High-speed Airflow Research Articles

Enhanced high-temperature stability of indium tin oxide - Indium oxide thermocouples by two-step annealing

The complex internal structure of the aero-engine and the high-temperature, high-pressure, and high-speed airflow make it difficult to measure the internal temperature. Indium tin oxide (ITO) and In2O3 films have been studied for their application in high-temperature thermocouples and strain gauges. Due to their large Seebeck coefficient and high-temperature stability, ceramic thin-film thermocouples are expected to be used at high-temperature measure. In this paper, ITO-In2O3 thermocouples were fabricated by magnetron sputtering. Besides, the electrical properties of the air-annealed and two-step nitrogen-annealed thermocouples were compared, including the repeatability of thermoelectric response after multiple thermal cycles and the drift rate during the high-temperature duration. The microstructure and electrical conductivity of both the as-deposited and post-annealed ceramic thin films were tested respectively. The result shows that the resitivity and Seebeck coefficient of the thin films annealed in nitrogen is reduced, but the stability at high temperature is greatly improved.

Experimental Study on Flow and Heat Transfer Characteristics of Jet Array Impingement Combined with Kagome Truss Structures with/without Cross-flow

Jet array impingement providing high heat transfer are widely used in heat exchangers. However, the target plate is easily damaged impinged by high-speed air flow constantly. To solve this issue, Kagome truss structure is combined with jet array impingement to improve cooling performance in this paper. The flow and heat transfer characteristics of this composite structure in a heat exchanger unit with/without cross-flow were experimentally studied. Additionally, Kagome truss structures of circular and water-drop-shaped rods were used respectively in jet space and the results showed that the latter was beyond 7% higher than the former for the comprehensive thermal performance. When cross-flow was not added, the comprehensive thermal performance factor of the latter reached to a maximum of 1.656 at the Reynolds number of 5000. When cross-flow was added, the comprehensive thermal performance got worse at the cross-flow-to-jet velocity ratio of 1.0, while the best comprehensive thermal performances were found at the cross-flow-to-jet velocity ratio of 0.6 and at the mass flow rate proportion of cross-flow of 0.5, respectively. These results can provide a basic experimental data as a reference for designing new structures in advanced heat exchanger.

Effect of post-processing methods on the surface quality of Ti6Al4V fabricated by laser powder bed fusion

Ti6Al4V is widely used in aerospace and medical applications, where high demands on dimensional accuracy and surface quality require the application of post-processing to achieve optimal performance. However, the surface quality of parts fabricated by LPBF is inferior due to the inherent defects of LPBF. Therefore, it is important to investigate the effect of post-processing on the surface quality of Ti6A14V parts fabricated by LPBF. In this work, the effect of post-processing methods (i.e., sandblasting, electrolytic polishing, chemical polishing, and abrasive flow polishing) on the surface quality of Ti6Al4V fabricated by laser powder bed fusion (LPBF) additive manufacturing was investigated. The changes in surface roughness and morphology of the 45° inclined square and curved pipe Ti6Al4V samples processed with post-processing were observed, and the weight and elemental changes of the parts were also analyzed. The result reveals that sandblasting, electrolytic polishing, chemical polishing, and abrasive flow polishing are all effective in improving the surface quality of Ti6Al4V parts fabricated by LPBF. The effect of sandblasting is mainly caused by sharp-edged grit driven by high-speed airflow, resulting in the lowest surface roughness and the least influence on the weight, but may contaminate the surface with residual brown corundum. Electrolytic polishing and chemical polishing achieve surface quality improvement through different corrosion patterns without changing the surface composition. The surface smoothness of parts processed with chemical polishing is the best, while the weight loss rate of the sample processed with electrolytic polishing is the most at about 7.47%. Abrasive flow polishing presents a remarkable effect on polishing the internal surface of the Ti6Al4V sample by the extrusion scratching, extrusion deformation, and micro-cutting effects of abrasive on the surface. The findings can provide important engineering references for the post-processing of precision Ti6Al4V parts fabricated by LPBF and further promote the engineering applications of Ti6Al4V parts.

