Numerical Experimental Methods Research Articles

Analysis of flow and energy dissipation in pump turbine with small guide vane opening

In this study, a detailed flow state analysis of a reversible pump turbine (RPT) under small guide vane opening conditions was conducted using both numerical simulation and experimental methods on three analysis planes at 0.5 span. The entropy production rate (EPR) in entropy production theory was utilized to visualize the location and magnitude of energy losses in the flow process. The focus was placed on the coherent vortex structures in the volute, stay vane, guide vane, and runner flow path. The results demonstrate that, throughout the runner’s cycle, the leading edge of the guide vane experiences low-pressure regions with uneven pressure distribution within the runner channel. Velocity streamlines reveal flow separation and vortex generation at the typical guide vane trailing edge, with a maximum velocity reaching 49.7. Analysis of radial force and torque on typical guide vanes and the runner indicates that radial force and torque on the guide vanes do not significantly change, with the radial force coefficient CF r−x varying between 0.254 and 1.3. Major energy losses are concentrated behind the trailing edge of the guide vane, primarily in the form of jet wake. Coherent vortex structures are observed in the volute, stay vane, guide vane, and runner flow path, with slight turbulent wake at the trailing edge of the stay vane, clear shedding vortex streets, and vortex build-up in the bladeless area between the guide vane and the runner.

Insights into the relationship between particulate flow characteristics and local erosion behaviour under waterjet: The role of particle-fluid-surface interaction

In this study, the erosion characteristics of eutectic high entropy alloy under the liquid–solid two-phase flow is investigated by a coupled numerical-experimental method, in order to reveal the intrinsic relationship between microscopic erosion mechanism (experimental test) and the related particle-fluid-surface interaction (CFD modelling). Furthermore, instead of the common relation between average erosion rate and mainstream flow velocity, the relationship between local erosion distribution and local particulate flow characteristics is clarified. The erosion rate and erosion pattern match well between the experiment and simulation. The results demonstrate that NiCoCrFeNb0.45 exhibits superior anti-erosion performance when compared to other widely used equipment metals. The erosion profile agrees well with the shape of surface velocity distribution, indicating a close relationship between surface erosion behaviour and flow characteristics. In particular, the erosion pattern at a normal angle appears as a symmetric ring due to the flow stagnation phenomenon, with slight erosion damage in the centre area and severe erosion in the surrounding, whereas the erosion profile at an oblique angle displays an elliptic shape, with severe erosion damage in centre. Notably, the primary erosion mechanism varies dramatically in different surface regions, induced by the various impact velocities and angles associated with the corresponding changes in the flow field. This study provides a deeper understanding of erosion behaviour in terms of the interrelationship among the material mechanical properties, particulate flow field and particle-surface impingement behaviour.

Numerical and experimental study of the combustion performance of an integrated inclined combustor

To shorten the length of an aero-engine combustor and reduce its weight, we propose an integrated inclined combustor. A combination of numerical calculations and experimental research methods is employed to conduct relevant research on the cold and combustion flow fields and ignition dynamic processes of the integrated inclined combustor. Results show that the inclination angle of the swirler has minimal effect on the total pressure loss and combustion efficiency of the integrated inclined combustor. However, as the swirler’s inclination angle increases, the uniformity of the outlet temperature distribution and recirculation flow rate of the primary combustion zone decrease. Furthermore, when the integrated inclined combustor is ignited, the flame does not propagate symmetrically to both sides in the circumferential direction but propagates faster along the inclination direction of the swirler.

