Flow Phenomena Research Articles

Numerical investigation of hydrogen ignition induced by unsteady flow phenomena

The purpose of the present study is to evaluate the possibility of using a gas dynamic heater as an igniter of the combustible gas mixtures. The impacts of some operating and geometrical parameters on average temperature of the gas dynamic heater are investigated by numerical simulation of axisymmetric turbulent flow in the resonance tube. The operating gas of the heater is air which is completely decoupled from the ignition chamber. The combustible mixtures under consideration is stoichiometric hydrogen-oxygen at atmospheric pressure, in which the ignition is studied solving the governing equations for one dimensional reacting flow using detailed chemistry. The finite volume method is used in the presently developed flow solver for numerical simulations. The results show that despite highly fluctuating temperature of the end wall of the resonance tube as a hot surface, it can provide proper condition for gas mixture ignition in the chamber, by adjusting an inlet pressure and geometry of the gas dynamic heater. The end wall average temperature depends on the nozzle inlet pressure and convergence angle of the resonance tube, and the results demonstrate that the characteristics of temperature time history of repeating cycles are so effective on ignition process.

A statistical boundary for 3D rarefied flows through meshes: implementation to a new version of dsmcFoam+ and wind tunnel validation

AbstractThe Direct Simulation Monte Carlo (DSMC) method has become a standard tool for rarefied aerodynamics and microchannel flows. However, the performance benefits of DSMC, such as adaptive grid sizes and number of particles, are constrained by the need to resolve small geometric details of mesh applications within relatively large simulation volumes. The requirement for a sufficient number of particles in even the smallest cells imposes a significant computational burden. A novel set of cyclic statistical boundary conditions is proposed to address the computational bottleneck associated with simulating micrometre-scale structures prevalent in atmospheric and space research under rarefied flow conditions. These conditions account for the geometric parameters of a geometric mesh and the angular dependency of impacting particles, aiming to alleviate the computational challenges posed by conventional approaches. Validation against wind tunnel measurements demonstrates excellent agreement for one of the implemented boundaries, able to simulate fine meshes for conditions of rocket soundings in the Mesosphere. The newly developed boundary conditions are implemented within the advanced DSMC solver, dsmcFoam+ framework. For this study, the solver is ported from OpenFOAM® version 2.4.0 to the OpenFOAM® version v2306 to leverage recent code developments, particularly in dynamic meshes, load balancing, and barycentric particle tracking. This advancement enhances the capabilities of DSMC simulations, offering improved fidelity and accuracy in capturing rarefied flow phenomena.

A developed transition simulation model for turbulent plane jet impingement heat transfer

Jet impingement has been widely used due to its high heat transfer rate, but numerical simulation of this flow is highly challenging because of complex flow phenomena. In this paper, a turbulence model based on the physics of jet impingement is developed using the shear stress transport (SST) four-equation transition model and the SST with cross-diffusion correction (SSTCD) model. The proposed method is evaluated for plane jet impingement under various nozzle-plate spacings (2.6, 4 and 6) and different Reynolds numbers ranging from 10,200 to 20,000 in terms of heat transfer and flow fields. The results show that the developed model has the ability to capture the second peak of heat transfer and skin friction at low nozzle-plate spacing. Even at high nozzle-plate spacing, this approach also gives accurate trends for the above two features. However, without the cross-diffusion correction, the transition model provides too high energy and low velocity peaks. With the developed model in hand, the effects of pressure gradient on heat transfer and skin friction coefficient are further investigated. It is found that when the adverse pressure gradient becomes strong, the position of the secondary peak of skin friction occurs earlier than that of the secondary peak of heat transfer rate. Conversely, if the adverse pressure gradient disappears, the positions of these features coincide.