Investigation of Formation Process and Intensity of Coal and Gas Outburst Shockwave

The shock wave of a coal and gas outburst is a high-pressure and high-speed impact airflow formed rapidly after the outburst. The propagation destroys the ventilation facilities and causes the destruction of the ventilation system. The theoretical research on the outburst shock wave is of great significance. In order to deeply understand the formation mechanism of the outburst shock wave, this paper draws on the shock wave theory to theoretically analyze the microscopic formation process of the outburst shock wave. The main difference between the formation process of a coal and gas outburst shock wave and the formation process of a general shock wave is that the outburst shock wave has a solid–gas flow zone in the high-pressure zone. The calculation formulas of pressure, density, temperature and other parameters before and after the outburst shock wave are derived. After the outburst shock wave passes through, the pressure, temperature and density of the roadway air will change suddenly. The relationship expression between outburst gas pressure and outburst shock wave intensity is derived, which can reflect the role of pulverized coal in the formation process of a shock wave. In order to facilitate the understanding and calculation, the concept of equivalent sound velocity of coal-gas flow is proposed, and the direct calculation of the impact strength of a coal and gas outburst is attempted. This paper is helpful to improve the understanding of the essence of a coal and gas outburst shock wave. It is also of great significance to outburst disaster relief.

Experimental research on online monitoring of high temperature and high speed airflow ablation of quartz ceramic thermal protection structure using guided wave

Thermal protection structure (TPS) plays a key role in protecting hypersonic flight vehicles from harsh service environment and has been widely used. As a common ablative thermal protection material, quartz ceramic TPS realizes thermal insulation by generating ablation during the reentry phases. The structural state of quartz ceramic TPS therefore is of great importance to the service performance and safety of hypersonic flight vehicles, and shows an urgent need for structural health monitoring (SHM). However, the monitoring of real ablation of quartz ceramic structure is barely considered in the current study, let alone online monitoring under harsh service environment, which brings a great challenge to the implementation of reliable ablation monitoring. Aiming at online ablation monitoring of quartz ceramic structure, this paper performs experimental research by taking advantage of guided wave (GW)-based monitoring method. An ablation experiment and monitoring system is built to generate real ablation under high temperature and high speed airflow and perform GW monitoring. The maximal temperature of the system can reach about 2100 °C. The feasibility of ablation monitoring is verified by analyzing ablation-induced influence on GW signals. Gaussian mixture model (GMM) is adopted to combine with GW method to suppress the high temperature variation caused by uncertainty influence on GW signals during the ablation process, so that reliable monitoring of ablation can be realized. Experimental results show that online monitoring of ablation propagation of quartz ceramic structure under high temperature variation is achieved, which can be further used for ablation quantification evaluation.

Numerical simulation and experimental research of fiber motion in vortex spinning

The application of high speed air flow in the textile field represents the frontier development direction in this field. However, the coupling mechanism between air flow and fiber is extremely complicated which greatly limits the development and application of new textile technologies. For this reason, this research study is intended to focus on the common cutting-edge basic scientific problem of the air-flow-fiber coupling mechanism, the vortex spinning technology is taken as a breakthrough point for research. Three-dimensional numerical models of air flow in vortex spinning nozzle and a free-end fiber were established. The hybrid grids including the structured hexahedral grids and the unstructured tetrahedral grids were used to divide the air-flow computational region, the realizable κ- ε model was used to solve the turbulent characteristics of air flow, and the wall function method was used to solve the air flow in the near wall region. The displacement and deformation of a single free-end fiber under the action of the air-flow force was solved by the second-order nonlinear double asymptotic method and interpolation method. The dynamic twist process of a free-end fiber was simulated in three-dimensional space by taking into account the fiber characteristics, such as straightening, bending, and torsion. In addition, a high magnification microscope was used to observe the free-end fiber motion during the spinning process. The results show that the numerical simulation is consistent with the experimental observation, proving that dynamic numerical simulation can solve difficult problems in the unobserved dynamic twisting process, and this deepens the understanding of the spinning mechanism in vortex spinning.