Numerical and experimental study on manifold-distributed jet microchannel with micro-pin-fins

Traditional parallel microchannels are inadequate for managing the thermal requirements of newer, large-area and high-heat-flux chips. This inadequacy arises from its high flow resistance and poor temperature uniformity. Therefore, A novel manifold microchannel heat sink combining manifold inlet/outlet structures, distributed array jets, and micro pin-fins is introduced. Numerical simulations and experimental methods were employed to investigate the flow and heat transfer performance of the heat sink. Experimental results show that, with an average heat flux density exceeding 330 W/cm2 and a total power of 2500 W, the average chip temperature remains below 70 °C, ensuring efficient heat dissipation. Secondary impingement occurs at sufficiently low jet chamber heights, resulting in an increase of 3 times in the average Nusselt number for a smooth base plate. For the micro-pin-finned surface, it is shown that the presence of micro-pin-fins is not necessarily conducive to heat transfer enhancement. A critical volume fraction of micro-pin-fins (critical fin-ratio) exists where the obstructive effect and enhancement effect balance each other out. This value is influenced by multiple parameters. Finally, a novel relationship for predicting the average Nusselt number of jet impingement was proposed, with an average absolute error of less than 15 %. This series of investigations addresses the existing gaps in research on manifold-distributed array jet heat sinks and provides a meticulous theoretical foundation for the design and optimization of heat sinks facing the high-power chips.

Solid-liquid flow characteristics of twin-screw pump under solid-containing transportation

Abstract Twin-screw pumps have the wear risk when the fluid contains particles. In order to clarify the flow characteristics of the twin-screw pump under solid-containing transportation, the solid-liquid flow characteristics research on a twin-screw pump are carried out using numerical simulation and experimental methods in this paper. The results show that the particle concentration has a small effect on the volumetric efficiency and hydraulic efficiency of the twin-screw pump under each differential pressure, but the presence of particles could increase the volumetric efficiency limitedly. The velocity of main flow and the turbulent kinetic energy have been restrained by the particles in the tooth chamber, and the inhibition phenomenon is more significant with the increase of particle concentration. The particles in the tooth chamber are inhaled by the leakage flow at the tooth-tip clearance. Some particles hit the tooth-tip and cause the abrasion, others flow into the tip clearances, which decreases the leakage flow velocity and results in a higher volumetric efficiency than that of the pure-liquid condition. The results of the study will provide a theoretical basis for the study of solid-containing transportation and particle wear in twin-screw pumps.

Establishment of ductile fracture locus of 2219 aluminum alloy at cryogenic temperature

Abstract Cryogenic forming has been used to manufacture intricate curved surface aluminum components. The special geometry and mold constraints cause the stress state to continuously evolve. Coupling with the cryogenic temperature makes the deformation process more complicated. Especially for the final fracture, which greatly determines the forming quality of the components. Thus, the cryogenic fracture behavior of three typical stress states was obtained by conducting tensile experiments. Fracture strains and stress paths were obtained using a hybrid numerical-experimental method. Finally, the cryogenic fracture locus was obtained based on the MMC ductile fracture criterion. The results indicate that the AA2219-O exhibits superior ductile fracture properties at cryogenic temperature. The fracture strain of AA2219-O was increased by 52.6% at the uniaxial tensile stress state, and by up to 80.0% at under plane strain stress state. This research has a guiding significance for cryogenic forming.

Modeling state-of-charge dependent mechanical response of lithium-ion batteries with volume expansion

The behavior of lithium-ion batteries under mechanical abuse conditions has been studied extensively in recent years. Typically, characterization is performed by conducting experiments on discharged batteries to minimize the chances of thermal runaway and fire. However, studies have shown that material models calibrated at discharged state may not be as accurate at higher states of charge. In this study, a combined experimental-numerical method is proposed to simulate the stiffening of mechanical response in electrode stacks/jellyrolls of lithium-ion batteries at various states of charge and levels of confinement. Our study indicates that the mechanical properties of the jellyroll do not inherently change as a function of the state of charge, rather, the primary cause of the higher stiffness in charged batteries is the volume expansion of the jellyroll during charging. Therefore, mechanical characterization tests are conducted at the discharged state and the expansion of the jellyroll is induced in the finite element models to match the equivalent volume at the desired state of charge. In the second phase of the simulation, mechanical abuse loading is applied to validate the accuracy of simulations using the test data. This method was applied and validated for both pouch and cylindrical batteries with high accuracy.