Mechanism and experimental investigation on the formation of micro‐triangle stepped jet in composite spinning solution

AbstractIn the field of nanotechnology, rotary jet spinning technology has garnered attention due to its unique advantages in fabricating composite nanofibers. The composite nanofibers prepared using this technology exhibit exceptional purity, uniformity, and consistency, thereby enhancing reliability and controllability in practical applications. During the process of rotary jet spinning, the spinning solution flows into the nozzle and converges at a micro‐triangle under the combined influence of centrifugal force, viscous force, surface tension, and gravity. Stepped jet refers to the flow phenomenon occurring within a channel with a gradually decreasing cross‐sectional area. In this process, an increase in the flow velocity of the composite spinning solution aids in stabilizing stretching at the micro‐triangle which is crucial for forming continuous jets. This article analyzes cone formation mechanisms for composite spinning solutions and stepped jet principles while establishing corresponding models that reflect relationships between solution velocity magnitude and parameters such as rotational speed, concentration, and nozzle diameter. Finally, polyethylene oxide (PEO)/polyvinylpyrrolidone (PVP) composite nanofibers were prepared using a rotary jet spinning device where experimental investigation focused on examining how parameters such as rotational speed, solution concentration, and nozzle diameter impact motion of spinning solution within micro‐triangle.Highlights Preparation of PEO/PVP composite nanofibers by rotary jet spinning. Presentation of cone formation mechanisms for composite solutions. The stepped injection principle was proposed. Modeling of composite solution motion. Rotational speed, solution concentration, and nozzle diameter impact motion.

Numerical solution of an unsteady nanofluid flow with magnetic, endothermic reaction, viscous dissipation, and solid volume fraction effects on the exponentially moving vertical plate

This study analyzes the unsteady nanofluid flow phenomenon adjacent to an accelerating vertical plate under the influence of magnetic fields, chemical reactions,viscous dissipation and solid volume fraction factors. The analysis motivates the understanding of the behavior of complex fluids to improve existing processes and develop new technologies. The finite difference technique, with the help of the boundary and initial conditions, was employed for the numerical result. The numerical solutions were graphically analyzed through MATLAB software. The results reveal intricate flow behaviors, including the influence of magnetic fields and solid volume fraction in reducing the velocity of the nanofluid. Interestingly, a magnetic field drops the temperature of the nanofluid, which can be observed in a particular case. The chemical reaction is found to absorb the heat, leading to a decline in the velocity and concentration due to temperature drop and solute destruction factors. The viscous dissipation raises the temperature of the nanofluid, but the heat sink affects the temperature oppositely. The Soret number essentially quantifies the phenomenon known as thermophoresis, where solutes concentrate more in cooler regions. This analysis provides valuable insights into the design and optimization of systems involving nanofluids subjected to external magnetic fields, with implications for various engineering applications such as thermal management systems and nanofluid-based heat exchangers.

Interaction between lateral jet and hypersonic rarefied flow

Reaction control systems (RCS) are commonly utilized in a variety of air vehicles, and they give rise to complex flow phenomena. For flows dominated by shock waves and expansion, such as lateral jets, a significant gradient is formed in the local region of the flow field, resulting in a high local Knudsen number, and the continuum hypothesis is no longer applicable, even if the freestream belongs to near-continuum flow. As a result, multi-scale simulation approaches should be used to capture the interactions between these multi-scale structures and appropriately determine aerodynamic forces. Our earlier work, which used the conserved discrete unified gas kinetic scheme (CDUGKS) for monatomic gas, studied the flow field features of lateral jets and aerodynamic forces on blunt bodies under various rarefied freestream conditions. In this research, the Rykov model is used to expand the CDUGKS suit for diatomic gas flow while taking into account the excitation of molecular rotational energy. The impact on the flow field and aerodynamic forces from four parameters, namely freestream Mach number, jet Mach number, jet pressure ratio, and nozzle position, is thoroughly investigated. The results show that even if the incoming Mach number is different, the flow field structure and aerodynamic properties don't change much when the jet momentum ratio stays the same. The solid wall stagnation point value and local peak also show some linear relationships. The jet pressure ratio mainly affects the expansion characteristics of the jet, such as the influence range on the solid wall. In addition, with an increase in the distance between the nozzle position and the torque reference point, higher control efficiency can be obtained. The study of these aspects will help us comprehend lateral jet flow and provide reference for the design of an air vehicle's RCS.