Aeroelastic modeling and analysis of honeycomb plates in high-speed airflow with acoustic load and general boundary conditions

Aeroelastic modeling and analysis of honeycomb plates in high-speed airflow with acoustic load and general boundary conditions

Localized coupling effects and multiphysics modeling for the laser ablation behavior of composite structure subjected to high-speed airflow

When the composite structure is subjected to high-power laser irradiation and high-speed airflow, its ablation behavior presents significant localized characteristics and strong coupling effect. In this work, a coupled fluid-thermal-ablation model is developed to quantitatively investigate the localized coupling effects. Here a loosely coupled scheme with second order temporal accuracy is utilized to improve the coupling efficiency, and a high-quality mesh reconstruction method combining the Arbitrary Lagrange-Euler (ALE) algorithm and Radial Basis Function (RBF) interpolation algorithm is established to capture the moving boundary of the localized ablation pit with large deformation. The model is validated by simulating the laser ablation behavior of C/SiC composite plate subjected to the hypersonic airflow, and the predicted ablation pit profile shows a good agreement with the available experimental result. Analytical results show that as the evolution of the localized asymmetric ablation pit induces transformation of the flow regime from a closed pit flow to an open pit flow. Moreover, the flow regime transition would remarkably alter the localized flow characteristics, including the local static pressure and dynamic pressure, which in turn significantly affects the sublimation and mechanical erosion rates of C/SiC composite plate, respectively.

Dust dispersion during the pulse-jet cleaning process with the diffuser effect of the cartridge filter.

A special conical diffuser was presented and fixed on the top of the filter cartridge to improve the flow field. The existence of the diffuser can disperse the jet flow from the nozzle, and the high-speed airflow can act on more areas of the filter cartridge, including the top area of the filter cartridge. To improve the cleaning efficiency, the present study is aimed at optimizing the structure of the filter cartridge. The DPM model was used to simulate the dust dispersion process and the falling dust sedimentation from the filter under the action of the pulsed airflow. To validate the established model, the pressure values at the monitoring points were analyzed and compared with the related experimental results. It is found that the pressure values are consistent with the experimental results. Moreover, the installation distance and the size of the diffuser were studied and their influence on the dust distribution on the surface of the filter cartridge. It is found that the dust removal effect is relatively better when the installation distance is 90mm and the size radius is 25mm. The maximum dust concentration can be reduced by 15mg/m3. The present research results can provide theoretical guidance for the cleaning process of the filter cartridge and finally improve the dust-removal efficiency of the dust collector.

Влияние структуры течения газа в осесимметричном канале на формирование неоднородного температурного поля в наполнителе из твердого легкоплавкого материала

This paper presents a study of the interaction between high-speed airflow and the surface of a solid low-melting material in a flowing channel of a model body. Both numerical and experimental approaches are used to solve the problem, which allows one to perform a comprehensive analysis of the processes under study. Numerical simulation conditions correspond to aerodynamic tests in the experimental facility. The unsteady Reynolds-averaged Navier-Stokes (URANS) equations are used to describe a gas flow. When solving the problem, the coupled heat-transfer and turbulence are taken into account. The low-temperature gas-dynamic processes are considered, while the chemical reactions and phase transition are neglected. As a result of numerical simulations, the flow structure and regime in a flowing channel of the model are determined, as well as the pressure and temperature distributions in the near-wall region of a solid combustible material. The gas flow regime corresponds to an underexpanded jet flow with the separation of the boundary layer and the formation of the intense heat-transfer regions at the initial section of the flowing channel. According to the numerical simulation results, in aerodynamic tests with a Mach number of 6, the melting point is attained in the near-wall region of the solid combustible material (polyethylene, polyoxymethylene, and wax). Aerodynamic tests are carried out to validate the obtained results. Experimental results show that the variation in the flowing channel diameter in the thick-wall cylinder made of polyethylene and polyoxymethylene is induced by thermal expansion. In aerodynamic tests with a wax cylinder, the mass reduction and the fusion of the solid-gas interface are revealed.

