Full Three-dimensional Simulations Research Articles

Multidisciplinary Optimization of Gyroid Topologies for a Cold Plate Heat Exchanger Design

Abstract The strive to reduce the environmental impact of aviation has led to electrification and increasing demand for powerful on-board power electronic systems. These high-performance electrical components are bound to produce significant amounts of low-quality heat waste that, if not dissipated properly, will lead to malfunctioning and even permanent damage. For this reason, high-performance heat exchangers (HX) represent a key enabler for future advances in aircraft systems electrification and are vital to meet net zero goals and reduce the aviation's carbon footprint. For a given volume of the exchanger, the heat flow rate can be increased by adopting more sophisticated fluid domains. However, excessive geometrical complexity will lead to an increase in pressure losses, often resulting in inhomogeneous temperature distributions. In this paper, a novel optimization procedure is employed to maximize the efficiency of a high-performance heat exchanger, while minimizing overall pressure loss and temperature gradients. The optimization is performed with full three-dimensional high-fidelity computational flow simulations. The geometry of the fluid domain is constituted by triply periodic minimal surfaces (TPMS), with a parametrization based on thickness and aspect ratios, done by using the ntopology suite. To assess the performance gain, the topology-optimized design is compared against the datum case and a conventional serpentine design.

Computation of acoustic scattered fields and derived radiation force and torque for axisymmetric objects at arbitrary orientations.

This study presents a theoretical framework for calculating acoustic scattering fields, as well as radiation force and torque resulting from the interaction between an incident wave and an axisymmetric object positioned at arbitrary orientations. Grounded in the partial-wave expansion method, it formulates scattering products using beam-shape and scalar scattering coefficients. The incorporation of geometric features into the scalar scattering coefficients is achieved through the conformal transformation approach. Notably, its applicability is restricted to scenarios where the object is positioned at its standard orientation, a limitation circumvented by employing rotational transformations to extend the model to non-standard orientations. A rotational transformation tunes the original frame (observation coordinate system) into a reference frame (computation coordinate system), for any deviated orientation and facilitating solution of scattering products. While the non-intuitive nature of rotational transformations disrupts the inheritability of the partial-wave expressions for the scattering products, an alternative approach is provided based on rotation addition theorem. This method directly incorporates object orientations into the beam-shape and scalar scattering coefficients, bypassing rotational transformations and preserving the partial-wave format. Comparative analysis with full three-dimensional numerical simulations shows theoretical methods are computationally more efficient while ensuring substantial consistency.

Dynamics of turbulent natural convection in a cubic cavity with centrally placed partially heated inner obstacle

Natural convection in a cavity with a partially heated obstacle at the center at the Rayleigh number Ra=1.46×109 is investigated using large eddy simulation (LES). The standard and dynamic Smagorinsky models, as well as the wall-adapting local eddy-viscosity model, are used for the subgrid scales, and the flow statistics are compared with recent experiments. The LES results obtained with different meshes show overall good agreement with the experiments as concerns the flow and heat transfer. Simulation with a non-ideal wall at the adiabatic side of the obstacle is also performed to explain the residual discrepancies observed in the unheated channel. Additional simulations performed with periodic conditions in the spanwise direction are very different from the full three-dimensional (3D) simulations, which demonstrate the significance of 3D effects in the cavity. In particular, periodic simulations show Tollmien–Schlichting kind waves in the transitional region, while the 3D cavity shows an early cross-flow transition to turbulence.

Stability analysis of heavy machinery moving on weak subsoil. 3D FEM model vs. analytical models

In this paper, the authors present an extension of the scope of the previously conducted research to the full three-dimensional computer simulation (using the finite element method), which takes into account the interaction between: heavy caterpillar tracks system – working platform – weak subsoil. The article presents a computer model considering two caterpillars, resting on elastic-plastic sub-soil, with standard Mohr-Coulomb yield conditions, allowing for computer simulation of the behavior of the system up to achievement of ultimate limit state. The results of the above model are treated as the reference for a simplified Analytical Models of estimating the limit state, which might be used in design procedures. In turn, these Analytical Models are enhancements of previously presented one. The most important results concluding form the Analytical Model are simple interaction formulas, in the space of moments acting on the machine-subsoil system, limiting a domain of safety in given soil conditions.