Two-phase flow characteristic and gas removal strategy of the paper-based microfluidic fuel cell

Paper-based microfluidic fuel cell powered by capillary force has the advantages of compactness, low cost, and high sensitivity, presenting broad application prospects in portable electronic devices. However, the gas-liquid mass transfer mechanism within the porous medium remains unclear, with a lack of two-phase flow theories adapted to the unique paper-based system. In this study, a two-dimensional two-phase numerical model of a Y-shaped paper-based microfluidic fuel cell is developed to reveal the two-phase flow characteristics under capillary action and explore gas removal strategies. The reliability of the model is validated by real experimental data. By coupling multiple physical fields, the study elucidates the working principle and gas-liquid flow phenomena within the cell. Then, the effects of contact angle, inlet fuel concentration, and paper type on output performance, gas distribution, parasitic effect, and fuel utilization are discussed. The results indicate that increasing the contact angle and using paper with a larger average pore size and porosity as the channel substrate are ideal for promoting gas discharge. The optimal gas removal rate reached 42.30 %, with a favorable power density of 33.92 mW/cm2. This study provides a theoretical basis for a deeper understanding of the two-phase mass transfer process in paper-based microfluidic fuel cell.

Experimental investigation on a microfluidic U-turn channel for heat transfer applications

In the present work, an experimental set-up designed to allow investigations of the carrier fluid local behaviours in terms of velocity and temperature fields is presented. The study is carried out on a U-turn microfluidic channel, to bear a complete view of the thermo-fluidic system. The experiments have been performed by Infrared Thermal Imaging, which allows deriving the thermal field on the microchannel external walls, and inferring the internal thermal profiles through specific transfer functions in laminar and transitional regimes. Maps of thermal transients allow deriving cooling performances, which are used to identify the local thermal efficiency of the microchannel and relate it to the global efficiency. Velocimetry measurements have been conducted with a Micro Particle Image Velocimetry (μPIV) setup at different flow rates. This analysis has been coupled with thermal results to obtain a description of the effects of local fluid flow phenomena in transitional turbulent regime on the global heat transfer efficiency of a U shaped microchannel. The interactions among thermal and flow fields are specifically related to secondary recirculating flows, close to the turns, where high cooling rates and high magnitude of local velocity fluctuations are measured.

Ferromagnetic effect on Casson nanofluid flow and transport phenomena across a bi-directional Riga sensor device: Darcy–Forchheimer model

Abstract Ferromagnetic hybrid nanofluids can be employed in electronics and microelectronics cooling applications to minimise the accumulation of heat and effectively eliminate excess heat. By increasing the heat transfer rate, these nanofluids serve to maintain suitable operating temperatures and avoid device overheating. This study examines the influence of convective heating on the fluid flow of a three-dimensional ferromagnetic Casson hybrid nanofluid (composed of Mn-ZnFe2O4/CoFe2O4 nanoparticles) over a radiative Riga sensor device. The investigation takes place within a permeable medium characterised by Darcy–Forchheimer dynamics. Additionally, the analysis incorporates the assessment of the interaction of viscous dissipation. To establish a standardised set of governing partial differential equations along with their associated boundary circumstances, suitable similarity transformations are implemented. Following this, the resultant transformed ordinary differential equations are efficiently solved using the bvp5c solver. The solution process employs the shooting technique facilitated by MATLAB software. The impact of these influencing factors was carefully observed and thoroughly analysed using graphical representations. Specifically, the effects of pertinent factors on shear stress and heat transfer rates are concisely depicted in tabular formats.

