Aerodynamic Process Research Articles

Aerodynamic development of the BYD SEAL – Part 2: Overview

BYD SEAL is a new developed A+ class sedan by BYD Auto, based on third generation high-performance and high-safety electric platform for EVs. SEAL gives full play to the advantages of electric vehicles in terms of space, handling, NVH, etc., while striving to reach the same level of fuel vehicles in terms of cost and recharge mileage. Therefore it has been dedicated to minimizing energy consumption from all components since its inception, and an important one is to reduce the aerodynamic drag effectively. However, the “ocean aesthetics” styling design based on the original concept model and platform with short overhangs must be kept on this car, which brings great challenge to aerodynamic development. An adaptable aerodynamic development process is set up and correlation between CFD simulation and wind tunnel test are established. This paper depicts the features of the flow field determined in the aerodynamic development process of the BYD SEAL, and describes the key factors in aerodynamic drag reduction as a full model change in detail. Effective rear roofline angle, tail design, front bumper corners, underbody, wheel, detail management such as sealing loss are studied and optimized by Powerflow and Star-CCM+ simulation softwares, and verified in wind tunnel tests of full-scale clay models and prototype vehicles. Design fusion and development tool/efficiency improvement around the vehicle are established, and the inherent drag reduction mechanism is revealed. These findings are of great significance to the aerodynamic optimization with diverse aesthetic and engineering requirements under the background of EV platformization.

Aerodynamic optimization of multi-stage axial turbine based on pre-screening strategy and directly manipulated free-form deformation

To address the challenges of multiple design variables, long evaluation times, and poor global search capability of traditional surrogate-assisted algorithms that rely on the complete substitution of accurate function evaluations in the turbine aerodynamic optimization process, a pre-screening surrogate-assisted elitist preservation genetic algorithm (pre-SAEGA) optimizer is proposed. Pre-screening strategy in the pre-SAEGA can screen samples instead of directly estimating them, thereby reducing expensive evaluations in each generation. The directly manipulated free-form deformation (DFFD) method is applied to parameterized multi-stage axial turbines, and multi-degree-of-freedom flexible control is realized. Combining the pre-SAEGA with the DFFD method, a data-driven multi-stage axial turbine optimization platform is established. A two-stage axial turbine is the research object, and 44 design variables are selected for the combined optimization design of flow path and blade rows. The results show that the isentropic efficiency and flow rate improve by 1.33 % and 1.81 % respectively, and the pressure ratio decreases by 0.47 % at the turbine design point. The presented optimization platform not only improves the aerodynamic optimization effect but also significantly reduces the number of design variables and real evaluation samples, making it suitable for solving multi-stage turbine optimization problems with multiple degrees of freedom.

Aerodynamic resuspension of irregular flat micro-particles

This study investigates the role of particle shape on the aerodynamic resuspension process of irregular flat micro-particles on a substrate. We propose that these particles resuspend at higher velocities than spherical ones of the same size under the same aerodynamic forces. Two sets of data are analyzed to test the argument, the first from experiments we conducted using crushed glass particles (ranging from 80 μm to 300 μm) and the second from published data on RDX explosive residue particles (sized between 10 μm and 25 μm) published previously.We particularly analyze the shape factors of the particles used in the experiments and introduce them into a Monte Carlo (MC) simulation model. The probabilities for the time evolution of the resuspension process are calculated through a Markov chain of states. The transition probabilities entail the balance between the forces and moments involved in the mechanisms for particle detachment from the surface.The particle resuspension rate as a function of the fluid velocity is evaluated both experimental and numerically. Additionally, we assess the removal efficiency for different particle size ranges whenever possible.Both experimental and numerical results demonstrate that the resuspension fraction of irregular flat particles is significantly lower than for equally sized glass microspheres under the same conditions. Simulations corroborate previous experimental findings, indicating that smaller irregular particles exhibit higher removal efficiency. According to the MC model results, irregular particles detach by sliding rather than rolling.

