High-speed Airflow Research Articles

Effects of airflow direction on the thermal-hydraulic performance of louvered fin-common flow up vortex generator

To improve the thermal-hydraulic performance of the louvered fin and flat tube heat exchangers (LFHEs), this paper innovatively proposes the louvered fin-common flow up vortex generator (LF-CFUVG). Then, numerical simulations are conducted to study the effects of airflow direction γ on the thermal-hydraulic performance of the LF-CFUVG. The corresponding results indicate that the flow resistance of the LF-CFUVG is always greater than the Baseline (the LFHE without CFUVGs), as the CFUVGs reduce the minimum free flow area while forming low-speed wake zones behind them. The heat transfer capacity of the LF-CFUVG exceeds the Baseline as well, this is attributed to the longitudinal vortices induced by the CFUVGs, which is helpful to homogenize the temperature field and transport the high-speed and low-temperature airflow. And the thermal-hydraulic performance of LF-CFUVG also outperforms the Baseline. In comparison to the working condition of γ is 0°, the pressure drop Δp for the LF-CFUVG declines with increase of γ from 0° to 30°, thus a larger angle helps to reduce flow resistance. However, the heat transfer coefficients hLF and performance evaluation criteria (PEC) of the LF-CFUVG deteriorate with the increasing γ, so a smaller angle is recommended to obtain an intenser heat transfer and better PEC.

Stall characteristics of wavy leading-edge airfoil in subsonic and transonic airflows

Based on the bioinspired wavy leading-edge, the stall characteristics of the NACA0012 airfoil are optimized. In this paper, the semicircle plus line segment is used to obtain the wavy leading edge. The aerodynamic forces of the airfoil are measured by a high-precision balance, and the detailed flow features of the airfoil are obtained by the oil flow tests. Then, combined with numerical simulation, the optimization mechanism is obtained. The operating conditions are as follows: Mach number ranging from 0.4 to 0.8, and angle of attack ranging from −4° to 25°. The results show that in high speed airflows, compared with the basic airfoil, the lift coefficient of the wavy leading-edge airfoil does not decrease sharply with the increase of the angle of attack, and the drag coefficient of the wavy leading-edge airfoil is similar to the basic airfoil; among the three types of airfoils studied, the larger wavy leading-edge feature size has better aerodynamic characteristics; combined with the numerical simulation results, it can be seen that the stall mechanism of airfoils varies at different Mach numbers. The wavy leading-edge generate streamwise vortex. The streamwise vortices increase energy transport in the boundary layer. Therefore, the separation zone moves toward the trailing edge of the airfoil, and the stall characteristics of the airfoil are optimized.

High-temperature transient-induced thermomechanical damage of fiber-reinforced ceramic-matrix composites in supersonic wind tunnel

This article is based on the supersonic directly connected wind tunnel. Through a specially designed experimental chamber, combined with infrared temperature measurement, high-speed camera, etc., in-situ monitoring of composite materials under airflow at Ma 3.0 with a total temperature of 950 ∼ 1473K was carried out. The dimensional analysis method was used to propose dimensionless parameters to characterize the thermal coupling caused by high-speed airflow thermal shock. Research has shown that the thermal coupling effect of supersonic airflow causes uneven temperature inside the material, and the thermal stress caused by temperature gradient changes (including increasing and decreasing processes) is the main reason for material damage. The damage of ceramic matrix composites under thermal shock mainly manifests as a decrease in surface roughness, surface fiber fracture and a decrease in elastic modulus. In addition, the study also found that there are damage thresholds for the thermal shock effect of airflow at different total temperatures, which helps to further understand the thermomechanical damage mechanism and degradation law of composite structure under high-temperature transient conditions.

TEMPERATURE FACTOR EFFECT ON PULSATING HYDROGEN COMBUSTION IN A HIGH-SPEED AIR FLOW

The results of a numerical study of the combustion of hydrogen jets injected into a highspeed air flow before a sudden channel expansion are presented. It is shown that under constant input conditions, a pulsating combustion mode is realized in the channel, which is maintained when the wall temperature increases from 300 to 900 K. An increase in the temperature factor leads to a decrease in the oscillation frequency and amplitude.