Study on the formation and characteristics of unstable sheet cavitation on hydrofoils

Hydrofoils, as fundamental components of hydraulic machinery, directly influence the performance of such machinery. This study conducted an analysis of the cavitation characteristics of hydrofoils at a + 4° angle of attack under various cavitation numbers using numerical simulation and experimental research methods. The focus of the research was to explore the phenomenon of unstable sheet cavitation and its causes, as well as to reveal the characteristics of the re-entrant jet. The large eddy simulation method was employed to calculate the cavitation morphology under three different cavitation numbers. The method is highly consistent with the experimental results in simulating the small-scale detachment at the tail of unstable sheet cavitation and the large-scale shedding of cloud cavitation. The study found that the detachment of unstable sheet cavitation is closely related to the re-entrant jet, which exhibits transient and abrupt characteristics during the unstable sheet cavitation phase. Furthermore, by applying FFT processing to the distribution of maximum reverse velocity and the spatiotemporal changes of Ux on characteristic lines, eigenfrequency of the detachment of unstable sheet cavitation were identified. The research results indicate that cavitation mainly show as sheet cavitation when the cavitation closure point does not exceed the zero-slope point. Beyond this point, it transitions to cloud cavitation. This study provides new insights into the cavitation phenomenon of hydrofoils and offers quantitative research on the phenomenon of unstable sheet cavitation.

Study on the Diffusion Characteristics of Polymer Grouting Materials Applied for Crack Filling in Underground Mines Based on Numerical Simulation and Experimental Methods.

Polymer grouting materials are increasingly used in the filling of mine fissures. Unlike conventional inorganic grouting materials, the self-expansion of polymers adds complexity to their diffusion process within the crack. The objective of this research was to examine how polymer grouting material spreads in cracks at ambient temperatures and pressure. The investigation involved conducting grouting tests and performing numerical fluid simulation calculations using the finite-volume method in the computational fluid dynamics software, ANSYS FLUENT 2022 R1. The fluid volume approach was employed to determine the boundary between fluid and air and to ascertain the variation patterns of density in the slurry and the fracture system. This study applied the principles of fluid mechanics to investigate the patterns of variation in the physical characteristics of polymer grouting materials, including their density, pressure, flow velocity, and movement distance, during the diffusion process. The results indicated that the density of the polymer grouting material decreased exponentially over time throughout the diffusion process. With the increase in the grouting's volume, the grout's pressure and the permeable distance of the grout increased. The slurry's pressure near the grouting hole exceeded the other points' pressure. The physical parameters of the slurry were numerically simulated by ANSYS FLUENT 2022 R1 software, and the results were compared with the experimental data. After comparing the numerical simulation results with the test data, it was clear that the numerical simulation method was superior in accurately predicting the distribution pattern of each parameter of the polymer slurry during diffusion. The grouting volume, pressure distribution, and real-time change in the position of the flow of slurry could be efficiently determined through numerical calculation and simulated grouting tests. This work can offer valuable information for designing polymer grouting materials used in underground mine fissures.

Mechanical properties of a novel negative Poisson's ratio gradient structure

A novel cellular structure is proposed based on bionic structure with negative Poisson's ratio characteristic, and the cell is periodically expanded in the in-plane direction to create a new honeycomb structure. The influence of gradient changes of the structural parameters on the load-bearing capacity and damping characteristics of the structure is investigated through a combination method of finite element numerical simulations and experiments. The results indicate that the concentric gradient arrangement of cell wall thickness and angle parameters, and the symmetrical gradient arrangement of cell height, wall thickness and angle parameters have the most significant influence on the static bearing capacity of the structure. In contrast, the gradient arrangement under the corner circle diameter has minimal effect on the static bearing capacity of the structure. Under the same conditions, the peak values of the transmissibility of C2 (large angle at constraint end and loading end, and smaller angle in the middle) and C3 structures (angle gradually increases from the loading end to the constraint end) are significantly reduced between the frequency 2 Hz and 1024 Hz. The peak values of the transmissibility of the structures C2 and C3 are respectively decreased by 20% and 25% compared to that of the non-gradient structure. This shows that the vibration damping effect of these two structures is better. The structure with the gradient change and the structure without the gradient change of the new honeycomb structure can both achieve certain vibration reduction and isolation from the middle to high frequency range.