Aerodynamic breakup of gel suspension droplets loaded with aluminum particles

The persistent and frequent space explorations are affected by the performance of propellants, among which the closely related gel propellants have been widely used due to their unique characteristics. Currently, research efforts primarily concentrate on the metallization and atomized combustion of gel propellants, emphasizing the combustion performance of metallized gel propellants. However, little attention has been given to the secondary breakup process that occurs just before combustion. By utilizing high-speed flow visualization technology, this study examines the key aerodynamic breakup process of gel suspension droplets loaded with micro aluminum particles, experimentally and theoretically investigating the droplet dynamics induced by particle volume fraction. The experimental confirmation of the three breakup behaviors exhibited by gel suspension droplets, namely oscillation mode, bag-stamen breakup, and hemline breakup, is presented along with the construction of a phase diagram. The impact of heterogeneous effects resulting from an increase in particle volume fraction on the critical breakup Weber number is revealed, with a concentration of 9 % as the turning point. Within the range of moderate Weber numbers, the tail flick deformation of suspension droplets in airflow is observed and reported for the first time. At different particle concentrations, there keeps a linear correlation between the dimensionless tail length and Weber number. Spherical suspension droplets will deform into thin disks in the airflow, with a nearly constant deformation rate regardless of changes in particle concentration. Additionally, the relationships between characteristic times and droplet parameters are discussed through statistical analysis of the results. As Ohnesorge number and particle volume fraction increase, the characteristic times both show a monotonically increasing trend. Moreover, a model of unstable growth rate associated with the particle volume fraction is established through linear instability analysis, accurately predicting the variation in critical Weber number for gel suspension droplet breakup. The congruence between our theoretical framework and experimental findings not only enhances comprehension of the impact of micro aluminum particles on the secondary breakup of gel suspension droplets but also provides valuable guidance for the aerospace applications of metallized gel propellants.

Thermal modal analysis of hypersonic composite wing on transient aerodynamic heating

Considering the influence of thermal stress and material property variations, this study employs the Navier–Stokes equations and Fourier heat conduction law to establish a semi-implicit time-domain numerical analysis method for hypersonic aerothermal-structural coupling. Study the temporal variation pattern of different regions of the composite material wing under aerodynamic heating. Using the obtained transient temperature field of the wing, the thermal modal of the wing at different time points is calculated using the finite element method. Additionally, it conducts an analysis and discussion on the factors influencing the thermal modal. Composites can be effectively utilized as thermal protection materials for aircraft. During the aerodynamic heating process, the leading edge temperature reaches thermal equilibrium first, followed by the trailing edge, and the belly plate experiences a slower thermal response. Temperature rise significantly affects higher-order modes, with the change in material properties during the early stages of heating being the dominant factor. This leads to a faster decrease in natural frequency. As heat conduction progresses, the influencing factors of thermal stresses gradually increase, and the natural frequency decreases slowly or even rises.

A rapid method for turbomachinery aerodynamic design and optimization using active subspace

Preliminary design is a crucial step in the turbomachinery aerodynamic design process, which involves the initial conceptualization and serves as the foundation for subsequent detailed design and analysis. During preliminary design, designers typically use a combination of empirical correlations, simplified flow models, and computational tools to evaluate the impact of different design parameters on the machine’s performance. This iterative process heavily relies on the designer’s experience and knowledge, and errors made during preliminary design may not be rectifiable in later design phases. To address this challenge, this paper proposes a novel optimization strategy for turbomachinery aerodynamic preliminary design using active subspace. The method utilizes active subspace techniques to reduce the dimensionality of the design space, making efficient and accurate exploration of the space possible. In addition, the open-access <italic>Multall</italic> turbomachinery design suite is employed to evaluate the aero-thermal performance of different designs. The method was then utilized to optimize the aerodynamic design of the blade profile for a ducted fan. Results show that the optimization strategy can identify the most significant directions in the design space, providing designers with a clear path to achieving an optimal design. Overall, the proposed method can be of good value to the turbomachinery design community attribute to its reduced dependence on the designer’s experience and elevated efficiency of the design process.