Numerical investigation on the characteristics of underbody aerodynamic noise sources in electric vehicles

As the wind noise caused by the upper body is gradually controlled, the influence of high-speed underbody airflow on the interior noise of electric vehicles becomes increasingly prominent. The method involves the combined application of the Finite Volume Method (FVM) and Finite Element Analysis (FEA) to compute the aerodynamic noise inside a real vehicle model induced by high-speed airflow. A numerical simulation of the underbody wind noise in electric vehicles has been conducted to reveal the noise sources at the bottom of electric vehicles and cabin noise. Finally, the impact of side skirts and wind deflectors on chassis wind noise was evaluated.

Study on multiple influence mechanism of airflow-dust-gas coupling diffusion under large vortex flow technology

In response to the serious dust pollution and excessive gas concentration in fully mechanized excavation face, a multi-phase coupling diffusion model of airflow-dust-gas was established, and the influence of pressure pumping ratio and air volume on dust and gas diffusion was studied. The results showed that the dust of the traditional ventilation mode was diffused to the whole roadway, and the high-concentration gas accumulated obviously. However, after adopting the new ventilation mode of large vortex flow, a quantity of dust was controlled in the eddy field, and high-concentration gas was dissipated by strong airflow, so there was no gas accumulation. As the pressure pumping ratio decreases, the extraction effect increases, the eddy current intensity also increases, and the control effect on dust is enhanced. The pressure pumping ratio with the best dust control effect is 0.6, and there is no dust pollution and no gas accumulation in the driver's location. The fixed pressure pumping ratio is 0.6, and the diffusion of dust and gas is not significantly affected by an increase in air volume, but high-speed airflow can dilute and reduce the concentration of dust and gas. When Qb = 600.0 mg/m³, the high-speed airflow can dilute the dust concentration, accelerate the dispersion of high-concentration gas, keep the gas below the safe level, and have a good dust control effect. The increase of air volume will further reduce the dust and gas concentration. This study provides a theoretical basis for the promotion and utilization of new ventilation method on-site.

Multiphysics modeling for local structural heat source and high-speed airflow coupled ablation behavior of the lightweight quartz fiber-reinforced phenolic (LQFRP) composite

Multiphysics modeling for local structural heat source and high-speed airflow coupled ablation behavior of the lightweight quartz fiber-reinforced phenolic (LQFRP) composite

Experimental study on spray characteristics of aviation kerosene from a pressure-swirl nozzle in high-speed airflow with elevated temperatures

Spray characteristics of aviation kerosene are critical to the performance of gas turbine combustors. Actual gas turbine combustors are mainly operated at high temperatures and high-speed airflow environments, whereas almost all research on spray characteristics in high-speed airflow is limited to room temperature in the literature. In this paper, the spray characteristics of aviation kerosene from a pressure-swirl nozzle are investigated experimentally in the airflow temperature range of 313–500 K and the airflow speed range of 108–136 m/s. The information on spray characteristics such as droplet flux, velocity, and diameter was obtained by phase Doppler anemometry. Planar Mie scatter was performed to obtain the information on the concentration distribution of spray. The results show that the droplet flux, velocity, concentration, and Sauter mean diameter (D32) change significantly with airflow temperatures. In special, D32 in the center recirculation zone shows an increasing trend with increasing airflow temperature. The difference in the change of D32 along the propagation direction at elevated airflow temperatures is mainly due to the difference in evaporation processes. It was found that the evaporation models of a droplet that existed in literature do not predict well the D32 variation of spray in this experiment. A new spray evaporation model considering turbulence and fuel vapor fraction is proposed, which significantly reduces the prediction errors of variation in D32 in this experiment. This paper can provide experimental data and preliminary theoretical references for subsequent investigation of spray characteristics in high-speed airflow with elevated temperatures.