Jetting bubbles observed by x-ray holography at a free-electron laser: internal structure and the effect of non-axisymmetric boundary conditions

In this work, we study the jetting dynamics of individual cavitation bubbles using x-ray holographic imaging and high-speed optical shadowgraphy. The bubbles are induced by a focused infrared laser pulse in water near the surface of a flat, circular glass plate, and later probed with ultrashort x-ray pulses produced by an x-ray free-electron laser (XFEL). The holographic imaging can reveal essential information of the bubble interior that would otherwise not be accessible in the optical regime due to obscuration or diffraction. The influence of asymmetric boundary conditions on the jet’s characteristics is analysed for cases where the axial symmetry is perturbed and curved liquid filaments can form inside the cavity. The x-ray images demonstrate that when oblique jets impact the rigid boundary, they produce a non-axisymmetric splash which grows from a moving stagnation point. Additionally, the images reveal the formation of complex gas/liquid structures inside the jetting bubbles that are invisible to standard optical microscopy. The experimental results are analysed with the assistance of full three-dimensional numerical simulations of the Navier–Stokes equations in their compressible formulation, which allow a deeper understanding of the distinctive features observed in the x-ray holographic images. In particular, the effects of varying the dimensionless stand-off distances measured from the initial bubble location to the surface of the solid plate and also to its nearest edge are addressed using both experiments and simulations. A relation between the jet tilting angle and the dimensionless bubble position asymmetry is derived. The present study provides new insights into bubble jetting and demonstrates the potential of x-ray holography for future investigations in this field.

Intense mid-infrared laser pulse generated via flying-mirror red-shifting in near-critical-density plasmas

Abstract Relativistic femtosecond mid-infrared pulses can be generated efficiently by laser interaction with near-critical-density plasmas. It is found theoretically and numerically that the radiation pressure of a circularly polarized laser pulse first compresses the plasma electrons to form a dense flying mirror with a relativistic high speed. The pulse reflected by the mirror is red-shifted to the mid-infrared range. Full three-dimensional simulations demonstrate that the central wavelength of the mid-infrared pulse is tunable from 3 $\rm{\mu m}$ to 14 $\rm{\mu m}$ and the laser energy conversion efficiency can reach as high as 13%. With a 0.5-10 PW incident laser pulse, the generated mid-infrared pulse reaches a peak power of 10-180 TW, which could be interesting for various applications in ultrafast and high-field sciences.

Effects of excess oxidizer coefficient on RBCC engine performance in ejector mode: A theoretical investigation

This study investigates the effects of the primary rocket’s excess oxidizer coefficient (EOC) on the performance of a kerosene-fueled rocket-based combined cycle (RBCC) engine operating in ejector mode using the diffuser and afterburning (DAB) cycle. Employing complete mixing and chemical equilibrium assumptions, a quasi-one-dimensional model is developed to simulate combustion processes in the primary rocket chamber, mixer, and afterburner. Experimental data and full three-dimensional simulation validate the model’s accuracy. Results indicate that increasing EOC mitigates thermal choking effects at the mixer exit, decreasing mixing and Rayleigh losses, enhancing the entrainment ratio, and providing more oxygen for secondary combustion. However, the gas mixture’s compression ratio and total temperature decrease, rendering secondary combustion more susceptible to thermal choking in a constant cross-sectional afterburner. As the flight Mach number increases from 0.8 to 2.5, the optimum EOC for maximum specific impulse shifts from 0.725 to 2.375. While the optimum EOC for maximum thrust remains consistently around 2.0. The findings underscore the necessity of a higher EOC to fully unlock the DAB cycle’s thrust augmentation potential.