Manifold-guided multi-objective gradient algorithm combined with adjoint method for supersonic aircraft shape design

The aerodynamic design of supersonic aircraft necessitates the comprehensive consideration of multiple conflicting design objectives and multi-disciplinary characteristics. However, the efficiency of heuristic algorithms in solving multi-objective aerodynamic problems significantly decreases with the increase in the number of design variables and objectives. Although gradient-based adjoint optimization methods can eliminate the constraints of design variables on aerodynamic optimization and have high optimization efficiency, they are prone to getting stuck in local optima and are difficult to apply in multi-objective optimization. To overcome these shortcomings, a manifold-guided multi-objective gradient-based algorithm (MG-MOGBA) is proposed. This algorithm enhances the optimization efficiency of the algorithm by coupling the multi-objective gradient operator with the predicted Pareto front (PF) manifold structure to guide the population search direction and reduce the search space. A multi-objective aerodynamic optimization framework based on the discrete adjoint method is developed to automate the aerodynamic optimization process. Test functions and airfoil optimization results confirm that the proposed algorithm achieves superior results with fewer iterations and is more efficient than heuristic algorithms. The four-objective supersonic civil aircraft example demonstrates that the algorithm can effectively handle high-dimensional multi-objective aerodynamic optimization problems. A potential equilibrium solution increased the cruise factor by 17.5% and 12.8% under supersonic and transonic conditions respectively, reduced the maximum overpressure of the sonic boom by 25.1%, and decreased the root bending moment by 20.3%. Overall, MG-MOGBA can efficiently solve high-dimensional multi-objective aerodynamic optimization problems and has good scalability for the dimensions of design objectives and variables.

Experimental Investigation on the Aerodynamic Instability Process of a High-Speed Axial-Centrifugal Compressor

Abstract Aerodynamic instability plays an important role in compressor design and may cause performance degradation and fatigue damage. In this paper, an experimental study on the evolution of aerodynamic instability is carried out on a compressor that combines the performance benefits of an axial stage and centrifugal stage. The spatiotemporal characteristics of unsteady wall pressure were obtained using fast-responding pressure transducers over a range of operating conditions. The results show that the axial stage works on the positive slope of the performance characteristic curve from choke to stall at low-speed operating conditions, and mainly features rotating instability. Rotating stall is also observed in the impeller (IMP) and diffuser passages. At medium-speed operating conditions, the centrifugal stage suffers a high-frequency mild surge, alternating with rotating stall. With the increase in back pressure, the mild surge diminishes, and rotating stall persists. This behavior is similar to a two-regime-surge, which has been reported for centrifugal compressors. At high-speed operating conditions, the compressor directly reaches surge without other instabilities. Further analysis of the spatial pattern of the rotating stall revealed the existence of a high-pressure region near the volute tongue, resulting in obvious pressure distortion along the circumferential direction at the volute inlet. This induced the amplitude difference of stall cells in corresponding diffuser passages. The disturbance caused by stall cells propagates upstream through the blade passage, and the largest pressure disturbance induced by the stall cell propagation appears in a circumferential position 45 deg downstream of the volute tongue at the impeller inlet and the axial stage inlet.

Gas Kinetic Scheme Coupled with High-Speed Modifications for Hypersonic Transition Flow Simulations.

The issue of hypersonic boundary layer transition prediction is a critical aerodynamic concern that must be addressed during the aerodynamic design process of high-speed vehicles. In this context, we propose an advanced mesoscopic method that couples the gas kinetic scheme (GKS) with the Langtry-Menter transition model, including its three high-speed modification methods, tailored for accurate predictions of high-speed transition flows. The new method incorporates the turbulent kinetic energy term into the Maxwellian velocity distribution function, and it couples the effects of high-speed modifications on turbulent kinetic energy within the computational framework of the GKS solver. This integration elevates both the transition model and its high-speed enhancements to the mesoscopic level, enhancing the method's predictive capability. The GKS-coupled mesoscopic method is validated through a series of test cases, including supersonic flat plate simulation, multiple hypersonic cone cases, the Hypersonic International Flight Research Experimentation (HIFiRE)-1 flight test, and the HIFiRE-5 case. The computational results obtained from these cases exhibit favorable agreement with experimental data. In comparison with the conventional Godunov method, the new approach encompasses a broader range of physical mechanisms, yielding computational results that closely align with the true physical phenomena and marking a notable elevation in computational fidelity and accuracy. This innovative method potentially satisfies the compelling demand for developing a precise and rapid method for predicting hypersonic boundary layer transition, which can be readily used in engineering applications.

