Surrounding Air Flow Research Articles

Averaged Heat Fluxes Densities During Condensation and Evaporation of a Water Droplet

This study is intended for experimental investigation of the influence of boundary conditions on the intensity of phase transformations and heat transfer processes in a suspended water droplet. The results of the dynamics of the averaged heat fluxes densities during the droplet phase change cycle are presented and analysed. The influence of the droplet initial temperature, the surrounding air flow temperature and the additional humidity in the air flow were defined in separate regimes of the droplet phase transformations cycle. The experiments performed demonstrated that the parameters of the air flow surrounding the suspended water droplet affect the intensity of heat fluxes in the droplet throughout whole its phase change cycle. It was experimentally claimed that the initial temperature of the water droplet has no influence on the droplet heat and mass transfer processes in the equilibrium evaporation regime. The obtained results showed that most intensity heat flux densities are at the beginning of the droplet phase change cycle when condensation process occurs on the droplet’s surface in case with biggest amount of additional humidity in the surrounding air flow. This is very important in technologies of cleaning and heat recovery from flue gases.

Optimization of Co-Flow Jet Parameters for Ahmed Body Application

This study evaluates the drag reduction strategy of suction and blowing on idealize automotive vehicle, Ahmed Body. Optimization approach is adapted in order to analyse the effect of slot location, momentum coefficient and slot angle on the vehicle which experiencing drag. Despite all the efforts that have been done to reduce the Ahmed body drag using various active flow control system, most of the drag reduction were only less than 15%. A 25° Ahmed body with build in co-flow jet is modelled using a CAD software. The flow around the Ahmed body is simulated at Reynolds number based on length Re = 4.29 × 106. The governing equation were solve using an open source software package, which has been validated against experimental data. Pressure Implicit with Splitting of Operator (PISO) algorithm is applied to solve the equation. The outcome of the simulation are varies depending on the variables. Some show a decrease in drag while there are also that actually increase the drag of the system. This are caused by the suction and blowing slots that effect the surrounding air flow whether it is reducing or increasing the wake size downstream of the body. The result shows the momentum coefficient and location of both suction and blowing jet played an important role of manipulating the flow around the body and reducing the drag. The velocity contours indicated that the key to drag reduction is by using 40 m/s jet velocity, placement of suction and blowing away from each other.

The Research of the Fluid Dynamics of Trains

Trains have been the main means of transportation in the world for a long time. Therefore, the progress and design of trains has been a widely debated topic, and how to reduce the wear and tear of trains is a major aspect. There are many factors that can affect the resistance of a train as it moves. Including but not limited to Locomotive shape, the smoothness of the connections between the carriages of a train, the wheel axle and the adsorption device under the train and the train’s relative velocity with respect to air. This paper will study two main aspects of train fluid resistance. The first is the locomotive shape, that is, the effect of differences in the external shape of the train on the surrounding fluid. The other is the speed of the train, which is the influence of the relative speed of the train and the surrounding air flow on the surrounding fluid.

Investigation on Cooling Rate of Different Fin Design of an I.C. Engine by use of CFD

The Cylinder block is most important components in IC engine vehicles, which is under very high temperature stresses. To control the engine in efficient way we required to cool the cylinder, extended surface is provided on the cylinder to increase the speed of temperature reducing. By doing thermal analysis on the cylinder block fins, it is helpful to find the heat transfer outside the cylinder. The principle use in this research is to improve the heat dissipation rate by using the surrounding air flow direction and new geometry. We all know that, by expanding the surface area we can improve the heat transfer rate, so designing fin geometry. The main aim of using these cooling fins is to cool the engine cylinder by environmental air. The main aim of the research is to analyze the thermal properties by varying geometry, material and thickness of cylinder fins. Model is created to analyze and simulation purpose in solid works software. The models are created by varying the geometry and shape of fin. Present thickness and shape of the fin is changed. The 3D modelling software used is Solid works. In the current year Material used for manufacturing cylinder block’s fin body is Aluminium Alloy 204 it has thermal conductivity of 110-150W/mk. In this research, it is replaced with aluminium alloy 6061 and analysis is done in Ansys.