Numerical study on the three-dimensional flow of water film on the outer surface of the hollow stationary blade

In order to figure out the influence of water film on the performance of the turbomachinery, understand the mechanism of the interaction between the high-speed airflow and the water film in turbomachinery, and provide a reference for the design of the subsequent experiments and hollow stationary blade water removal by heating. The commercial software FLUENT with the Eulerian Wall Films model is used to establish a solution method for simulating the flow of water film on the blade. The accuracy of the solution method is verified by comparing it with the results of the water film thickness experiment on the surface of the plate. The distribution of the water film on the outer surface of the vane as well as the influence of the water film on the mainstream field are numerically studied in the condition of the wet steam mainstream. The results show that the gradient of water film thickness on the pressure surface is relatively gentle and is along the radial direction. The gradient of water film thickness on the suction side is along the axial direction, and the value is larger; There is a V-shaped water film agglomeration area on the suction surface near the trailing edge where the water film thickness is greater than 45.7 μm; The top areas on both the suction side and pressure side produce a local water film agglomeration area with the dual effect of the secondary flow and the centrifugal force of the mainstream; The water film flow on the blade surface has little influence of the steam velocity and the speed of the mainstream. The increase of local pressure on the surface leads to an increase in the pressure of the adjacent mainstream areas.

Research on guided wave propagation characteristics of quartz ceramic thermal protection structure for ablation monitoring

ABSTRACT Monitoring the thermal protection structure (TPS) of hypersonic vehicles is vital for ensuring safe flight. The guided wave(GW) structure health monitoring（SHM）method is promising for TPS health monitoring due to its high sensitivity, ability to detect small damages, and wide monitoring coverage, both online and offline. However, there is currently a clear research gap in monitoring hypersonic aircraft TPS in real-service environments. This paper addresses this gap by conducting GW monitoring research on hypersonic vehicles TPS under simulated real-service conditions, involving high-temperature and high-speed airflow ablation. This study takes quartz ceramic TPS as the object, undertaking a preliminary investigation into its GW propagation characteristics. Subsequently, the TPS underwent high-temperature and high-speed oxygen-acetylene ablation at 2100°C to induce damages. GW monitoring was then conducted to capture GW signals in both undamaged and various damage scenarios. Through signal analysis, characteristic parameter extraction, and application of the damage index method, rules governing how GW signals respond to damage were established. Results indicate significant impacts on amplitude and phase of GW signals with increasing damage severity, validating the feasibility of the GW monitoring method for detecting high-temperature and high-speed airflow damage to TPS and supporting its expansion for damage monitoring.

Self-aspiration sampling design for rapid analyses of volatile organic compounds based on atmospheric pressure chemical ionization/photoionization combined ionization source mass spectrometry.

Development of combined mass spectrometry ionization sources has enabled expansion of the application and scope of mass spectrometry. A novel hybrid ionization system combining vacuum ultraviolet (VUV) and atmospheric pressure chemical ionization (APCI) was constructed. Gaseous samples were self-aspirated into an ionization zone through a capillary by negative pressure, generated by high-speed airflow based on the Venturi effect. Compared with APCI mode alone, the signal-to-noise ratio (S/N) in APCI/VUV mode was increased by about 276-times. To increase the ionization efficiency further, correlated experimental conditions were optimized. Four types of volatile organic compounds (VOCs) were tested to evaluate the performance of the APCI/VUV ion source. Excellent linearity and limit of detection were achieved for compounds in mixed solutions. Quantitative analyses of four VOCs (toluene, cyclohexanone, styrene and ethylbenzene) using APCI/VUV-MS were done, and the relative standard deviations (RSDs) were 1.57%, 6.30%, 4.49% and 8.21%, respectively, indicating that the APCI/VUV ionization source had excellent reproducibility. Our results demonstrated that the developed method was promising for analyzing VOCs as well as being rapid, simple, and easy to operate.

Numerical simulation of the fine kinetics of dust reduction using high-speed aerosols.