Numerical and physical modeling of the aerodynamic process in a direct-flow coil-type boiler using a laboratory stand

The article examines the modes of gas passage through the chimney of a direct-acting steam generator set using a laboratory stand made of a cylindrical coil. The criterion for determining the gas flow regime is a dimensionless quantity called the Reynolds number. The air flow velocities and temperatures were determined experimentally. Based on these results, the Reynolds number was calculated and the flow regimes at each measurement point were determined, and the dependence of the Reynolds number on temperature and velocity was obtained, and the experiment was analyzed. With the help of the ANSYS program, a model of air movement on the stand was built. When deciphering the geometric model, the ANSYS SpaceClaim program was used. The model made it possible to estimate the distribution of the air flow velocity in the boiler model based on experimental values. Further, after constructing a geometric model using the ANSYS Icem CFD program, a dispersion model was cre-ated that showed the temperature distribution of flue gases in the external gas flow of the basic model of a direct-flow steam boiler. The processing of experimental data showed a further prospect of intensification of the heat exchange process in a direct-flow steam boiler of the coil type.

Applicability of Drag Equation on a Dimpled Golf Ball using Changing Wind Velocities

The drag equation is commonly used to relate the resistance force experienced by an object traveling through fluids with its velocity. The pattern might vary based on the specific geometry of the objects (e.g., a dimpled golf ball). The dimples are known to reduce the amount of drag during the ball’s flight through a series of complex aerodynamic processes. To investigate the ball’s drag pattern, pressure and air velocity on the golf ball, a CFD using Ansys fluent is performed to simulate its aerodynamic features under nine different wind velocities. After the experiment, it was found that the relationship between the drag and velocity of the dimpled golf ball still generally conforms to the drag equation. The pressure and velocity distributions are consistent with the hypothesis, while the aerodynamic details are presented. The effect of dimples is also visualized, contributing to the flow demonstration. The investigation is valuable because the aerodynamic process of the dimpled sphere structure in changing wind velocities is well presented and analyzed, and it inspires further explorations on the aerodynamic effects of the dimple geometry.

Surge Process of a High-Speed Axial–Centrifugal Compressor

The surge is a typical aerodynamic instability phenomenon in the compression system, which can lead to serious consequences such as engine performance degradation and structural damage. A deep understanding of the surge process can support the development of a compressor with a wider operating range. In this paper, an experimental study was carried out and high-responding pressure sensors were used to obtain the aerodynamic instability process and the post-surge characteristics of an axial–centrifugal compressor at design and off-design speeds. The evolution of the flow field and instability behavior before and after the surge were analyzed. The results showed that the inlet temperature change can reflect the aerodynamic instability to some extent, and as the operating condition moves from the choke to surge boundary, the inlet temperature undergoes a sudden increase at a certain condition and further increases with the decrease in mass flow rate. At the design speed, the instability of the combined compressor featured a deep surge with an obvious rotating stall behavior before its inception, and the amplitude of the stall cell was gradually enhanced, finally leading to the surge. At the off-design speed, affected by the stage mismatching, the axial stage mainly worked near the unstable operating condition. Therefore, the compressor successively experiences two modes of mild surge and deep surge, and the rotating stall can also be observed during the surge cycle.