Experimental and simulation study of an automobile cooling system: Performance improvement using passive flow control

The performance of an automobile cooling system has substantial impacts on the engine's efficiency, fuel consumption, and CO2 emission. In this novel experimental and numerical investigation, a combination of full three-dimensional car simulation, and one-dimensional modeling of the radiator along with the results of road tests on two car models, namely Vehicle A (the base car) and Vehicle B, was used to evaluate and compare the performance of the vehicles' cooling systems. The effects of implementing a passive flow control as well as changing the angle and geometry of the air deflectors on the cars' performance were investigated. The simulation utilized the K-epsilon (k-ε) turbulence model, while the experimental section involved standard road cooling tests. The results show that modifying the air deflectors in Vehicle B enables quick cooling of the system by controlling the air flow rate moving toward the radiator, which increased the air mass flow rate through the condenser and the radiator by 13% and 21%, respectively. Also, the radiator inlet water temperature decreased by about 1.9 °C, and the fuel consumption was reduced by approximately 0.5% under the New European Driving Cycle (NEDC) conditions, which decreased the greenhouse gas emissions, namely CO2 by about 0.9%.

Full three-dimensional computational fluid dynamics simulation and optimization of a swirling jet-induced cavitation reactor

Hydrodynamic cavitation is an efficient method in terms of energy consumption that can be used to intensify the pollutant degradation processes in wastewater treatment. Among various kinds of cavitation reactors, a swirling jet-induced cavitation reactor that has been less studied was investigated in detail for the first time in this work. Recently, researchers have focused more on investigating the parameters that affect the process and control its intensity. In the present work, the efficacy of the operating pressure on the performance of the cavitating device was investigated by calculating the cavitational efficacy ratio (CER) using full three-dimensional computational fluid dynamics simulations. Also, preliminary studies were carried out for the first time to optimize the curvature correction coefficient of the shear stress transport k–ω viscous model to sensitize it to streamline curvature to obtain convergence and stability of the simulations. The optimum operating pressure was found by solving the cavity dynamics equations and calculating the CER parameter. The Rayleigh–Plesset cavity dynamics equation was applied to the cavity trajectory obtained from solving the discrete phase model to track the cavity radius and inside pressure variations. Finally, the validation of the simulation and estimated optimum operating pressure were done by the experimental data reported in the literature that there was reasonable agreement between them.

Electromagnetically driven anticyclonic rotation in spherical Couette flow

The electromagnetically driven anticyclonic flow in the wide gap of a rotating concentric spheres system is studied experimentally and numerically in the laminar regime. The working fluid is an electrolyte contained in the spherical gap. The outer sphere rotates at constant angular speed, and the inner sphere is at rest. The electromagnetic stirring is generated due to the interaction of a direct current, which is injected radially through ring-shaped electrodes located at the equatorial zone of each sphere, and a dipolar magnetic field produced by a permanent magnet located inside the inner sphere. Experimental velocity fields in the equatorial plane were obtained with particle image velocimetry. Additionally, full three-dimensional numerical simulations were performed. The high shearing at the equatorial region promotes an instability that can be perceived as a triggering mechanism of four tornado-like vortical structures tilted and entangled in the polar direction. The instability structure rotates in either the cyclonic or the anticyclonic direction, depending on the flow parameters, namely, the angular velocity of the outer sphere and the applied electric current. To the best knowledge of the authors, this is the first time the phenomenon under study is reported with electromagnetic forcing. The numerical results agree quantitatively with the experimental observations.

Chemical Imaging of Mass Transport Near the No-Slip Interface of a Microfluidic Device using Attenuated Total Reflection–Fourier Transform Infrared Spectroscopy

Mass transport in geometrically confined environments is fundamental to microfluidic applications. Measuring the distribution of chemical species on flow requires the use of spatially resolved analytical tools compatible with microfluidic materials and designs. Here, the implementation of an attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) imaging (macro-ATR) approach for chemical mapping of species in microfluidic devices is described. The imaging method is configurable between a large field of view, single-frame imaging, and the use of image stitching to build composite chemical maps. Macro-ATR is used to quantify transverse diffusion in the laminar streams of coflowing fluids in dedicated microfluidic test devices. It is demonstrated that the ATR evanescent wave, which primarily probes the fluid within ∼500 nm of the channel surface, provides accurate quantification of the spatial distribution of species in the entire microfluidic device cross section. This is the case when flow and channel conditions promote vertical concentration contours in the channel as verified by three-dimensional numeric simulations of mass transport. Furthermore, the validity of treating the mass transport problem in a simplified and faster approach using reduced dimensionality numeric simulations is described. Simplified one-dimensional simulations, for the specific parameters used herein, overestimate diffusion coefficients by a factor of approximately 2, whereas full three-dimensional simulations accurately agree with experimental results.