Application of deep learning for technological parameter optimization of laser shock peening of Ti-6Al-4V alloy

The paper is devoted to the development of the method of laser shock peening (LSP) of metals. To optimize the mode of LSP for Ti-6Al-4V specimens a deep learning model for predicting residual stresses by laser shock peening was developed. A numerical-experimental method was used to carry out the model training, in which an experimental study of the effect of different processing mode on the depth and distribution of residual stresses was carried out. The Johnson-Cook model was used as the governing relationship for modeling the dynamic deformation process. At the second stage, the problem of static equilibrium of a body with a plastically deformed area was numerically solved to determine residual stresses. The results of research on determination of the optimal configuration of the deep learning model showed that when using sinusoidal activation function of the neural network with 4 hidden layers and the number of neurons 10, the best level of accuracy in solving the problem is achieved. The obtained model allows us to optimally determine the LSP mode according to the given limitations of values and depth of residual stresses.

Analysis of cooling effects and measurement errors in water-cooled thermocouples for total temperature measurement in aviation engine combustion chambers

Accurate measurement of the total temperature in the main combustion chamber of an aviation engine is crucial for assessing engine performance. However, a significant challenge exists in balancing the heat transfer errors caused by the necessary cooling of the measuring device with measurement precision. The research employs a combination of numerical simulations and experimental methods to investigate this issue. The numerical simulations utilized the Reynolds-averaged Navier Stokes (RANS) coupled with a conjugate heat transfer approach to study the primary flow characteristics and heat transfer properties within the combustion chamber and the probe body. The experiments were conducted in a heat-calibration wind tunnel, validating the results of the numerical simulations. The results show that by implementing water cooling, the probe's body temperature can be reduced from 1200 °C in high-temperature conditions to 400 °C, with localized temperature imbalances still present in the edge areas of the probe. Tracing the cooling water path reveals that the vertical bends in the internal channels lead to an increase in localized pressure loss of the cooling water. The study quantitatively analyzes measurement errors caused by three heat transfer modes: radiation, convection, and conduction. In low-load conditions of the combustion chamber, heat conduction plays a dominant role, with measurement errors due to conduction reaching up to 70 % of the total measurement error. Radiation further increases the temperature measurement errors of the thermocouple's junctions near the chamber wall. As the combustion chamber temperature increases, entering high-load conditions, the cooling effect of water becomes limited, reducing conduction errors and increasing radiation errors. In these conditions, radiation errors constitute 60–70 % of the total measurement error. It suggests the importance of considering temperature corrections when using water-cooled temperature measurement devices. The research reveals several crucial insights regarding the performance and limitations of water-cooled thermocouples.

Deformation and failure behavior of 2024-T42 sheet under impact loading

The deformation and failure behavior of 2024-T42 aluminum alloy sheet was investigated through a combined experimental-numerical method. Nine types of specimens were designed to cover a wide range of stress triaxialities and strain rates. Quasi-static and dynamic tests were carried out by electronic testing machine and split Hopkinson tensile bar respectively, and digital image correlation (DIC) method was introduced to measure the deformation. The phenomenological damage model GISSMO (generalized incremental stress state dependent damage model) and Johnson-Cook model were adopted to simulate all of the above tests and the load-displacement curves through numerical simulation were derived. An optimization method was developed to obtain all the model parameters by matching the load-displacement curves from simulation with those from tests by LS-OPT. Finally, drop weight tests and tensile tests of the central-hole plate were conducted. The applicability and accuracy of the damage models were verified by comparing the simulation results with the experiments, which indicates that GISSMO model predicts better the tests than the Johnson-Cook failure model.