Research on aerodynamic shape optimization of reentry vehicle based on hybrid scale multi-fidelity neural network model

The mechanical expanded reentry vehicle has gained significant attention as a reliable solution for shuttle transportation and deep space exploration missions. However, the aerodynamic characteristics of such a reentry vehicle, including high dimensionality, strong nonlinearity, and parameter coupling, pose a challenge in achieving a balance between precision and efficiency in aerodynamic shape design. In this paper, we propose a hybrid scale multi-fidelity neural network (HS-MFNN) model by integrating low-fidelity and high-fidelity models with neural networks. This model is applied to optimize the aerodynamic shape of the reentry vehicle, addressing the challenge. The feasibility of applying the HS-MFNN model was validated through testing using the MBR function. The advantages of the HS-MFNN model were highlighted through a comparison with other models. Subsequently, the model was utilized in the aerodynamic optimization process of the reentry vehicle. The prediction error for the drag coefficient (Cd) was less than 1%, and for the head stagnation heat flux (QO), it was within 6%. Moreover, the computation time was reduced by three orders of magnitude, ensuring both computational accuracy and efficiency. After optimization, the Cd increased by 5.08%, while the QO decreased by 8.62%. These improvements demonstrate that the use of the HS-MFNN model significantly enhances the aerodynamic performance of the reentry vehicle. Consequently, the HS-MFNN model exhibits great potential for fast and efficient optimization processes.

An evaluation model for wall heat transfer effects on micro centrifugal compressors and its application in aerodynamic design

In micro gas turbine generators, the significant temperature difference within close proximity of the hot and cold components induces a substantial heat influx into the micro centrifugal compressor. This heat influx profoundly modifies the aerodynamic characteristics of the compressor. Ensuring a precise evaluation of the performance decline attributable to wall heat transfer effects and systematically integrating these impacts into the aerodynamic design process assumes paramount importance. Previous evaluation models, which involved unnecessary simplifications, suffered from limitations in accuracy. This paper presented a novel evaluation model for the diabatic isentropic efficiency through entropy analysis of the diabatic ideal compression process and the actual compression process. The rigorous theoretical derivation without any simplification empowers this model to faithfully mirror the authentic aerodynamic performance of diabatic compressors. The experimental and numerical verification results indicate that the proposed model is more reliable than the previous ‘preheating-adiabatic compression’ model when evaluating performance degradation stemming from wall heat transfer. The new model exhibits an error of approximately 3.7% at the design point and a mean absolute error of about 6% along the characteristic line of the design speed. Both deviations are deemed acceptable within the purview of engineering assessments. Furthermore, this paper illustrated an instance of the novel model’s application in the aerodynamic design process. A prototype compressor, impeccably designed under adiabatic conditions but falling short of performance benchmarks during the performance test, was redesigned using the proposed method. The experimental results show that through the incorporation of wall heat transfer effects, the redesigned compressor aligns perfectly with design requirements, yielding an efficiency enhancement of roughly 1.5%.

Aerodynamic performance of low aspect-ratio flapping wing with active wing-chord adjustment

In daily life, excellent aerodynamic performance of birds and bats has been widely observed during their flying and propulsion. In the present research, a low aspect-ratio wing flapping in uniform flow with a combined heaving-pitching motion has been adopted to mimic such aerodynamic process of flapping-wing-based propulsors. Inspired by the changeable skeleton of natural bio-livings, a bio-inspired flow controlling strategy based on active wing-chord adjustment has been raised to achieve aerodynamic enhancement. Adopting an Immersed Boundary-Lattice Boltzmann Method (IB-LBM) to resolve relating fluid flow with moving boundary, the effects of stretching pattern, i.e., the amplitude and the phase of the wing-chord adjustment, on the aerodynamic performance of the wing, and the role of Aspect-Ratio (Ar) have been confirmed and investigated in detail. With the Direct Numerical Simulation to achieve the vortical flow identification, detachment delaying of Leading Edge Vortex (LEV) and enhancement of Trailing Edge Vortex (TEV) have been observed for cases with in-phase active controlling, and it has been revealed that such phenomenons correlate well with the aerodynamic enhancement of the wing. On the other hand, it has been observed that, the out-phase wing-chord adjustment dominates the LEV detachment, and further the flow separation around the leading edge of the wing. It is believed that such flow detachment, together with the TEV weakening caused by the anti-phase wing-chord controlling, leads to the performance deterioration of the wing, compared with the in-phase case. Meanwhile, the present numerical results show that, with the increase of stretching ratio, the aerodynamic performance of the flapping wing becomes susceptible with respect to the stretching phase of wing-chord. Compared with the bounded thrust enhancement caused by the LEV bursting, the lifting enhancement of the flapping wing during the reinforced wing-chord adjustment shows consistent dependency on the stretching ratio.