Research on Transient Characteristics of Scramjet Engine during Starting Sequence

Transient characteristics of entire engine system affect control method of the engine system. A quasi-transient simulator called Hypersonic Engine Dynamic Simulator (HEDS) was developed for the purpose of analyzing the transient behavior of a scramjet engine system. The simulator was constructed using the volume junction method, which is a type of finite volume method, and was introduced with a parallel computing function using the MPI library. In this study, the transient characteristics at the starting sequence of a scramjet engine equipped with an expander cycle was analyzed. In the startup transient analysis, two factors (the time from high-speed airflow inflow to the main valve opening and the time from the main valve opening to ignition) that affect the system startup were focused. In addition, constraints on the system were set to evaluate results of the analysis. As a result, there existed cases in which the maximum rotational speed of the turbo pump was much higher than expected when the interval between the inflow of high-speed airflow and the opening of the main valve was increased. In addition, there was also a delay time between ignition and fuel temperature rise. Therefore, the time from the main valve opening to ignition should be as short as possible. In the control phase, it was necessary to manipulate those two factors appropriately in order to bring the system to a steady state in a short time. HEDS was found to be a very effective tool for understanding the behavior of the system at the operating point and constructing a control method.

Numerical Simulation of Seed-Movement Characteristics in New Maize Delivery Device

The delivery device is one of the key components in ensuring uniform grain spacing and achieving high-speed precision seeding. In this paper, a new type of high-speed airflow-assisted delivery device for maize is presented. The gas–solid flow in the delivery device was numerically studied by the coupling method of CFD and DEM. The influence of the structural parameters of the delivery device on the movement of the seeds and the airflow field was analyzed in detail. The matching relationship between the inlet-airflow velocity and the operating speed of the seeder was explored. The results show that the position of the intake seed chamber mainly affects the negative pressure in the distribution area of the mixing chamber. The increase in the shrinkage angle results in the decrease in pressure loss and the decrease in airflow velocity in the delivery chamber. As the diffusion angle increases, the airflow forms a stable straight jet flow and the airflow velocity in the delivery chamber increases. As the ejection angle increases, the bouncing degree of the seed decreases, thereby ensuring the consistency of the seed-ejection direction. The research results show that, when the intake seed chamber is located in the middle, the shrinkage angle is 70°, the diffusion angle is 30°, and the exit angle is 60°, the air-assisted delivery device has better performance. With the increase in inlet wind speed, the seed-ejection speed can also be increased according to a certain proportion, which can meet the requirements of zero-speed seeding and ensure the uniformity of seed spacing, providing a new seed delivery scheme. In the future, if invasive damage to the seed shell is guaranteed to be minimized in high-speed airflow, the new delivery device can meet the requirements of precision seeding under high-speed conditions.

Development of a high-speed bioaerosol elimination system for treatment of indoor air

We developed a high-speed filterless airflow multistage photocatalytic elbow aerosol removal system for the treatment of bioaerosols such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Human-generated bioaerosols that diffuse into indoor spaces are 1–10 μm in size, and their selective and rapid treatment can reduce the risk of SARS-CoV-2 infection. A high-speed airflow is necessary to treat large volumes of indoor air over a short period. The proposed system can be used to eliminate viruses in aerosols by forcibly depositing aerosols in a high-speed airflow onto a photocatalyst placed inside the system through inertial force and turbulent diffusion. Because the main component of the deposited bioaerosol is water, it evaporates after colliding with the photocatalyst, and the nonvolatile virus remains on the photocatalytic channel wall. The residual virus on the photocatalytic channel wall is mineralized via photocatalytic oxidation with UVA-LED irradiation in the channel. When this system was operated in a 4.5 m3 aerosol chamber, over 99.8% aerosols in the size range of 1–10 μm were removed within 15 min. The system continued delivering such performance with the continuous introduction of aerosols. Because this system exhibits excellent aerosol removal ability at a flow velocity of 5 m/s or higher, it is more suitable than other reactive air purification systems for treating large-volume spaces.

Model construction and validation of airflow velocity attenuation through pear tree canopies.

To investigate the airflow velocity attenuation inside pear tree canopies and the factors that influence its effect on air-assisted spraying, the relationship between the resistance of the canopies to airflow and airflow velocity inside the canopies was determined. At the same time, the theoretical model of airflow velocity attenuation in the canopy was constructed, in which the velocity attenuation factor k and the incoming velocity were the model input values, and the airflow velocity in the canopy was the model output value. Then, experimental verification of the theoretical model was completed. The determination test of airflow velocity inside canopies with three leaf area densities revealed that the error range between the established theoretical model and the experimental airflow velocity inside the pear tree canopy was 0.11-1.25 m/s, and the mean size of the model accuracy was 83.4% under various working conditions. The results revealed that the region from a depth of 0m to 0.3m inside the canopy was the rapid attenuation area of the airflow and that from 0.3m to 0.9m was the low attenuation area. Furthermore, they revealed that high-speed airflow could strongly disturb the outer branches and leaves, greatly changing the windward area of the canopy blades and thus affecting the accuracy of the model. By introducing a dynamic parameter of the canopy leaf windward area for model correction, the R2 of the model was above 0.9. Finally, validation of the model was performed in an air-assisted spraying operation in an orchard. This study can provide a theoretical basis for the regulation of airflow parameters of air-assisted spraying of pear trees.