Analysis of Flow Characteristics of Different Shape Particles Chasing

in order to study the gas flow characteristics of particles with different shapes in the pursuit process, spherical, ellipsoidal and square particles are selected for numerical simulation by fluent. The results show that when the pursuit speed is the same, the streamline produced by square particles in the pursuit process is denser than that of spherical and ellipsoidal particles. Particle movement creates a certain vacuum on both sides and rear of the particle, causing the surrounding air flow to enter the areas on both sides of the particle, resulting in strong turbulence. After the rear particles catch up with the front particles, the changes of the surrounding flow field and streamline are similar to the inverse process before catching up, indicating that the particle motion has a certain regularity, and the square particles have the largest turbulent kinetic energy among the three particles.

Milling surface roughness for 7050 aluminum alloy cavity influenced by nozzle position of nanofluid minimum quantity lubrication

In nanofluid minimum quantity lubrication (NMQL) milling of aviation aluminum alloy, it is the bottleneck problem to adjust the position parameters (target distance, incidence angle, and elevation angle) of the nozzle to improve the surface roughness of milling, which has large and uncontrollable errors. In this paper, the influence law of milling cutter speed, helical angle, and cavity shape on the flow field around the milling cutter was studied, and the optimal nozzle profile parameters were obtained. Using 7050 aluminum alloy as the workpiece material, the milling experiment of the NMQL cavity was conducted by utilizing cottonseed oil-based Al2O3 nanofluid. Results show that the high velocity of the surrounding air flow field and the strong gas barrier could be attributed to high rotating velocities of the milling cutter. The incidence angle of the nozzle was consistent with the helical angle of the milling cutter, the target distance was appropriate at 25–30 mm, and the elevation angle was suitable at 60°–65°. The range and variance analyses of the signal-to-noise ratio of milling force and roughness were performed, and the chip morphology was observed and analyzed. The results show that the optimal combination of nozzle position parameters was the target distance of 30 mm, the incidence angle of 35°, and the elevation angle of 60°. Among these parameters, target distance had the largest impact on cutting performance with a contribution rate of more than 55%, followed by incidence angle and elevation contribution rate. Analysis by orthogonal experiment revealed that the nozzle position parameters were appropriate, and Ra (0.087 μm) was reduced by 30.4% from the maximum value (0.125 μm). Moreover, Rsm (0.05 mm) was minimum, which was 36% lower than that of the seventh group (Rsm = 0.078 mm).

Numerical study on the application of vacuum insulation panels and a latent heat storage for refrigerated vehicles with a large Eddy lattice Boltzmann method

The development of sustainable trucks has drawn a lot of attention lately. However, the reduction of fuel consumption and emissions related to deep frozen food transports has not yet been satisfactorily considered. In this paper, a thermal Large Eddy Lattice Boltzmann Method (LES-LBM) is applied to investigate two concepts for optimized refrigerated vehicles: (a) the inclusion of vacuum insulation panels (VIP) in the refrigerated body’s walls and (b) the introduction of a latent heat storage (LHS) to exchange fuel-driven air conditioning (AC), both with conveniently worth while potential to decrease fuel consumption and related emissions. The present numerical method allows for an accurate and efficient transient conjugate heat transfer simulation including the spatial and temporal resolution of the temperature distribution inside the insulation walls and the cargo in addition to the turbulent surrounding air flow induced by the AC. The present concept of VIP inclusion is found capable of halving the required cooling energy. In addition, it effectively reduces the variations in the temperature of the chilled goods during cooling operation, which is an important measure of the quality of the refrigerated body. The reduced required cooling energy is further found to enable the AC system to be replaced by a LHS mounted near the top of the refrigerator body and an additional ventilation system of lower total capacity. A comparison between simulations with conventional AC and LHS is conducted concerning the temperature homogeneity of loaded deep frozen food products. It is shown that a slight flow around the refrigerated goods is necessary and the maximum downtime of the AC system is 8 min in case of combined PUR and VIP insulation and 11 min in case of an additional LHS.

