Interaction Of Airflow Research Articles

Characterization of the Aerodynamic Ground Effect and Its Influence in Multirotor Control

This paper analyzes the ground effect in multirotors, that is, the change in the thrust generated by the rotors when flying close to the ground due to the interaction of the rotor airflow with the ground surface. This effect is well known in single-rotor helicopters but has been assumed erroneously to be similar for multirotors in many cases in the literature. In this paper, the ground effect for multirotors is characterized with experimental tests in several cases and the partial ground effect, a situation in which one or some of the rotors of the multirotor (but not all) are under the ground effect, is also characterized. The influence of the different cases of ground effect in multirotor control is then studied with several control approaches in simulation and validated with experiments in a test bench and with outdoor flights.

Airflow mixing augmentation device for hot-air heating systems in modular boilers

The article demonstrates the results of the theoretical research devoted to the study of air flow interaction in hot-air heating systems of automatic modular boilers involving the use of fan heaters. The work quotes the results of mathematic simulation of various density air flows that are vertical to each other.

Potential energy savings achievable by zoned control of individual rooms in UK housing compared to standard central heating controls

Energy is wasted in domestic buildings when rooms that are heated are not occupied. Allowing those rooms to cool reduces the inside – outside temperature difference and therefore rate of heat loss, resulting in an energy saving. This suggests a cost effective way to upgrade an existing modern heating system, especially in older properties where other energy saving possibilities are limited. Assessing the savings achievable requires an analysis of a range of influencing factors, such as house type and age, location and occupancy patterns. Door opening has a major influence due to the impact on air exchange between heated and unheated zones in a house, so this was also considered.Annual simulations were carried out on dynamic models of the thermal and air flow interactions, for all combinations of influencing factors, to compare the potential energy savings of zoned versus non-zoned control.Savings of between 12% and 31% were obtained in the case of a semi-detached house model, and between 8% and 37% for a single storey bungalow. The largest percentage savings occurred in older properties, with interconnecting doors kept closed, and for the more intermittent types of occupancy. The average saving obtained for both house types was around 20%.

Experimental investigation of the interaction of supersonic airflow with transverse discharge

We have experimentally studied the interaction of a supersonic air flow with transverse electric gas discharge. Spectra of radiation emitted from various regions of the flow in the 600-700 nm wavelength range have been measured. Composition of the supersonic air flow is determined and peculiarities of its interaction with discharge have been studied. In particular, significant transfer of the electrode material with gas flow was observed.

Computational transport, phase change and deposition analysis of inhaled multicomponent droplet–vapor mixtures in an idealized human upper lung model

Numerous inhalable aerosols consist of multiple nano-to-microscale solid or liquid particles with dissolved or embedded compounds, as well as associated vapors. In general, of interest are the transport and conversion phenomena leading to local particle/droplet/vapor depositions. Selected examples include inhalation of aerosols from use of inhalers, cigarettes and electronic cigarettes. In this study the focus is on hygroscopic growth of nano-size multi-component droplets and droplet–vapor interactions during transport with subsequent deposition in a human upper lung-airway model. For that purpose a comprehensive and efficient computational fluid–particle dynamics model has been developed. It is capable of simultaneously analyzing multi-component droplet–vapor and airflow interactions with evaporation and condensation effects for different sets of inhalation conditions. Selecting inhaled electronic cigarette (EC) aerosols as an application, the simulation results include detailed transport, deposition and absorption data for different constituents (i.e., water, propylene glycol, glycerol and nicotine) in both vapor and liquid forms for an idealized human upper lung airway geometry, i.e., from mouth to generation 3. Results indicate that liquid–vapor phase change induces hygroscopic growth of droplets, which in turn impacts significantly the deposition concentrations of aerosols via inertial impaction, secondary flows, Brownian motion, and the vapor-specific absorption rates. Parametric sensitivity analyses were performed to evaluate the influence of different inhalation flow waveforms on EC-aerosol transport, interaction, and deposition.