RESEARCH OF THE AERODYNAMIC PROCESS OF CARBON DUST REMOVAL FROM THE WORKING ZONE

The purpose of this work is research of the aerodynamic process of carbon dust removal from the working zone in order to create safe and harmless working conditions at the production site. As a result of the research, an aerodynamic calculation of a long air duct of uniform suction with tangential air intake was performed. The degree of twisting of the air flow inside the air duct, as well as the uniformity of air suction along the length of the long suction, were determined. A number of factors affecting the dust removal process have been established, such as suction torch long suction; coefficient of local suction resistance; forces of inertia and viscosity on the resistance of local suction. The dependence of the ratio of the width of the entrance hole to the diameter of the air duct on the local suction resistance, the dependence of the ratio of the areas of the entrance gap and the cross section of the transitional air duct on the local suction resistance, as well as the effect of the length of the entrance slot on the coefficient of local suction resistance were determined. The efficiency of suction of dust particles with an extended suction unit with tangential air entry has been proven. For a more accurate analysis of the distance at which an extended extractor with tangential air intake can be placed relative to the dust source, it is necessary to conduct a dispersed dust analysis. For effective capture of specific dust, calculations should be based on the size of the dust, which occupies a larger share in the distribution of fractions. The smaller the dust particle, the further the suction device can be located. To visualize the experimentally obtained results, simulation was performed in the FlowVision software in accordance with the mathematically calculated initial data. During the simulation of the movement of dusty air in an extended extractor with a tangential entry into the system, the occurrence of swirling of the air flow has been proven. Due to this formation, the largest fractions of dust will move along the walls of the air duct. This makes it possible to use extended extractors to remove coarse fractions of dust contained in polluted air, organizing the removal of air moving near the walls of the air duct. Keywords: carbon dust, aerodynamic calculation, engineering simulation, occupational diseases, occupational health.

CFD approach to predict the significance of the shape bluff body on flame stabilisation in lean premixed combustion of hydrogen-air mixtures

Over the past two decades, Europe, particularly France, has put a lot of effort into further developing information on supersonic air-breathing including Ramjet and Scramjets, providing first-part design techniques, and facilitating the necessary innovations. In actual ramjet-powered missiles, free stream air enters the inlet of a ramjet which goes through the aerodynamic compression process called “Ram Compression”. This process increases the static temperature of the air. To get the higher temperatures caused by streamlined compression for realistic simulations on the ground, an air warming framework must be organised at the test site. Using an Air vitiator or a mix of vitiator and electric heaters is the best approach to generate temperature change that resembles flying conditions on the ground. The fuel selected is Hydrogen, which is further supplied with makeup oxygen to maintain the molecular percentage of oxygen. A variety of air heater chamber configurations with various flame stabilisation methods are evaluated. A validated FLUENT CFD Code using species transportation is used to investigate to model the burning of the air heater. The ignition characteristics and fire consistency of a lean premixed hydrogen-air combination in a combustor with diverse mathematical designs of the bluff body under unique physical and chemical constraints have been examined by settling a two-dimensional mathematical plan. The air vitiator structure is good for giving air at temperature scope of 400–1000 K, the strain between 20 and 35 bar at Mach numbers between 0.1 and 0.5, and an air mass stream pace of a reasonable amount. Sample air vitiator's performance parameters and design calculations for connect mode ramjet test facility are formulated in the paper.