Multi-Disturbance Observers-Based Nonlinear Control Scheme for Wire Rope Tension Control of Hoisting Systems with Backstepping

The objective of this paper is to pursue a wire rope control methodology for reducing the tension difference between two wire ropes of a hoisting system. As we know, complicated disturbances exist in the complex electro-hydraulic hoisting system, notably, some of these disturbances are coupled, such as high-speed airflow disturbances, structure vibrations and vibrations in flexible wire ropes. Furthermore, there are model errors in force modeling due to the Coulomb friction between two wire ropes and two moveable head sheaves in the real physical hoisting systems. To eliminate disturbances, two types of disturbance observers (DOs) are employed: a traditional disturbance observer (TDO) and a coupled disturbance observer (CDO), both of which are utilized to estimate and compensate for the Coulomb friction and coupled disturbances online. As a result, a nonlinear backstepping control scheme is presented with estimation values from the TDO and the CDO. The experiment’s results demonstrate the effectiveness of the proposed control methodology.

Применение моделей реального газа к задаче обтекания тела высокоскоростным потоком

The paper presents results of computational simulation of the high-speed airflow around an axisymmetric body using various models that include ideal gas described by the Mendeleev—Clapeyron equation, real gas described by the Redlich—Kwong equation and user model approximating the empirical data. The user model is characterized by its own program code for the two-parameter approximation of the air thermophysical properties and taking into account in this context changes accompanying dissociation phenomena occurring at high temperatures without simulating physical and chemical transformations in the multicomponent gas mixture. The purpose of this study is to evaluate differences in the gas-dynamic flow pattern, shock-wave structure and thermal loading of the streamlined body depending on selection of the medium model. The results obtained make it possible to conclude on the need to introduce the real gas user models to reduce the error of computational simulation and ensure correct estimation of the heat flows.

Simulation Study of the Transport Characteristics of the Ice Core in Ice Drilling with Air Reverse Circulation

Ice core drilling with air reverse circulation is a promising technology that uses high-speed airflow to transport the ice core from the bottom of the hole along the central passage of the drill pipe to the surface. Understanding how the ice core moves through the pipe is crucial for this technology in order to calculate the pneumatic parameters. In this paper, experimental study and the CFD dynamic mesh technique are used to analyze the ice core transport process and flow field characteristics. In order to prove the correctness of the dynamic mesh technique, the simulation results were verified with the experimental results, and it was found that all the simulation data were in agreement with the experimental data trend, and the maximum error was less than 10%. According to the study, once the ice core’s velocity reaches its maximum throughout the transport process, it does not change. The ice core’s maximum velocity increases with the diameter ratio and decreases with the length-to-diameter ratio, while eccentricity has no impact on the maximum velocity. When the air velocity reaches 21 m/s, the diameter ratio for the ice core with a length-to-diameter ratio of 2 increases from 0.80 to 0.92, and the maximum velocity increases from 8.92 m/s to 17.45 m/s. Data fitting demonstrates that the equation Vmax=−1.04V0 + 1.04Va describes the relationship between the ice core’s maximum velocity, Vmax, and air velocity, Va. Finally, we obtain the ice core’s suspension velocity model using CFD simulation to calculate the suspension velocity, V0.

Wind Resistance Mechanism of an Anole Lizard-Inspired Climbing Robot.