공기흐름을 고려한 수리-역학적 연동모델에 의한 불포화 토사사면의 안정해석

Stability analysis based on the limit equilibrium method combined with the result of infiltration analysis is commonly used to evaluate the effect of rainfall infiltration on the slope stability. Soil is a three-phase mixture composed of solid particle, water and air. Therefore, a fully coupled mixture theories of stress-deformation behavior and the flow of water and air should be used to accurately analyze the process of rainfall infiltration through soil slope. The purpose of this study is to study the effect of interaction of air and water flow on the mechanical stability of slope. In this study, stability analyses based on the coupled hydro-mechanical model of three-phases were conducted for slope of weathered granite soil widespread in Korea. During the process of hydro-mechanical analysis strength reduction technique was applied to evaluate the effect of rainfall infiltration on the slope stability. The results showed an increase of air pressure during infiltration because rain water continuously displaced the air in the unsaturated zone. Such water-air interaction in the pore space of soil affects the stress-deformation behavior of slope. Therefore, the results from the three-phase model showed different behavior from the solid-water model that ignores the transport effect of air in the pores.

Regulating Effect of Asymmetrical Impeller on the Flow Distributions of Double-sided Centrifugal Compressor

AbstractTo achieve the rebalance of flow distributions of double-sided impellers, a method of improving the radius of rear impeller is presented in this paper. It is found that the flow distributions of front and rear impeller can be adjusted effectively by increasing the radius of rear impeller, thus improves the balance of flow distributions of front and rear impeller. Meanwhile, the working conversion mode process of double-sided centrifugal compressor is also changed. Further analysis shows that the flowrates of blade channels in front impeller are mainly influenced by the circumferential distributions of static pressure in the volute. But the flowrates of rear impeller blade channels are influenced by the outlet flow field of bent duct besides the effects of static pressure distributions in the volute. In the airflow interaction area downstream, the flowrate of blade channel is obviously smaller. By increasing the radius of rear impeller, the work capacity of rear impeller is enhanced, the working mode conversion process from parallel working mode of double-sided impeller to the single impeller working mode is delayed, and the stable working range of double-sided compressor is broadened.

Simulating Power Efficiency of Heat Transfer Agent Cooling Recirculation Systems at Power Plants

The article provides results of simulating processes of aerodynamic and heat-mass exchange interaction of air and water flows in evaporative cooling towers. It is found that use of the systems regulating direction and intensity of air flows cooling recirculating water of power plant turbine capacitors can be used commercially in order to enhance thermal efficiency and rise of electric power generation.

2상 흐름모델에 의한 강우침투를 고려한 불포화 토사 사면의 안정해석

Most previous studies on the rainfall infiltration and its influence on slope stability were based on the single-phase water flow model. The purpose of this study is to study the effect of interaction of air and water flow on the slope stability. In this study, two-phase flow analyses were conducted for weathered residual soil slopes with thin soil overlying impermeable bedrock. Results of the flow analysis were used as input for stability analysis by strength reduction method. Strength reduction method considers mechanical equilibrium to evaluate the effect of rainfall infiltration on the slope stability. The results show that remarkable delaying effects by air flow on the propagation of the wetting front and the deterioration of slope when surface ponding occurs during infiltration. On the other hand, the influence of the pore air flow on the slope stability can be neglected in the non-ponding situation with small rainfall intensity.

Numerical investigation on trimming of a single sail in a regatta

In sailing regattas, the actions of sailboats are to meet, overlap, pursue, pass, anti-collide, and defend. The aerodynamic performance of a sail based on a numerical simulation method is reported in this study. The parameters affecting the sail’s aerodynamic force coefficients, namely sailing angle, attack angle, mast shape, pitch angle, and camber ratio, are analyzed. From the results, basic principles and corresponding tactics of sail trimming are discussed and recommended for the start, during the windward, running, and leeward legs, before the finish, and near the marks. Sailors in the regatta should decrease the interaction of air flows around the sail to increase the lift force. The sailing angle, attack angle, pitch angle, and camber ratio should be adjusted to the appropriate degree to speed the boat when it is balanced. Sail trimming tactics have been practiced by professional sailors in regattas during which they can be scientifically supervised to compete against each other at Olympic Games.

Studying the interaction of supersonic air flow with transverse discharge

We have experimentally studied the interaction of a supersonic air flow with transverse electric gas discharge. Spectra of radiation emitted from various regions of the flow in the 600–700 nm wavelength range have been measured. Composition of the supersonic air flow is determined and peculiarities of its interaction with discharge have been studied. In particular, significant transfer of the electrode material with gas flow was observed.