Reliable and Flow Independent Hydrogen Sensor Based on Microwave-Assisted ZnO Nanospheres: Improved Sensing Performance Under UV Light at Room Temperature

Miniaturized high-performance hydrogen (H2) sensors often suffer from reliability issues in terms of baseline drift and surrounding air flow. Normally, the sensors are often realized on microheaters to facilitate the redox reaction (desorption of generated water molecules at high temperature) to avoid the baseline drift, which leads to structural instability. In this paper, we report an UV (λ -400 nm/P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> -400 μW/P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</sub> -18 mW) excited ZnO nanosphere-based H2 sensor, which is almost independent of surrounding air flow with minimum base line drift. The ZnO nanospheres are synthesized by microwave-assisted technique and characterized at a different temperatures in the presence and absence of UV light to optimize the operating condition. It can be observed that the UV irradiated sensor is getting sufficient activation energy to enable the current modulation at different temperatures (60 °C and 100 °C), including room temperature (27 °C) in different concentrations of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (1% to 4%). By exploiting the UV radiation, flow independent (250-1000 sccm) with negligible baseline drift H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensor is demonstrated with fast response/recovery time at room temperature (27 °C). Theoretical reasoning for sensing characteristic is attempted to explain with the help of scanning electron microscopy, X-ray diffraction, ultraviolet-visible-near infrared, and photoluminescence spectrum. Flow dependence, repeatability, cross selectivity, and humidity tests were also conducted to study the reliable issues.

マイクロガスタービン圧縮機環境下の一様流中における水滴の蒸発効果

A model has been developed to investigate the evaporation behavior of water droplets in a uniform duct flow under gas turbine environments. It is assumed that the change of water droplet temperature is caused by convective heat transfer through droplet surface. The temperature of a water droplet has been calculated by treating the droplet as a lumped mass with a representative temperature uniformly distributed in the droplet. The proposed model consists of two steps. The 1st step is the heat transfer calculation between a water droplet and surrounding air flow and the 2nd step is the calculation to take the latent heat of vaporization into consideration. The evaporation rate is calculated based upon mass transfer between water droplet and surrounding air flow.

Mixture preparation and combustion in a GDI engine under stoichiometric or lean charge: an experimental and numerical study on an optically accessible engine

In direct injection spark ignition (SI) engines, the spray dynamics and interaction with the surrounding air flow are recognised as strongly affecting mixture quality, combustion development and amount of pollutants released at the exhaust. Spray impact against walls has also to be considered since undesired deposition of liquid as wallfilm causes unburned hydrocarbons and soot formation, hence increased fuel consumption and even augmented cyclic dispersion.Present work aims at clarifying the dynamics of sprays generated by multi-hole high pressure injectors in the combustion chamber of a gasoline direct injection (GDI) engine, as well as to characterize the combustion development and pollutants formation under various injection modes. Stoichiometric and lean operations are both studied into detail through a combined experimental and numerical approach. Experiments are conducted on an optically accessible engine, whereas numerical simulations are made after the development and validation of a three-dimensional (3D) sub-model reproducing at the best the spray dynamics also in its impact over walls.Early injection is shown to anyway determine at spark timing slight inhomogeneity in the equivalence ratio distribution of the stoichiometric charge, which makes for the flame propagation being anyway not spherical, but such to exhibit a preferential direction towards the richest zone of the combustion chamber. This leads to the formation of a pocket in the end gases where the knocking phenomenon is likely to occur under some circumstances. Lean charge operation is instead discussed as injection pressure and spark timing are varied to highlight mechanisms of formation of the main pollutants and to define routes for the development of proper engine control strategies. A deep insight in the in-cylinder thermo-fluidynamic processes is achieved thanks to the here followed synergic experimental-numerical approach.