Interstellar Probe — Where is the “Nose” of the Heliosphere?

ABSTRACT In this paper are reviewed publications that were concerned about the discovery of the location of the heliopause “nose” by the Newtonian Approximation method and publications using the full three-dimensional magnetohydrodynamic simulations of the heliosphere that confirmed that discovery. Since we do not have a clear answer to the question of what the heliosphere looks like, in connection with the planned launch of the Interstellar Probe within this decade, there was a problem with deciding which direction to send it. The discovery of the movement of the “nose” of the heliopause depending on the direction of the interstellar magnetic field and the determination of the position of the “nose” is very important for this decision. Therefore, the purpose of the article is to answer the question of where is the “nose” of the heliopause. In the second part of the article, the possibility of changing the paradigm of scientific research projects related to interstellar missions (including those focused on the study of the heliosphere), among other things, by increasing the interdisciplinarity of research, is explored. As part of initiating such cooperation, the article develops social sciences themes related to the sustainable logistics of Interstellar Probe missions to increase public involvement in these projects.

Airflow Mitigation and Pollutant Purification in an Idealized Urban Street Canyon with Wind Driven Natural Ventilation: Cooperating and Opposing Effects of Roadside Tree Plantings and Non-uniform Building Heights

A refined CFD research was reported, concerning on the individual characteristics of different roadside tree planting and street canyon with non-uniformity of buildings. In this work, airflow field and pollutant dispersion were simulated by the use of a full three-dimensional simulations. Ventilation air exchange rate (ACH) and net escape velocity (NEV) were, respectively applied to assess ventilation exchange and pollutant dispersion in the street canyons. Numerical results show that the airflow patterns within the street canyon varies significantly with canopy leaf area density (LAD) and trunk height (Htb), whereas the distribution of pollutants at pedestrian level in the street canyon is mainly determined by the symmetrical inverse vortex structure of the street canyon. Promotions of LAD and Htb of the road trees simultaneously reduce the wind velocity, ACH and NEV of the street canyon, deteriorating the ventilation exchange conditions as well as the pollutant dispersion performance. As the value of the Htb becomes larger, NEV of the step-up canyon is approximately approaching to that of the step-down canyon. In addition, as the value of standard deviation (σH) of the street canyon increases, the vortex structure of the canyon disappears and promotes the diffusion of pollutants inside canyons. As σH further increases, ACH of the step-down canyon also boosts, indicating better ventilation performance of street canyon, whereas the step-up canyon only tops the best ventilation performance at the value of σH= 33.3%. The best dispersion of pollutants is observed at σH= 16.7% in the step-down canyon while in the step-up canyon the dispersion of pollutants becomes better continuously with increasing σH. In particular, as σH= 66.7% was maintained, the dispersion of pollutants is better in the step-up canyon compared to the street canyon without trees. At the same time, the difference between the NEV of the step-down canyon and the step-up canyon increases as σH increases, which indicates that the difference in pollutant dispersion performance between adjacent street canyons becomes greater. This research provides a theoretical reference for urban design and vegetation planning in urban areas to improve the habitat.

Stable, entropy-pressure compatible subsonic Riemann boundary condition for embedded DG compressible flow simulations

One approach to reducing the computational cost of simulating transitional compressible boundary layer flow is to adopt a near body reduced domain with boundary conditions enforced to be compatible with a computationally cheaper three-dimensional RANS simulation. In such an approach it is desirable to enforce a consistent pressure distribution which is not typically the case when using the standard Riemann inflow boundary conditions. We therefore revisit the Riemann problem adopted in many DG based high fidelity formulations.Through analysis of the one-dimensional linearized Euler equations it is demonstrated that maintaining entropy compatibility with the RANS simulation is important for a stable solution. It is also necessary to maintain the invariant for the Riemann outflow boundary condition in a subsonic flow leaving one condition that can be imposed at the inflow boundary. Therefore the entropy-pressure enforcement is the only stable boundary condition to enforce a known pressure distribution. We further demonstrate that all the entropy compatible inflow Riemann boundary conditions are stable providing the invariant compatible Riemann outflow boundary condition is also respected.Although the entropy-pressure compatible Riemann inflow boundary condition is stable from the one-dimensional analysis, two-dimensional tests highlight divergence in the inviscid problem and neutrally stable wiggles in the velocity fields in viscous simulations around the stagnation point. A two-dimensional analysis about a non-uniform baseflow assumption provides insight into this stability issue (ill-posedness) and motivates the use of a mix of inflow boundary conditions in this region of the flow.As a validation we apply the proposed boundary conditions to a reduced domain of a wing section normal to the leading-edge of the CRM-NLF model taken out of a full three-dimensional RANS simulation at Mach 0.86 and a Reynolds number of 8.5 million. The results show that the entropy-pressure compatible Riemann inflow boundary condition leads to a good agreement in pressure distribution.