A generative adversarial network for enhancing over-expansion flow field perception of nozzles with large expansion ratio

Over-expansion flow and separation phenomena exist inside the nozzle during the startup and shutdown of the rocket engine, and the transition between the separation modes is prone to cause significant side loads and jeopardize the safety of the engine. Accurate, comprehensive and prompt nozzle flow field state perception is of great significance to the stable operation of the engine. Here, a generative adversarial network is proposed to reconstruct the internal Mach number and temperature fields for different nozzle pressure ratios and flow separation modes based on the discrete pressure at the nozzle wall. The proposed generative adversarial network employs Wasserstein distance and gradient penalty to improve the problems of gradient vanishing and pattern collapse during discriminator network training. The large expansion ratio nozzle selected was the VOLVO S1 nozzle and numerical simulations were carried out under different nozzle pressure ratio conditions to obtain data for the training of data-driven model. The results indicate that generative adversarial networks can accurately reconstruct restricted shock separation and free shock separation modes under different nozzle pressure ratios based on discrete pressure and temperature measurement points on the nozzle wall, with a relative error of less than 1.2%, and accurately identify important flow field characteristics such as Mach disk, supersonic jet flow, and multiple recirculation regions. The advantages of the generative model in recognizing the strong normal shock Mach disk are compared with those of the supervised learning model. This study lays the foundation for the subsequent study of nozzle side load and structural fatigue life based on three-dimensional flow field.

Computational study of magnetohydrodynamic mixed convective flow in a nanofluid-filled cavity with diagonally moving lid

This study examines the phenomenon of uniform magnetohydrodynamic mixed convective flow in a cavity filled with nanofluid. The research focuses on analyzing the mixed convection induced by a uniformly heated lid-driven cavity with diagonal motion. The fluid and heat transport equations are solved using the finite volume method. Numerical simulations are conducted for various parameters including Richardson number (Ri) ranging as 0.1, 1 & 10, Hartmann number (Ha) 0, 10, 25 & 50, angle of inclination (γ) 0°, 30°, 45°, 60° & 90°, and solid volume fraction from 0.0 to 0.05. The results are presented in terms of flow and thermal fields. It is observed that higher Hartmann numbers and inclination angles of the magnetic field lead to a suppression of convection, favoring a dominant conduction mode and reducing the overall heat transfer rate. Specifically, the study highlights a significant enhancement in the heat transfer rate in a nanofluid-filled cavity with a diagonally moving wall. The movement’s of diagonal wall has significant power consumption, the tool may be used in an industrial process that improves heat transfer, offers flexibility, and raises the quality of the finished product. Additionally, the correlations that were found are a useful tool for heat exchanger design.

Flow of nanofluid past a radially stretching disk in an absorbent medium in company of multiple slips, nonlinear radiative heat flux and Arrhenius activation energy

AbstractAn investigation is carried out to analyze the flow, heat and mass transport phenomena of nanofluids over a disk stretched radially in a porous medium. Besides nonlinear radiative heat flux and Arrhenius activation energy, multiple slips are considered in this model. This ensures the novelty of the present research. The main goal of the current investigation is to explore the mutual impacts of nonlinear radiative heat flux, various slip factors and Arrhenius activation energy on flow, heat and mass transfers. The highly nonlinear central equations which are partial differential equations (PDEs) are transformed into nonlinear ordinary ones (ODEs) by employing suitable similarity alterations and then for finding the approximate numerical solutions, shooting technique with 4th order “Runge–Kutta method” are applied. The impact of a variety of parameters on “skin friction coefficient,” “Nusselt number,” “Sherwood number,” velocity of the fluid, heat and mass transfers are computed and presented graphically. It is interesting to observe that fluid velocity diminishes with the growing porosity, suction and velocity slip parameters. Nanofluid's temperature reduces for enhanced values of thermal slip parameter but for rising thermal radiation parameter, temperature is boosted up. Also, nanoparticle concentration diminishes for increasing values of mass slip parameter.