A numerical model of single-particle fog-dust collision coupling in a high-speed airflow based on three-phase flow theory. The effect of the fog-to-dust particle size ratio, relative velocity between the fog and dust particles, collision angle and contact angle at the wetting humidity function of dust particles is investigated. Different particle size ratios are determined for achieving the optimal wetting humidity for the interaction of high-velocity aerosols with dust particles of different sizes, for differ, that is, kPM2.5 = 2:1, kPM10 = 3.5:1 and kPM20 = 1.5:1. The optimal humidity increases with the relative velocity U between the fog and dust particles in the high-speed airflow. The larger the collision angle is, the lower the wetting rate is.The smaller the contact angle between the solid and liquid is, the better droplet wetting on dust is. The fine kinetic mechanism of single-particle fog-dust collision-coupling in a high-speed airflow is elucidated in this study.

Numerical Study of Low-Temperature Ventilation Drying in a Wheat Grain Silo Considering Non-Uniform Porosity Distribution

The temperature and moisture content inside a grain pile are two important indicators for judging the safety of grain storage. To accurately predict the temperature and moisture content inside a grain pile, a numerical simulation was carried out of the drying process of a mesoscale wheat grain soil based on a thin-layer drying method, considering non-uniform porosity. The effectiveness of this method for wheat piles was verified through a comparison with the experimental data. The influence of different ventilation cage heights and ventilation temperatures on heat and moisture transfer in the wheat grain pile were also studied. The results show the following points. The numerical simulation method in this paper can effectively predict the temperature and moisture content of a wheat grain pile. The non-uniform porosity distribution model can better reproduce the state of ventilation during storage of wheat grain piles than the uniform porosity distribution model. The distribution patterns of flow lines in silos with different ventilation cage heights have certain similarities, but the high-speed airflow area will decrease as the height of the ventilation cage increases. Different ventilation temperatures will significantly affect the areas of high temperature and the rewetting inside a wheat grain pile.

Experimental and numerical study on airflow-dust migration behavior in an underground cavern group construction for cleaner production

A large amount of dust will be generated during the construction of underground cavern group. The understanding of the dust migration in the construction ventilation of the underground cavern group can help to optimize the cavern group’s ventilation design and improve the ventilation scheme of the cavern group’s rationality. In this paper, the effects of dust particle size, dust migration path, initial dust concentration in cavern, tunnel entrance wind speed and air duct outlet wind speed on dust migration were studied by combining a model test and numerical calculation. The results show that in the process of dust ventilation migration, the larger the diameter of the dust particles, the more difficult it is to discharge. The time of dust concentration reducing to 2 mg/m3 has a logarithmic distribution with ventilation conditions. The high-speed airflow from the outlet of the air duct is an important factor affecting the migration of dust. The development of airflow is divided into vortex region, recirculation region, collision region and stability region. Vortex region and collision region have lower wind speed and higher dust concentration, which are the unfavorable positions in the ventilation process. In the actual construction process, shortening the distance of dust migration can make the dust discharge quickly. The amount of dust generated by construction has a significant impact on the peak concentration of dust migration. During the ventilation process, the wind speed at the entrance of the tunnel and at the outlet of the air duct has a significant impact on the migration time of dust, at the same time, the ventilation efficiency should be considered while selecting the wind speed.

Experimental Study on the Influence of Water Barrier Placement Position on Shock Wave Pressure Peak

According to the self-built experimental platform, the shock wave experiment with and without a water barrier was carried out, the influence of the existence of a water barrier on the shock wave pressure peak was compared, and the influence of the water placement position on the attenuation effect of the pressure peak was studied. The experimental results show that the existence of a water barrier can completely attenuate the shock wave over-pressure peak, but the formation of aerosol clouds driven by high-speed airflow after the water barrier wave will produce corresponding dynamic pressure peaks. The effect of attenuating the pressure peak will not be achieved near the water barrier, and the pressure peak can be effectively attenuated farther away from the water barrier.

