylinder Holes, and Fan-Shaped Holes

Abstract In this paper, the film-cooling effectiveness (η) and heat transfer coefficient (h) of different film hole geometries are investigated, including double-jet film cooling (DJFC) holes, streamwise cylindrical holes, and fan-shaped holes, both experimentally and numerically. Results reveal that when the blowing ratio is less than 1.0, the DJFC holes have the highest η and the highest h, as well as the highest net heat flux reduction (NHFR). However, a higher blowing ratio (&amp;gt;1.0) leads to a quickly decreasing NHFR of DJFC holes. The asymmetric antikidney vortex and the high turbulent kinetic energy (TKE) are dominant in the performance of the DJFC holes. Owing to medium effectiveness and the lowest heat transfer coefficient, the fan-shaped holes possess the highest net heat flux reduction at M = 2.0 although the value is negative. The relatively weak kidney vortex and the low TKE can explain the phenomena. The cylindrical holes have the lowest η and the lowest NHFR due to the kidney vortex and relatively higher TKE.

Large eddy simulation of enhanced heat transfer in grooved channel with pulsating flow corresponding to hydrodynamic frequency

This paper presents a numerical investigation on flow and heat transfer in a grooved channel formed by 9 rectangular blocks with steady and pulsating flow. Large eddy simulation is used to simulate the hydrodynamic instability in steady flow and heat transfer enhancement for pulsating flow. The simulations for steady flow at Re=700, 1500, 2500, are firstly conducted, showing that there are 23Hz, 70Hz and 130Hz natural frequencies fN induced by hydrodynamic instability (corresponding to Strouhal number StN=0.876, 1.243, 1.385) behind the first block, which disappear quickly with the flow development. A natural frequency fN of 34Hz (StN=1.295) is found only at Re=700 and it can be maintained and amplified by groove structures. Subsequently, a sinusoidal pulsating flow is applied, with the forcing frequency StF equal to the natural frequency StN in steady flow and the dimensionless amplitude A fixed at 0.2. Flow and thermal performance of the grooved channel is studied under the pulsating condition. A periodic process of vortex generation-shedding-fusion is found behind each block and the fluid in the channel has higher turbulent kinetic energy than that under the steady condition. Ultimately, compared with the thermal and pressure-drop performance between steady and pulsating flow, the enhancement of time-average Nusselt number ranges from 48.08%, 15.64%, 8.61% and time-average friction factor increases by about 40% at Re=700, 1500, 2500. The thermal performance factor is increased by 30.96% and 4.20% at Re=700, 1500 but is reduced slightly by 3.48% at Re=2500. It indicates that the augmentation of heat transfer through pulsating flow is significant at low Reynolds numbers.

Investigation on corrosion tendency behaviour of TA2 titanium alloy welded joints under flow scouring conditions using the array electrode method

PurposeThe corrosion behaviour of titanium alloy surface when fluid with different flow rates flows through welded joints with different residual heights was explored.Design/methodology/approachThe experiment uses a combination of array electrodes and simulation.FindingsIt is found that when the weld reinforcement exists, the corrosion tendency of both ends of the weld metal is greater than that of other parts of the welded joint due to the influence of high turbulence kinetic energy and shear stress. The presence of weld reinforcement heights makes the fluid behind it fluctuate greatly. The passivation films of both the base metal (BM) at the rear and the heat-affected zone (HAZ) are more prone to corrosion than those of the front BM and HAZ, and the passivation film is rougher.Originality/valueThe combination of test and simulation was used to explore the influence of electrochemical and hydrodynamic factors on the corrosion behaviour of titanium alloy-welded joints when welding residual height existed.

Experimental study of the behavioral response of fish to changes in hydrodynamic indicators in a near-natural environment

The large-scale construction of hydropower projects has significantly altered the ecohydrological conditions of fish habitats, and habitat, migration and other behavior of fish have been affected to varying degrees. Although the behavioral characteristics of fish under different hydrodynamic conditions have been investigated in a number of indoor experiments, it is still difficult to apply the results of hydrodynamic indicators directly to the practice of ecological restoration. In order to investigate the response relationship between fish behavior and hydrodynamic indicators under near-natural conditions, and to clarify the structural linkage of multiple influences between the external ecological environment, external behavior and internal changes of fish, the study relies on a large ecological test site in which the flow rate of the rivers can be changed. A low-frequency radio identification device was used in several monitoring sections in the test river to monitor the behavioral trajectories of fish in real time. The study shows that the method of fish behavior tracking based on passive integrated transponder (PIT) tags is feasible in small near-natural rivers. The test fish were more active under a low flow rate and changed their upstream trajectory in response to flow changes. When the flow velocity reached 1.6–1.8 m/s, the fish upstream gradually shifted from along the mainstream direction to along the shoreline. There was no significant difference in the activity of the test fish between day and night, with fish preferring to inhabit areas of low flow velocity and low turbulent kinetic energy. There was a range of high flow velocities (1.6–1.8 m/s) and high turbulent kinetic energy (0.1–0.15 m2/s2) that stimulated the swimming behavior of the fish. In addition, the physical indicators and physiological and biochemical indicators of fish were also included in the research scope. The test fish with high activity were slender after long-term swimming training, and their hemoglobin concentration and red blood cell number were higher than those of inactive fish and cultured fish. The research results will be used to optimize river restoration projects, promote the recovery of fish resources and population size, and reduce the negative impact of hydropower projects on the ecological environment.