Combined effervescent and airblast atomization of a liquid jet

Effervescent atomization shows great promise towards the production of small droplet sizes, but it can suffer from substantial instabilities. Adding a coaxial shear flow to a central two-phase bubbly flow is a simple extension of effervescent atomization, however, the characteristics of a combined air-blasting shear flow and effervescent mode of fragmentation have not been well described in the literature. By making use of LDA/PDA measurements, high speed microscopic imaging of the atomization zone, and advanced image processing techniques, quantities such as the axial velocity fluctuations, pulsation frequencies, ligament sizes and liquid area fractions are measured and analysed with respect to the relative mass of effervescent air and air-blast air. The work shows that the coaxial air blast flow does not change the frequency of the effervescent core pulsations but can act to dampen fluctuations whilst simultaneously improving dispersion characteristics. For this hybrid atomization mechanism, the measured axial velocity fluctuations are now a combined result of the instability of the effervescent spray core as well as mixing from the surrounding air flow. Analysis suggests that frequencies associated with the effervescent atomization process can occur on similar scales as the surrounding mixing frequencies. Furthermore, sinusoidal instabilities from the coaxial air flow are seen as superimposed onto the effervescent core indicating that a complex coupling can occur between the two modes of atomization.

Why a jetliner vibrates during takeoff: simulating air oscillations under the wing

Using a gas flow simulation tool, the oscillations of the air around the wing are analysed. It is pointed out that the flow behind and below the wing oscillates with sub- or low acoustic frequencies. Such external excitation may enter into resonance with the natural vibration frequencies of the wings and fuselage, which can produce a dangerous effect. The point of the article is that the fuselage vibration on takeoff depends mainly on what happens in the surrounding air flow. The tool used in flow simulation is equipped with the frequency analysis procedure that shows the spectrum of the oscillations (pressure) in selected points. This permits to identify the main frequencies and amplitudes of the oscillation. The results show that there are several sub-acoustic frequencies (infrasound) that may produce oscillating forces of up to several hundreds of kilograms per square meter of the wing. The topic is closely related to the safety issues.

ガスタービン圧縮機環境下の一様流中における水滴の蒸発効果

A model has been developed to investigate the evaporation effect of water droplets in a uniform duct flow under gas turbine compressor environments. The temperature of a water droplet has been calculated by treating the droplet as a lumped mass with a representative temperature uniformly distributed in the droplet. The proposed model consists of two steps. The 1st step is the heat transfer calculation between a water droplet and surrounding air flow and the 2nd step is the calculation to take the latent heat of vaporization into consideration.

Why a jetliner vibrates during takeoff: simulating air oscillations under the wing

Using a gas flow simulation tool, the oscillations of the air around the wing are analysed. It is pointed out that the flow behind and below the wing oscillates with sub- or low acoustic frequencies. Such external excitation may enter into resonance with the natural vibration frequencies of the wings and fuselage, which can produce a dangerous effect. The point of the article is that the fuselage vibration on takeoff depends mainly on what happens in the surrounding air flow. The tool used in flow simulation is equipped with the frequency analysis procedure that shows the spectrum of the oscillations (pressure) in selected points. This permits to identify the main frequencies and amplitudes of the oscillation. The results show that there are several sub-acoustic frequencies (infrasound) that may produce oscillating forces of up to several hundreds of kilograms per square meter of the wing. The topic is closely related to the safety issues.

A computational fluid dynamics study of the effects of buoyancy on air flow surrounding a building

In designing a durable building envelope, the air flow around a building plays an important role. Buoyancy is one of the factors that can affect air flow patterns. The contribution of outdoor buoyancy to the air flow surrounding a building was studied in this research. The building studied was the headquarters of the Malaysian Energy Commission. This building has a unique architectural outlook, and is called the Diamond Building due to its design. Outdoor field data such as air velocity, ambient temperature and surface temperature were collected during physical measurement. Air flow simulation was then carried out using the computational fluid dynamics software ANSYS. A total of four cases were studied in this research. Qualitative and quantitative analyses of the simulation results were carried out to show the influence of the outdoor buoyancy effect on the air flow patterns. The results showed that the air flow surrounding a building had a maximum velocity of 0.69 m/s dominated by the buoyancy effect when no wind was present. If a stronger natural wind of 3 m/s was present, the buoyancy effect was negligible. Practical application: The new findings from the outdoor buoyancy to the air flow surrounding a building in the tropics could be used as an important guide for building design engineers and researchers. The intention is to improve the design of building envelopes. Surrounding air flow has a significant influence on the building’s ventilation as well as the outdoor contaminant movement, and it penetrates the building’s envelopes. Surrounding airflow, which was considered solely contributed by wind previously, can now be examined at a more accurate airflow pattern by considering the buoyancy effect on airflow.