High-precision meshfree methods for solving 3D radiation diffusion problem in irregular spaces

Radiation diffusion is a significant phenomenon in inertial confinement fusion, geology and so on. Solving nonlinear radiation diffusion equation in irregular spaces is challenging. In this paper, the direct linearisation algorithm and the successive permutation iteration algorithm are constructed for solving 3D radiation diffusion equation, which are full-implicit discretization on time. The high-precision meshfree methods are provided by the Kansa's non-symmetric collocation method with the compactly supported radial basis function. Ultimately, the accuracy and efficiency of the presented algorithms are verified through the comparison of the fixed point, Newton and SOR methods in 3D numerical experiments. These novel meshfree methods not only avoid the complexity of grid generation, but also provide high-precision numerical solution for nonlinear radiation diffusion equation.

Effect of inlet water vapor mass fraction on flow characteristics in Laval nozzle

Abstract The Laval nozzle is an important component of the supersonic cyclone to achieve the change of gas–liquid two-phase, and the condensation characteristics of the Laval nozzle have an important influence on the separation performance of the supersonic cyclone. In this work, the effect of inlet water vapor mass fraction on the condensation characteristics in the Laval nozzle was investigated using numerical simulation and experimental methods by establishing a three-dimensional numerical model of air-water vapor supersonic condensation flow. The flow field structures in the Laval nozzle under different inlet water vapor mass fractions were investigated, including Mach number, pressure, and temperature and the effects of the inlet water vapor mass fraction on the liquefaction characteristics in the Laval nozzle were investigated. In addition, the droplet distribution in the Laval nozzle were also tested by a particle image velocimetry (PIV) experimental system. The comparison of simulation and experimental results indicates that the numerical model established in this work can effectively describe the real flow situation in the Laval nozzle. The results show that the inlet water vapor mass fraction has a little effect on the flow field structure in the Laval nozzle, and has the significant impact on the water vapor condensation characteristics. With increasing the inlet steam mass fraction from 5 % to 12.5 %, the nucleation rate, droplet number, and separation efficiency in the Laval nozzle increase to 4.05 × 1021 kg−1 s−1, 3.67 × 1014 kg−1, and 79.4 %, respectively, and when further increasing the inlet steam mass fraction to 15 %, these parameters decrease.

The mechanism of internal energy losses in double- suction centrifugal pumps under direct and reverse conditions

The double-suction centrifugal pump has gained extensive application in various hydraulic projects and industrial processes under direct and reverse operating conditions. However, the occurrence of unstable flow phenomena, such as flow separation, vortex and reflux, poses a significant challenge to its hydraulic performance. Therefore, this paper aims to analyze the energy loss and energy dissipation mechanisms in double-suction centrifugal pumps operating in both direct and reverse conditions. By utilizing the entropy production theory, a combination of numerical simulations and experimental methods are employed to investigate the energy loss of double-suction centrifugal pump compared to double-suction centrifugal pumps as turbines. The findings indicate that the turbulent entropy production loss and wall entropy production loss are the principal contributors, accounting for over 57 % and 33 % of the total entropy production loss, respectively, under different flow conditions of the pump and turbine. Conversely, the direct entropy production loss is not more than 1 %. This suggests that the main causes of energy losses are associated with wall effects in the near-wall region and unstable flow in the main flow region. Within the pump conditions, the main components responsible for energy loss are the volute and impeller. Conversely, under turbine conditions, the impeller and draft chamber are the main contributors to energy loss. The presence of a suction chamber rib proves beneficial under pump conditions as it diverts and optimizes internal flow. However, the draft chamber flow divider exacerbates energy losses under turbine conditions. This study not only provides insights into the energy loss characteristics of a double-suction pump operating under direct and reverse conditions but also offers a fresh perspective on the structural optimization of both the double-suction pump and double-suction pump as turbine.

Research study of passenger cars repair costs depending on the vehicle make, type of spare parts and the entity providing the service

The high number of road accidents has significant social importance, both in the context of households and enterprises, because each vehicle damage entails financial outlays related to the repair of damaged vehicles. This article analyses the most common types of vehicle damage occurring in road traffic. The object of the research were the vehicles most frequently purchased in Poland in 2022. The research process involved numerical experiment method using the AUDATEX system to determine costs enabling to repair such damage. The analyses take into account various repair options, such as: Authorized Service Station, independent workshop, and conditions proposed by insurance companies in Poland. The research showed cost dependencies between variables such as the vehicle brand, the type of spare parts and the entity providing the service.