Visualization research of energy dissipation in a pump turbine unit during turbine mode's starting up

Identifying the precise location of flow energy dissipation (FED) in pump turbines is crucial for enhancing the stability of pumped storage power stations. In this study, the transient process of the turbine mode's starting up in the pump-turbine has been simulated to examine the FED locations by using the one-dimensional and three-dimensional (1D-3D) coupled computational fluid dynamics (CFD) method. This analysis pinpoints high FED locations in each component of the pump-turbine. The observations reveals that the trailing edge of the guide vane consistently demonstrates high FED values, while wall shear stress, axial and radial forces had a significant effect on flow characteristics. Moreover, high FED sites correspond to high turbulence kinetic energy locations. Continuous wavelet transform (CWT) has been applied to examine the time-frequency characteristics during this process. Low frequency (fc = 0.12) has been identified as the dominant frequency in the volute. In the draft tube, the wavelet magnitude of the double blade passing frequency (fc = 18) is 30.4% of that under the dominant frequency (fc = 9). Regional visualization of FED offers a valuable method for the in-depth understanding of energy dissipation in pump turbines and improving operational stability in pumped storage power stations.

Numerical study of the effects of excess air ratio on passive pre-chamber jet performance and ignition mechanism

Pre-chamber (PC) ignition is a promising lean-burn technology to improve the efficiency of spark ignition (SI) engines while achieving ultra-low NOx emissions. However, the significant effects of the excess air ratio (λ) on the PC jet performance and ignition mechanism were still not fully unraveled. The current study numerically investigated the jet characteristics and combustion behaviors of a narrow-throat PC with two rows of orifices on a passive PC engine fueled with methane. The numerical model was validated extensively by the pressure, heat release rate, and natural flame luminosity (NFL) imaging of the PC flame jet. A detailed comparison of the NFL images of the jets and the simulated flame iso-faces presented excellent matching in the flame jet penetration and propagation process. The results reveal that the λ = 0.9 case has the best jet performance, but it doesn’t lead in every jet characteristic. For instance, the jet temperature is highest under λ = 1.0, and OH concentration is most under λ = 1.1. The transition from cold jet to flame jet produces noticeable jet non-uniformity, which is reported for the first time. This observation can be remarked as a more accurate indication of the initiation of pre-chamber flame jet discharge. The asymmetrical mixture inflow from the main chamber produces asymmetrical turbulent kinetic energy (TKE) and temperature distributions; these result in different flame propagation in the PC, jet non-uniformity, and varied stages of jet discharge. The upper jets are quenched in every case because of the much higher TKE, while the lower jets don’t present quenching when the λ ranges from 0.9 to 1.3; especially, the λ = 1.1 case has the best ignition performance for its most OH radicals. The “jet ignition regime”, in which flame quenching takes place, results in highly non-uniform flame propagation and low flame propagation speed. The ultra-rich case shows more signs of jet ignition and thus exhibits worse jet performance than the lean cases. This study uncovers the mechanisms and the optimal λ value for the pre-chamber ignition of the main chamber charge, providing valuable guidance for PC design.

Multi-objective optimisation of K-shape notch multi-way spool valve using CFD analysis, discharge area parameter model, and NSGA-II algorithm

Multi-way spool valves (MWSVs) with K-shape notches (KSNs) provide advantages such as improvement of the actuator speed control, micro-action, and response performance. However, the pressure drop (PD) associated with the energy consumption is larger of MWSVs under the high-pressure and large-flow condition. Meanwhile, extremely complex flow coefficient and multi-parameter, highly coupled KSNs are the chief factors restricting the flow-pressure characteristics exploration and optimisation design of MWSVs. To address these problems, complete numerical research and experiment are performed in this study, especially concerning the method of MWSV flow-pressure characteristics modelling, and surrogated model-based optimal design of KSN structures. First, the relationships between KSN structure parameters and flow-pressure properties of MWSV are modelled on the innovative discharge area parameter model (DAPM) and response surface methodology (RSM) (RSM-DPAM) using the CFD dataset. Second, to reduce the PD combining the flow control performance, surrogate model-based optimisation design is addressed. During optimisation, six KSN structure parameters are chosen as design variables, PD and flow area relative deviation (FARD) are selected as objective functions, and the RSM is employed as the projected model. Depended on the created surrogate model, the non-dominated sorting genetic algorithm (NSGA-II) is established to search for the optimal KSN structure. To certify the performance of the optimisation, flow field characteristics are analysed. The results demonstrate that the proposed RSM-DAPM-RSM model achieves reliable prediction for PD and FARD with a great correlation coefficient (0.9757 and 0.9946). The average PD reduces as much as 7.23% while the FARD is only 1.28%. Moreover, the region of low-pressure, high-velocity, and high-turbulent kinetic energy in the flow field are reduced. The proposed framework enhances the performance in KSN spool optimisation and could be applied to other kinds of notches.Abbreviations: BOI: Body of influence; BSV: Bucket spool valve; CFD: Computational fluid dynamics; CM: Construction machinery; DAPM: Discharge area parameter model; FARD: Flow area relative deviation; FCC: Flow control characteristic; GSA: Global sensitivity analysis; KSN: K-shape notch; MHAs: Meta-heuristic algorithms; MODE: Multi-objective differential evolution; MOGA: Multi-objective genetic algorithm; MOO: Multi-objective optimisation; MOPSO: Multi-objective particle swarm optimisation; MWSV: Multi-way spool valve; NRMS: Non-road mobile source; NSGA-II: Non-dominated sorting genetic algorithm; OLHD: Optimal Latin hypercube design; PD: Pressure drop; PDCs: Pressure drop characteristics; RSM: Response surface methodology; SA: Sensitivity analysis; TKE: Turbulent kinetic energy; TOPSIS: Technique for order preference by similarity to ideal solution; VFR: Volume flow rate