Theoretical modeling and multi-parameter influence analysis of piston wind in the ultra-high-speed elevator hoistway

The high-speed airflow generated when an ultra-high-speed elevator runs in the hoistway will cause a significant piston effect. Therefore, it is essential to study the variation law of the piston wind in the hoistway and the influence of different parameters on the piston wind in the hoistway. This paper first establishes the theoretical model of the piston wind in the hoistway when the elevator ascends, descends, and intersects based on the unsteady flow theory of the Bernoulli principle. The effectiveness and accuracy of the theoretical model are verified through experimental measurements and numerical simulations. Second, based on the verified theoretical model, the influence of the five parameters of the car speed, car height, hoistway height, blockage ratio, and frictional resistance coefficient on the variation law of the piston wind and ventilation rate in the hoistway is systematically analyzed. Integrating the five parameters, a multi-parameter universal theoretical formula for hoistway ventilation rate is proposed. Finally, a gray correlation analysis is performed on each influencing parameter, which showed that the piston wind in the elevator hoistway is most affected by the blockage ratio, followed by the car speed, hoistway height, and frictional resistance coefficient, and is least affected by the car height.

Damage evolution simulation and laser ablation mechanisms of C/SiC composites under in high-speed airflow environment

Damage evolution simulation and laser ablation mechanisms of C/SiC composites under in high-speed airflow environment

Fiber Bragg Grating Total Temperature Probes for High-Speed Airflow With High Recovery Factor

Fiber Bragg Grating Total Temperature Probes for High-Speed Airflow With High Recovery Factor

An airflow-driven system for scalable production of nano-microfiber wrapped triboelectric yarns for wearable applications

Nanofibers, with their large aspect ratio, high specific surface area, and high porosity, hold great promise for applications in textile materials, biomedicine, and smart wearables. Currently, the primary method for producing nanofibers is electrospinning. However, this method carries operational risks due to the use of high-voltage electrostatic fields, and it is not suitable for large-scale production due to low efficiency. To address these challenges, we propose an air-driven spinning system that combines solution blow spinning and vortex tubes for the scalable production of polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) nano-microfiber wrapped conductive yarn. The airbrushing machine allows for high-speed production of PVDF-TrFE nano-microfibers through solution blow spinning, with a maximum production rate of approximately 36 ml/h. The vortex tubes apply rotation and twist to the core yarn using high-speed airflow to bond the nano-microfibers to core yarn. By optimizing the process, we achieve a tight integration between the outer layer of nano-microfibers and the inner layer of conductive core yarn, imparting water repellency, flexibility, washability, air permeability, and a certain level of abrasion resistance to the resulting yarn. We demonstrate the applications of this yarn as triboelectric nanogenerators, including energy harvesting and self-powered sensing. Furthermore, we employ this method to prepare stretchable self-generating triboelectric yarn. This air-driven spinning system overcomes the limitations of electrospinning, providing a scalable and efficient method for the production of nano-microfiber-wrapped yarns with various functional properties.

Investigation of water separation capabilities of demisters integrated with microstructured surfaces

Demisters with high water separation efficiencies play an important role in performance enhancement of thermal desalination. Bio-inspired, microstructured surfaces have been highlighted due to the potential to considerably increase water separation by enhancing water capturing and transporting features. However, experimental investigation on the performance enhancement of the demisters with those functional surfaces is still lacking. Herein, we demonstrate water collection and separation characteristics of the large-scale demisters integrated with hybrid microstructured surfaces. Particularly, the hybrid microstructured polypropylene surfaces to possess the vertically-aligned spiky cone arrays along with multiple sets of open-type microchannels are successfully fabricated in uniform manner by using an injection molding process. The fabricated hybrid microstructured surfaces perform twice and up to 3.2 times higher water collection than the control planar surfaces in low-speed and high-speed air flows, respectively, owing to their enhanced water capturing and transporting capabilities by the capillary pressure generated by the microstructures. As a model study, the inner surfaces of the axial cyclone-type demister ducts are modified with the hybrid microstructured surfaces, leading to up to 12 % enhancement of the water separation efficiencies of the demisters, compared to the control planar surface demister in high-speed air flow.