Enhancing fuel-air mixing in COG-BOG non-premixed combustion: A CFD analysis with different turbulent models

The present study investigates non-premixed combustion using a mixture of coke oven gas (COG) and blast oven gas (BOG) as fuel, with the help of computational fluid dynamics (CFD). The mixing and conversion were compared by employing three turbulent models: standard k-ɛ, renormalization group (RNG), and Reynolds stress model (RSM). Variations in oxidizer inlet angles (0°, 5°, and 10°) were explored for improved fuel-air mixing. Analyzing these models and designs also allowed the understanding of the flow phenomena. Flame patterns and maximum temperature produced were examined with varying fuel-oxidizer velocity ratios. The finding shows the RSM model with a 10° oxidizer inlet angle was outperforming the others, predicting a 4 % higher outlet temperature. In the case of analyzing a suitable turbulent model for simulating the combustion of COG-BOG mixture, the study revealed, the RNG model records 35 % lower temperatures which means poor conversion due to poor mixing. The produced temperature was closely related to the fuel-oxidizer ratio and a range of this ratio helped to identify the optimized controlling parameter. This research advances knowledge of COG-BOG combustion simulation, aiding in the compatibility of turbulence models, oxidizer-fuel optimization, and improvements to phase flow.

Magnetohydrodynamic Darcy-Forchheimer flow of non-Newtonian second-grade hybrid nanofluid bounded by double-revolving disks with variable thermal conductivity: Entropy generation analysis

The study of hybrid nanofluid flow bounded by double-revolving disks is crucial due to its significant applications in enhancing heat transfer in various industrial processes, including cooling systems, lubrication technologies, and energy storage systems. This manuscript presents an entropy generation analysis of the magnetohydrodynamic Darcy-Forchheimer flow of a non-Newtonian second-grade hybrid nanofluid between double-revolving disks with variable thermal conductivity. The hybrid nanofluid combines titanium dioxide (TiO2) and cobalt ferrite (CoFe2O4) nanoparticles in a base fluid of engine oil. Appropriate similarity transformations convert the dimensional equations governing the flow phenomena into a non-dimensional form. The resulting non-dimensionalized system of equations is then solved using the homotopy analysis method (HAM), a semi-analytical technique. The results are validated by comparing them with previously published work for a specific case of the present analysis, and they are found to be in very good agreement. A comprehensive parametric analysis is conducted to understand the behavior of flow and heat transfer to various physical parameters involved in the study. It was found that there is an enhanced heat transfer rate at both disks when the Reynolds number and titanium dioxide nanoparticle concentration are higher. It was also found that Bejan number declined with increasing Brinkman number.

Melting heat transfer of a quadratic stratified Jeffrey nanofluid flow with inclined magnetic field and thermophoresis

Recently, researchers are facing great challenges to form the homogeneous solutions of various liquids at biomedical and industrial levels. Such homogeneous solutions can be controlled through stratification phenomenon directly which is ignored by the researchers in the existing literature specifically quadratic stratification and melting heat mechanism which is valid only for higher temperature processes. Thus, to form the homogeneous and stable liquid solutions for various industrial processes, we investigate the melting heat phenomenon in quadratic stratified Jeffery Nano fluid flow deformed due to linearly stretching sheet along with stagnation point. Inclined constant magnetic field is implemented on the fluid through an arbitrary angel. Characteristics of heat and transportations are disclosed through viscous dissipation, Brownian motion and thermphoresis. Temperature and concentration of the surrounding fluids are assumed higher than the stretching surface. The resultant governing equations are reduced to ordinary differential equations through proper transformations. Convergent analytical series solutions are computed via homotopic approach. Impact of various emerging parameters on temperature, velocity and concentration fields are illustrated and discussed comprehensively. Sherwood and Nusselt numbers and drag force are scrutinized mathematically, physically and graphically. It is analyzed from the study that (i) dominant melting reduces the temperature field (ii) higher thermal and solutal stratification decay the temperature and concentration fields respectively (iii) higher thermophoresis enhances the temperature field. Further, it is concluded that stable and homogeneous solutions may be made by increasing melting and reducing stratification phenomena. This study will help us to provide actual amount of heat for heating processes in industries and biomedicine which is the basic requirement for excellent quality of products.