Aerodynamic Data-Driven Surrogate-Assisted Teaching-Learning-Based Optimization (TLBO) Framework for Constrained Transonic Airfoil and Wing Shape Designs

The surrogate-assisted optimization (SAO) process can utilize the knowledge contained in the surrogate model to accelerate the aerodynamic optimization process. The use of this knowledge can be regarded as the primary form of intelligent optimization design. However, there are still some difficulties in improving intelligent design levels, such as the insufficient utilization of optimization process data and optimization parameters’ adjustment that depends on the designer’s intervention and experience. To solve the above problems, a novel aerodynamic data-driven surrogate-assisted teaching-learning-based optimization (TLBO) framework is proposed for constrained aerodynamic shape optimization (ASO). The main contribution of the study is that ASO is promoted using historically aerodynamic process data generated during the gradient free optimization process. Meanwhile, nonparametric adjustment of the TLBO algorithm can help relieve manual design experience for actual engineering applications. Based on the structure of the TLBO algorithm, a model optimal prediction method is proposed as the new surrogate-assisted support strategy to accelerate the ASO process. The proposed method is applied to airfoil and wing shape designs to verify the optimization effect and efficiency. A benchmark aerodynamic design optimization is employed for the drag minimization of the RAE2822 airfoil. The optimized results indicate that the proposed method has advantages of high efficiency, strong optimization ability, and nonparametric characteristics for ASO. Moreover, the results of the wing shape optimization verify the advantages of the proposed methods over the surrogate-based optimization and direct optimization frameworks.

A novel pneumatic structure for reducing train-induced mass and heat transfers in a permafrost tunnel

As a train passes quickly through a confined space such as a tunnel, it induces dramatic airflow movement in the tunnel. The substantial mass transfer results in a noteworthy energy transfer in the air-tunnel system, forming complex aerodynamic and thermodynamic processes (ATPs). The aerodynamic process has been studied well enough to solve many practical engineering issues. However, little attention has been given to the thermodynamic process in tunnels, especially heat transfer in permafrost tunnels. To study the train-induced mass and heat transfers in the Fenghuoshan permafrost tunnel and design a novel pneumatic structure (PS) to mitigate thaw damage to the tunnel, we built a train-induced mass-heat transfer (MHT) model for permafrost tunnels based on mass, momentum and energy conservation and simulated the ATPs in tunnels without and with the PS. By comparing the mass and heat transfers in the two tunnel structures, we found that the air temperature maximally increases by 1.7 °C in the tunnel without the PS, whereas it increases by only 0.5 °C in the tunnel with the PS. In addition, the PS also reduces the convective heat transfer coefficient (CHTC) by 38.6 % compared with that of the tunnel without the PS. Therefore, the PS can significantly decrease the temperature rise in the tunnel system and prevent excess heat energy from penetrating into the surrounding permafrost. Consequently, it is an efficient method for mitigating thaw damage to permafrost tunnels. Moreover, the study is also helpful for comprehending train-induced mass and heat interactions in permafrost tunnels.

A comparative study on the microstructure development in Fe50Cu50 alloy prepared using aerodynamic levitation process and W-wire held process

The present lays emphasis on the effect of varying degrees of undercooling on the microstructure development of the Fe50Cu50 alloy system. A sufficiently high undercooling (>100 °C) was achieved using the aerodynamic levitation (ADL) technique whereas a W-wire holding method in the same ADL setups was employed to attain relatively low undercooling (87 °C) during solidification. In addition, solidification experiments were also performed without any undercooling in this alloy system. Thus, the effect of a wide range of undercooling on the phase separation and microstructural development of the Fe-Cu system was systematically investigated in this work. In a substantially undercooled ADL sample, a complete phase-separated micrograph was obtained, but in other situations, a discontinuous network of Cu in interconnected Fe dendritic areas was detected as determined by the scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). X-ray diffraction (XRD) of the sample cross-section confirms that the phases present at the end of the solidification process are α-Fe and Cu, regardless of the degree of undercooling. In the instance of the ADL sample, the entrapment of Cu droplets in the inter-connected Fe dendritic area due to a combination of high undercooling and centrifugal force was detected using X-ray tomography, and the orientation distribution of the samples was determined using Electron Backscatter Diffraction (EBSD).