The stable operation of climbing robots exposed to high winds is of great significance for the health-monitoring of structures. This study proposes an anole lizard-like climbing robot inspired by its superior wind resistance. First, the stability mechanism of the anole lizard body in adhesion and desorption is investigated by developing adhesion and desorption models, respectively. Then, the hypothesis that the anole lizard improves its adhesion and stability performance through abdominal adjustment and trunk swing is tested by developing a simplified body model and kinematic model. After that, the structures of the toe, limb, and multi-stage flexible torso of the anole lizard-like climbing robot are designed. Subsequently, the aerodynamic behavior of the proposed robot under high-speed airflow are investigated using finite element analysis. The results show that when there is no obstacle, the climbing robot generates the normal force to enhance toepad friction and adhesion by tuning the abdomen’s shape to create an air pressure difference between the back and abdomen. When there is an obstacle, a component force is obtained through periodic oscillation of the spine and tail to resist the frontal winds resulting from the vortex paths generated by the airflow behind the obstacle. These results confirm that the proposed hypothesis is correct. Finally, the adhesion and wind resistance performance of the anole lizard-like climbing robot is tested through the developed experimental platform. It is found that the adhesion force is equal to 50 N when the pre-pressure is 20 N. Further, it is shown that the normal pressure of the proposed robot can reach 76.6% of its weight in a high wind of 14 m/s.

Influence of AC corona discharge on the hydrophobicity of silicone rubber surface in high-speed airflow environment

Corona discharge is one of the key factors that lead to the hydrophobicity loss of silicone rubber insulators used on the roof of high-speed trains. Based on the artificial experimental wind-tunnel platform, influences of AC corona intensity and airflow velocity on the hydrophobicity distribution of the silicone rubber surface were studied. According to the corona discharge phenomena and measured discharge current, influences of airflow velocity and voltage on the characteristics of corona discharge in a high-speed airflow environment were discussed. Results reveal that the hydrophobicity distribution on the silicone rubber surface shifts along the airflow direction in the high-speed airflow environment when the voltage is relatively high. When ionization zone develops to the needle-plate gap, the discharge path is deflected to the direction of airflow, which is responsible for the change of the hydrophobicity distribution. It is notable that the deflection distance decreases with the increase of airflow velocity. This is attributed to the fact that the electrons with variable horizontal distance from the electron to the plate electrode center are subjected to different electric field forces, resulting in different influences of high-speed airflow on them. These results are of engineering and theoretical significance for insulators used in high-speed railways.

Investigation of Water Films Shed From an Airfoil in a High-Speed Flow

Abstract The breakup of liquid films in high-speed flows is found in many applications. These include prefilming air blast atomization found in fuel injectors and shedding of droplet off of airfoils. In this work, a test rig has been developed and applied to study the breakup of water films from the trailing edge of an NACA 0012 airfoil placed in a high-speed air flow. The results provided reflect a new detailed dataset focused on air velocities above 75 m/s. Computational fluid dynamic (CFD) simulations were used to guide the development of the rig and the associated boundary and inlet conditions. In this work, air velocities up to 175 m/s were used with water films between 0.4 cm2/s and 3.6 cm2/s. The water film was introduced onto one surface through a series of 0.5 mm holes separated by 1 mm at a location 35 mm downstream of the leading edge of the vane. High speed video was used to document the sheet breakup behavior from the edge of the airfoil. Image analysis was used to identify the breakup length of ligaments formed. Laser diffraction was used 50 mm downstream of the trailing edge of the vane to determine the droplet size distribution and associated representative average diameters generated. A series of test conditions were run between 50 m/s and 175 m/s using multilevel factorial designed experiments. The results obtained were subjected to analysis of variance to generate correlations for breakup length and droplet representative diameters as a function of the conditions studied. The analysis was conducted on dimensionless versions of the variables studied to help connect the results to the physics of the situation. For example, rather than using air velocity to correlate the behavior, the Weber number (based on gas phase density and velocity) was used owing to its historical ability to describe liquid breakup processes. The results obtained are compared with other studies in the literature, and good agreement was found for the conditions at which a comparison could be made. It is observed that, for the conditions studied, liquid film thickness has little effect on the resulting droplet sizes—especially for the higher air velocity cases studied. The results also illustrate the sensitivity to choice of the characteristic length, which is generally consisted of trailing edge geometry or boundary layer thickness. In contrast, liquid film does influence the ligament breakup length, although the time to break up is less affected. Overall, the correlations developed provide engineering tools to help estimate ligament and drop size behavior for water films shed from airfoils in a high-speed flow.