Influence of sedimentary structure and pore-size distribution on upscaling permeability and flow enhancement due to liquid boundary slip: A pore-scale computational study

Low-permeability sedimentary formations, such as tight sandstones, exhibit fluid flow and transport phenomena distinct from those in conventional porous systems due to the dominance of micro- to nanometer-sized pores and variable amounts of boundary slip. The widely used traditional no-slip boundary condition often fails to accurately describe fluid behavior in these formations. A knowledge gap exists in understanding how liquid slip influences fluid dynamics in complex, heterogeneous sedimentary structures, as previous studies have primarily focused on simplified, homogeneous pore geometries. In this study, we investigated the impact of boundary slip on low-Reynolds number fluid dynamics within synthetically designed two-dimensional graded and random pore networks with varying pore-size distributions to account for heterogeneity. Our results showed that velocity variance increased with increasing heterogeneity, following a power-law relationship. The power-law exponents decreased with boundary slip, quantifying how boundary slip mitigated the impact of heterogeneity on velocity variance. We developed a theoretical model to predict asymptotic flow enhancement and derived constitutive relations to estimate the coefficient C and maximum flow enhancement (ΔE) based on the pore-to-grain size ratio and porosity. Energy dissipation increased with both heterogeneity and boundary slip, which we identified as the primary mechanism contributing to asymptotic flow enhancement. This relationship was illustrated by a 1:1 linear correlation between maximum energy dissipation and maximum flow enhancement, regardless of heterogeneity, indicating that energy dissipation due to boundary slip entirely controls the emerging fluid dynamics. The presented theoretical model and constitutive equations offer practical applications for optimizing fluid dynamics in heterogeneous formations.

Numerical study of magneto-hydrodynamics natural convective flow in a porous-corrugated enclosure using a higher-order compact finite difference scheme

This study explores the numerical investigation of two-dimensional natural convection in a porous corrugated enclosure with heat sources of different heights and electrically conducting fluids. The governing equations are solved using a higher-order compact finite difference scheme. Boundaries on the top and sides are subject to thermal cooling and adiabatic conditions, respectively. Numerical results are presented for wide range of Rayleigh (103 to 106), Darcy (10−5 to 10−1), Hartmann (25 to 150), and Prandtl (0.015 to 10) numbers. For fixed high Rayleigh-Darcy values, the porous medium has higher permeability. Most significant possible multiple steady solutions can be found in the case 1 at Ra=106,Da=10−2,Ha=50, and Pr=10.0. In the low to moderate critical values of Prandtl numbers, it encompasses a wide range of fluid flow phenomena, from stable to unstable. The maximum enhancement of the averaged Nusselt numbers on the boundaries in increasing and decreasing trends are viz. Ra(139.13% and 54.37%), Da(46.14% and 74.25%), Ha(633.04% and 74.73%), and Pr(142.52% and 45.92%) for case 1, Ra(129.64% and 0.32%), Da(40.68% and 69.66%), Ha(46.65% and 80.85%), and Pr(18.41% and 18.23%) for case 2, and Ra(163.98% and 77.20%), Da(8.25% and 58.68%), Ha(81.38% and 59.17%), and Pr(30.60% and 22.46%) for case 3.