Experimental and numerical investigation of bistability in rotating permanent magnet-generated electrolyte flow in a ring-shaped container

Here, the stability of a transversely magnetized rotating permanent magnet-generated flow in a concentric cylindrical ring channel is studied. Numerical calculations show that the steady-state solution becomes asymmetric through a pitchfork bifurcation at a Reynolds number (Re) of 60. The two new antisymmetric steady-state solutions become cyclic at Re = 90. Nonlinearities develop at larger Re values and the limit cycle solutions are destabilized at Re = 250, enabling random transition events between the two pitchfork branches. Such transitions have been observed in all kinds of natural phenomena, spanning from neuroscientific to astrophysical systems, which are often too complex to be directly computed. Our presented system is physical yet simple enough to be used to conduct a parametric study with full three-dimensional direct numerical simulations. It raises the possibility of numerically and experimentally analyzing transitions in more detail. Experimental measurements indicated the existence of long-lived states and suitability for the proposed system for future studies of such phenomenon. However, the experimental results did not conclusively observe bistability.

Computational Modeling of Microwave Tumor Ablation.

Microwave ablation is recognized as a minimally invasive, fast-recovery treatment for destroying cancer cells using the heat generated by microwave energy. Despite the unquestionable benefits of microwave ablation, the interaction of the microwave applicator with the tissue may result in localized heating and damage to the surrounding tissue. The majority of the tissue damage can be removed by clarifying the conditions for their development. In addition to experimental methods, computer modeling has proven to be an effective tool for optimizing the performance of microwave ablation. Furthermore, because the thermal spread in biological tissue is difficult to measure, developing a predictive model from procedural planning to execution may have a substantial influence on patient care. The comprehension of heat transport in biological tissues plays a significant role in gaining insight into the mechanisms underlying microwave ablation. Numerical methods that enable ablation size control are required to guarantee tumor destruction and minimize damage to healthy tissues. Various values of input power and ablation time correspond to different tumor shapes ensuring the preservation of healthy tissues. The optimal conditions can be estimated by performing full three-dimensional simulations. This topical review recapitulates numerous computational studies on microwave tumor ablation. Novel areas emerging in treatment planning that exploit the advantages of numerical methods are also discussed. As an illustration, the results of the three-dimensional simulations of real liver tumors in the 3D-IRCADb-01 database are presented and analyzed. The simulation results confirm that numerical methods are very useful tools for modeling microwave tumor ablation with minimal invasiveness and collateral damage.

Wind turbine wake simulation with explicit algebraic Reynolds stress modeling

Abstract. Reynolds-averaged Navier–Stokes (RANS) simulations of wind turbine wakes are usually conducted with two-equation turbulence models based on the Boussinesq hypothesis; these are simple and robust but lack the capability of predicting various turbulence phenomena. Using the explicit algebraic Reynolds stress model (EARSM) of Wallin and Johansson (2000) can alleviate some of these deficiencies while still being numerically robust and only slightly more computationally expensive than the traditional two-equation models. The model implementation is verified with the homogeneous shear flow, half-channel flow, and square duct flow cases, and subsequently full three-dimensional wake simulations are run and analyzed. The results are compared with reference large-eddy simulation (LES) data, which show that the EARSM especially improves the prediction of turbulence anisotropy and turbulence intensity but that it also predicts less Gaussian wake profile shapes.