Human body micro-environment: The benefits of controlling airflow interaction

This paper focuses on the micro-environment around a human body, and especially on its interaction with the surrounding environment. Research on the free convection flow generated by a human body (including the convective boundary layer around the body and the thermal plume above the body), its interaction with external invading flows and the resulting heat- and mass transfer, all of which are important for thermal comfort and inhaled air quality, is discussed. The benefit arising from control of the airflow interaction in the micro-environment, in terms of thermal comfort and inhaled air quality, is demonstrated by several methods that are applicable in practice.

Numerical Simulation of Hypersonic Flows

Numerical Simulation of Hypersonic Flows

Numerical Modeling for Discrete Multibody Interaction and Multifeild Coupling Dynamics Using the SPH Method

Discrete multibody interaction and contact problems and the multiphase interactions such as the sand particles airflow interactions by Aeolian sand transport in the desert are modeled by using the different kernel smoothing lengths in SPH method. Each particle defines a particular kernel smoothing length such as larger smoothing length which is used to calculate continuous homogenous body. Some special smoothing lengths are used to approximate interaction between the discrete particles or objects in contact problems and in different field coupling problem. By introducing the Single Particle Model (SPM) and the Multiparticle Model (MPM), the velocity exchanging phenomena are discussed by using different elastic modules. Some characteristics of the SPM and MPM are evaluated. The results show that the new SPH method can effectively solve different discrete multibody correct contact and multiphase mutual interference problems. Finally, the new SPH numerical computation and simulation process are verified.

Spray Distribution of Plain Orifice Atomizer in Preheated Air Flow

An experiment by taking photos of the spray field behind plain orifice atomizer was conducted to study its atomization in preheated air flow. The air flow condition was 0.14~0.2 Mach number and 300~400°C. Fuel-to-air momentum flux ratioQvaried from 0.4 to 9, and Weber numberWecovered the range of 60~140. Photos were analyzed by Matlab image processing toolbox. The results indicate that under the experiment conditions: (1) Under the same temperature, jet breakup length increases withQincreasing, and decreases with the increase ofWe. (2) As the air flow temperature increases from 300°C to 400°C, jet and air flow interaction affect the liquid column breakup more greatly than surface tension. (3) Under the same temperature, spray angle increases with the increase ofQ. (4) As the air flow temperature increases from 300°C to 400°C, evaporation affects the atomization more greatly than pneumatic nebulization.

Dynamic interaction of heat transfer, air flow and disc vibration of disc drives — Theoretical development and numerical analysis

Steady state air flow, heat transfer and thermoelastic dynamics in the multi-field coupling system of a rotating flexible disc in an enclosure filled with air are investigated within a large speed range. The system represents rotating discs in hard disc drives and optical disc drives. With Navier–Stokes and continuity equations and an improved penalty finite element method, air velocities and pressure induced by disc rotation in the enclosure are obtained. Temperature distribution of the rotating disc, driving shaft, enclosure and air flow is determined under the external heat sources from the shaft-driving motor and the circuit board inside the enclosure, the internal heat source from aerodynamic heating due to viscous dissipation of fluid, the heat convection in air flow, and the free convection heat loss at the enclosure׳s outside surfaces. Natural frequencies of the rotating disc are solved under the stresses induced by the disc temperature distribution and centrifugal force. Effects of heat convection and aerodynamic heating induced by disc rotation on system heat balance and dynamic characteristics of the rotating disc are investigated. The method presented is helpful to design of hard/optical disc drives and many other applications that involve rotating discs in fluids and with heat transfer.

Control-Oriented Gas Exchange Model for Diesel Engines Utilizing Variable Intake Valve Actuation