Impact of nanopore confinement on phase behavior and enriched gas minimum miscibility pressure in asphaltenic tight oil reservoirs

Miscible gas injection in tight/shale oil reservoirs presents a complex problem due to various factors, including the presence of a large number of nanopores in the rock structure and asphaltene and heavy components in crude oil. This method performs best when the gas injection pressure exceeds the minimum miscibility pressure (MMP). Accordingly, accurate calculation of the MMP is of special importance. A critical issue that needs to be considered is that the phase behavior of the fluid in confined nanopores is substantially different from that of conventional reservoirs. The confinement effect may significantly affect fluid properties, flow, and transport phenomena characteristics in pore space, e.g., considerably changing the critical properties and enhancing fluid adsorption on the pore wall. In this study, we have investigated the MMP between an asphaltenic crude oil and enriched natural gas using Peng-Robinson (PR) and cubic-plus-association (CPA) equations of state (EoSs) by considering the effect of confinement, adsorption, the shift of critical properties, and the presence of asphaltene. According to the best of our knowledge, this is the first time a model has been developed considering all these factors for use in porous media. We used the vanishing interfacial tension (VIT) method and slim tube test data to calculate the MMP and examined the effects of pore radius, type/composition of injected gas, and asphaltene type on the computed MMP. The results showed that the MMP increased with an increasing radius of up to 100 nm and then remained almost constant. This is while the gas enrichment reduced the MMP. Asphaltene presence changed the trend of IFT reduction and delayed the miscibility achievement so that it was about 61% different from the model without the asphaltene precipitation effect. However, the type of asphaltene had little impact on the MMP, and the controlling factor was the amount of asphaltene in the oil. Moreover, although cubic EoSs are particularly popular for their simplicity and accuracy in predicting the behavior of hydrocarbon fluids, the CPA EoS is more accurate for asphaltenic oils, especially when the operating pressure is within the asphaltene precipitation range.

Shock–shock interaction on the Reusability Flight Experiment (ReFEx)

AbstractThe Reusability Flight Experiment (ReFEx) is currently under development at the German Aerospace Center (DLR). A coupled experimental and numerical campaign was carried out to investigate the surface heating on the payload geometry during return consisting of a forebody and canard. In this way, numerical tools for a post-flight analysis can be preemptively improved where required. Experiments were undertaken at the High Enthalpy Shock Tunnel Göttingen (HEG) on a 1:4 scale model with the use of temperature sensitive paint on the payload geometry to obtain surface heat flux. The model configuration was varied in angle of attack and canard deflection. Laminar and turbulence-model solvers in the DLR-TAU code were used for the numerical simulations. This investigation focussed on the shock–shock interaction of the nose bow shock with the leading-edge shock of the canards showing significant surface heat flux along the canard. Larger surface heat fluxes were measured in the experiments downstream of the shock interaction on the canard, than obtained from the laminar CFD calculations. This was attributed to transition of the boundary layer within the interaction regions, in the presence of significant adverse pressure gradients. Other flow features along the forebody in the vicinity of the canard were qualitatively matched better by the fully-turbulent numerical solutions than the laminar ones. This work aims to demonstrate the extent to which the numerical and experimental tools assist useful insights into flow phenomena during the return stages of the ReFEx payload geometry, and the aspects for which improvements are required.

The Influence of the Geometry of Grooves on the Operating Parameters of the Impeller in a Centrifugal Pump with Microgrooves

Centrifugal pumps are one of the most widely used machines in all branches of industry. For this reason, their efficiency has a significant impact on energy consumption in global industry (about 20%). It is extremely difficult to design low-specific-speed centrifugal pumps at acceptable efficiency levels due to increasing losses in the impeller (hydraulic, volumetric, and mechanical). This article presents the influence of the geometric features of grooves (width, depth), and the number of them, on the operating parameters of the impeller in a centrifugal pump with microgrooves. The principle of operation of this solution involves the passive control of the flow in the boundary layer using rectangular grooves. The grooves are made inside the flow channels of the impeller and are intended to reduce hydraulic losses occurring during flow. This is mainly due to a reduction in losses in the boundary layer. In order to determine the influence of the grooves’ parameters on the energy characteristics of the impeller, numerical calculations and experimental measurements were performed on 15 sets of impellers, which were obtained using experimental planning methods. The CFD calculations were conducted in order to understand the flow phenomena that occur in the impeller with the microgeometry and their effect on a reduction in internal flow losses. Based on the research results, useful guidelines for designing impellers with low-speed characteristics were formulated.