Effect and Mechanism of Roughness on the Performance of a Five-Stage Axial Flow Compressor

In order to prolong the service life of multistage axial compressors, it is increasingly important to study the influence of blade surface roughness on the compressor performance. In this paper, a five-stage axial compressor of a real aero-engine was selected as the research object, and an equivalent gravel roughness model was used to model the roughness based on measured blade surface roughness data. Furthermore, the impact of blade surface roughness on the performance at design rotational speed was studied by full three-dimensional numerical simulation, and the mechanism of performance variation caused by the roughness was discussed combined with quantitative and flow field analyses. The results show that, when the blade surface roughness of all blades increases, the peak total efficiency decreases by approximately 0.4%, the blocking mass-flow decreases by approximately 0.3%, and the stable working range changes little. When the surface roughness of all rotor blades increases, the performance decline is close to that of all rotor and stator blades, and the variation in stator blade roughness has little effect on the compressor performance. Regarding the variation in roughness, the performance of the latter stage is more sensitive than that of the previous stage, and the decline in the performance of the fifth stage contributes the most to the total performance degradation of the compressor. Once the surface roughness of the fifth-stage rotor blade increases, the flow in the middle of the rotor blade deteriorates and the stage performance decreases obviously, which is the main reason for the decline in the overall performance.

Experimental and Numerical Investigation of Rotor–Stator Interaction in a Large Prototype Pump–Turbine in Turbine Mode

In recent years, large-capacity, high-head pump–turbine units have been developed for pumped storage power plants to effectively utilise water energy and store large amounts of electricity. Compared with the traditional Francis turbine unit, the radial distance between the trailing edge of the guide vanes and the leading edge of runner blades of high-head pump–turbine unit is smaller, so the rotor–stator interaction and the corresponding pressure fluctuations in the vaneless space of pumped storage units are more intense. The pressure fluctuations with high amplitudes and high frequencies induced by rotor–stator interaction (RSI) become the main hydraulic excitation source for the structures of the unit and may cause violent vibration and fatigue damage to structural components, and seriously affect the safe operation of the units. In this paper, the RSI of a high-head pump–turbine in turbine mode of operation is studied in detail by means of site measurement and full three-dimensional unsteady simulations. The results of RSI-induced pressure fluctuations in turbine mode are analysed experimentally and numerically. The accuracy of the numerical calculations is verified by comparing with the measured results, and the variation law of RSI is deeply analysed. The results show that the pressure fluctuations in the vaneless space are affected by the wake of the guide vane, the rotating excitation of the runner, the low-frequency excitation of the draft tube, and the asymmetric characteristics of the incoming flow of the spiral case, and shows significant differences in spatial position. The findings of the investigation are an important and valuable reference for the design and safe operation of the pumped storage power station. It is recommended to design the runner with inclined inlets to reduce the amplitudes of RSI-induced pressure fluctuations and to avoid operating the pump–turbine units under partial load for long periods of time to reduce the risk of pressure fluctuation induced severe vibration on the structures.

Comparing two- and three-dimensional models of scrape-off layer turbulent transport

There exists a large body of previous work using reduced two-dimensional models of the scrape-off layer (SOL), which model fluctuations in the drift-plane but approximate parallel transport with effective loss terms. Full size three-dimensional simulations of SOL turbulence in experimental geometries are now possible, but are far more computationally expensive than 2D models. We therefore use a flux-tube geometry model of the SOL to compare the results of 2D simulations to 3D simulations with a similar setup, looking for systematic differences. Our setup mimics the outer SOL of a double-null plasma, with no neutrals and no shear, and is therefore likely more favourable to agreement. Overall, we do find good agreement in the basic radial profiles, probability distribution functions, and power spectra of fluctuations. However, the average temperature is over-predicted in 2D relative to 3D, and we explain the difference in terms of the effect of geometrical simplifications of devices at low power. Varying geometric parameters, we find that supersonic flow in the divertor leg, which occurs because our simulations do not include neutrals and so represent low-recycling conditions, means that the divertor leg length only has a weak effect on the output. Finally, we examine the effect of altering the magnitude of source and sink terms in 2D, concluding that they cannot easily be used to recreate both the density and temperature profiles observed in 3D simultaneously.