Modeling and control of the gas exchange process in modern diesel engines is critical for the promotion and control of advanced combustion strategies. However, most modeling efforts to date use complex stand-alone simulation packages that are not easily integrated into, or amenable for the synthesis of, engine control systems. Simpler control-oriented models have been developed; however, in many cases, they do not directly capture the complete dynamic interaction of air handling system components and flows in multicylinder diesel engines with variable geometry turbocharging (VGT), high pressure exhaust gas recirculation (EGR), and flexible intake valve actuation. Flexibility in the valvetrain directly impacts the gas exchange process not only through the effect on volumetric efficiency but also through the combustion process and resulting exhaust gas enthalpy utilized to drive the turbomachinery. This paper describes a low-order, five state model of the air handling system for a multicylinder variable geometry turbocharged diesel engine with cooled EGR and flexible intake valve actuation, validated against 286 steady state and 62 transient engine operating points. The model utilizes engine speed, engine fueling, EGR valve position, VGT nozzle position, and intake valve closing (IVC) time as inputs to the model. The model outputs include calculation of the engine flows as well as the exhaust temperature exiting the cylinders. The gas exchange model captures the dynamic effects of the not only the standard air handling actuators (EGR valve position and VGT position) but also IVC timing, exercised over their useful operating ranges. The model's capabilities are enabled through the use of analytical functions to describe the performance of the turbocharger, eliminating the need to use look-up maps; a physically based control-oriented exhaust gas enthalpy submodel and a physically based volumetric efficiency submodel.

Human convective boundary layer and its interaction with room ventilation flow.

This study investigates the interaction between the human convective boundary layer (CBL) and uniform airflow with different velocity and from different directions. Human body is resembled by a thermal manikin with complex body shape and surface temperature distribution as the skin temperature of an average person. Particle image velocimetry (PIV) and pseudocolor visualization (PCV) are applied to identify the flow around the manikin's body. The findings show that the direction and magnitude of the surrounding airflows considerably influence the airflow distribution around the human body. Downward flow with velocity of 0.175m/s does not influence the convective flow in the breathing zone, while flow at 0.30m/s collides with the CBL at the nose level reducing the peak velocity from 0.185 to 0.10m/s. Transverse horizontal flow disturbs the CBL at the breathing zone even at 0.175m/s. A sitting manikin exposed to airflow from below with velocity of 0.30 and 0.425m/s assisting the CBL reduces the peak velocity in the breathing zone and changes the flow pattern around the body, compared to the assisting flow of 0.175m/s or quiescent conditions. In this case, the airflow interaction is strongly affected by the presence of the chair.

Improved inhaled air quality at reduced ventilation rate by control of airflow interaction at the breathing zone with lobed jets

Inhaled air quality at a reduced supply of clean air was studied by controlling the airflow interaction at the breathing zone of a person using lobed jets as part of personalized ventilation (PV). Experiments were performed in a full-scale test room at 23°C (73.4°F) with a breathing thermal manikin seated at a workstation, with realistic free-convection flow around the body and a normal breathing cycle. The air in the room was mixed with tracer gas R134a. Clean air was supplied isothermally from three nozzles with circular, four-leafed clover, and six-edged star openings of 0.025 m (0.08 ft) equivalent diameter. The nozzles were positioned frontally at the face within the boundary layer and centered to the mouth. The enhancement of inhaled air quality by changing the initial velocity (0.2–0.6 m/s, 0.66–1.97 fps) and the distance from the mouth (0.02–0.06 m, 0.07–0.20 ft) was studied. The control over the interaction between the inserted jets and the free convection flow was efficient. Over 80% clean PV air was measured in inhalation. The worst performing nozzle was the four-leafed clover: its best performance yielded 23% clean air inhalation, at the shortest distance and the highest velocity. The other lobed nozzle, the six-edged star, performed similarly to the circular nozzle.

Investigation of Multiple Miniature Axial Fan Cooling Solutions and Thermal Modeling Approaches

This paper investigates the thermal and fluid dynamic characteristics due to multiple miniature axial fans with blade chord and span length scales less than 10 mm, impinging air onto finned surfaces. A coupled approach, utilizing both experimental and numerical techniques, has been devised to examine in detail the exit air flow interaction between cooling fans within an array. The findings demonstrate that fans positioned adjacently in an array can influence heat transfer performance both positively and negatively by up to 35% compared to an equivalent single fan—heat sink unit operating standalone. Numerical simulations have provided an insight into the flow fields generated by adjacent fans and also the air flow interaction with fixed fan motor support structures downstream. A novel experimental approach utilizing infrared thermography has been developed to locally assess the validity of the numerical models. In particular, an assessment on implementing compact lumped parameter fans and fans modeled with full geometric detail is shown for two configurations that are impinging air onto finned and flat surfaces. Overall, the study provides an insight into fan cooled heat sinks incorporating multiple miniature axial fans and general recommendations for improving current numerical modeling approaches.