Investigating crossflow interactions in multi-perforation cooling systems: Experimental and numerical insights

This study investigates the effects of employing a multi-perforation cooling system on crossflow interactions, utilizing both numerical simulations and experimental methods. A 30° inclined multi-perforation cooling system is applied on a heated flat plate as part of the experimental setup. Large Eddy Simulation (LES) is utilized for Computational Fluid Dynamics (CFD) calculations to analyze the impact of multi-perforation on heat transfer dynamics. Validation is conducted by comparing the results with experimental investigations. The study encompasses both aerodynamic and thermal considerations, employing Particle Image Velocimetry (PIV) and infrared techniques for analysis, while wall heat flux is measured using electrical discharge. Experimental data on film cooling are collected through these methods, focusing on the impact of blowing ratio (M) and the number of open jet rows (R). The LES-based CFD simulations accurately predict the trajectory of the cooling film. Notably, the influence of flow through the multi-perforation on the primary flow is observable across both configurations of open jet rows (4R and 8R near the wall). The outcomes substantiate the formation of a cooling film emanating from the jet’s fourth row (4R configuration), thereby validating the LES simulations. Visualization of wall temperatures illustrates the formation of a cooling film, discernible through the visible heat distribution from row 4R. However, discrepancies arise in predicting the adiabatic cooling efficiency towards the exit of the 4R region and the commencement of the 8R region, potentially attributed to the alterations induced by the additional multi-perforated injection. The novelty and the main objective of this study is to evaluate the impact of the variation of geometric parameters between the jets and the main flow on the dispersion of the jets themselves. A novel function, tailored to the temperature evolution of the cooling gas, is employed for data analysis. Two geometry configurations, featuring varying open hole areas, are evaluated. The film-cooled heat transfer coefficient, depicted by the Nusselt number, and the adiabatic film cooling efficiency results, serve to appraise the film cooling efficacy of the configurations.

Shuffled multi-channel sparse signal recovery

Mismatches between samples and their respective channel or target commonly arise in several real-world applications. For instance, whole-brain calcium imaging of freely moving organisms, multiple-target tracking or multi-person contactless vital sign monitoring may be severely affected by mismatched sample-channel assignments. To address this issue systematically, we frame it as a signal reconstruction problem where correspondences between samples and channels are lost. Assuming a sensing matrix for the signals, we show the problem’s equivalence to a highly structured unlabeled sensing problem and establish conditions for unique recovery. This is crucial since existing unlabeled sensing theory is inapplicable and results for reconstructing shuffled multi-channel signals do not yet exist. Our results extend to continuous-time sparse signals, and we derive conditions for reconstructing shuffled sparse signals. For the two-channel case, we provide a first reconstruction method, which combines sparse signal recovery with robust linear regression, outperforming existing unlabeled sensing methods in numerical experiments. Additionally, we showcase its effectiveness in a real-world application involving calcium imaging traces. Our theory marks a significant initial step in addressing this challenging signal reconstruction problem, with potential extensions to diverse signal representations encountered in real-world problems with imprecise measurement or channel assignment.

Optimization of tunnel grouting detection technology based on ultrasonic phased array

Due to the lack of a perfect and convenient method to detect the grouting quality of shield tunnels, an optimized ultrasonic phased array tunnel grouting detection technology is proposed. The particle swarm genetic algorithm is optimized to be used for phased array sparse, and the GA-VMD-SG algorithm is proposed to be used for noise reduction of ultrasonic detection signals, and numerical simulation and experimental methods are used to validate the optimized detection effect of the ultrasonic phased array. The results show that: the GA-PSO algorithm can better simplify the array and reduce the maximum sidelobe value; the GA-VMD-SG algorithm can well reduce the noise of ultrasonic signals; numerical simulation and experiments verify the feasibility of the ultrasonic phased array to detect the quality of grouting and the optimization effect of the two algorithms.