Improving aerodynamic performance of tall buildings using Fluid based Aerodynamic Modification

A novel approach is proposed to integrate active air flow control into the assembly of building envelopes in order to affect the interaction between tall buildings and surrounding air flow. The potential benefits of the proposed approach include reduction of embodied energy contained within the building structure, improvement of the overall life-cycle of building materials, and increased access to natural daylight by shallow lease spans. To date, the trend towards light-weight and high-strength materials in tall buildings, compounded with the emerging inclination towards modular prefabrication of structural assemblies, increasing flexibility and reduced damping, and greater slenderness ratios, has increased the susceptibility of the structural performance of tall buildings to dynamic wind load effects. Currently, mitigating wind loads relies on either changing structural or geometric characteristics such as the building׳s shape or through the addition of auxiliary damping systems. Furthermore, market driven pressures on increasing the slenderness ratios of tall buildings have been at odds with the socio-economic viability of the corresponding deep lease spans that tall buildings have required at their base. The proposed Fluid-based Aerodynamic Modification (FAM) approach is fundamentally different: instead of re-shaping the solid material to improve the aerodynamic ‘shape’ of the structure, fluid-based active flow control is used to manipulate the separating boundary layer in order to improve the building׳s aerodynamic performance and thus reduce the wind excitation.

Velocity-information-based force-term estimation of dielectric-barrier discharge plasma actuators

Particle image velocimetry measurements in close proximity to dielectric-barrier discharge plasma actuators are conducted to quantify the momentum transfer of the plasma to the surrounding air flow. Based on these data a comparative analysis of six existing approaches to estimate the induced body force is presented. Integral methods calculate an integral value for the actuator force based on the momentum-balance equation. Insight into the spatial distribution of the body force is provided by differential methods, which are based either on the Navier–Stokes equations or on the vorticity equation. It is demonstrated that the intensity as well as the domain of the force increase with increasing operating power levels. Emphasis is also placed on the issue of self-induced drag. It is shown that 30% of the induced momentum is consumed by wall friction. All results are validated with previously obtained balance force data and luminosity analysis of identical actuators.

Exposure assessment and engineering control strategies for airborne nanoparticles: an application to emissions from nanocomposite compounding processes

In this study, nanoalumina and nanoclay particles were compounded separately with ethylene vinyl acetate (EVA) polymer to produce nanocomposites using a twin-screw extruder to investigate exposure and effective controls. Nanoparticle exposures from compounding processes were elevated under some circumstances and were affected by many factors including inadequate ventilation, surrounding air flow, feeder type, feeding method, and nanoparticle type. Engineering controls such as improved ventilation and enclosure of releasing sources were applied to the process equipment to evaluate the effectiveness of control. The nanoparticle loading device was modified by installing a ventilated enclosure surrounding the loading chamber. Exposures were studied using designed controls for comparison which include three scenarios: (1) no isolation; (2) enclosed sources; and (3) enclosed sources and improved ventilation. Particle number concentrations for diameters from 5 to 20,000 nm measured by the Fast Mobility Particle Sizer and aerodynamic particle sizer were studied. Aerosol particles were sampled on transmission electron microscope grids to characterize particle composition and morphology. Measurements and samples were taken at the near- and far-field areas relative to releasing sources. Airborne particle concentrations were reduced significantly when using the feeder enclosure, and the concentrations were below the baseline when two sources were enclosed, and the ventilation was improved when using either nanoalumina or nanoclay as fillers.

Bed-inventory overturn mechanism for pant-leg circulating fluidized bed boilers

A numerical model was established to investigate the lateral mass transfer as well as the mechanism of bed-inventory overturn inside a pant-leg circulating fluidized bed (CFB), which is of great importance to maintain safe and efficient operation of the CFB. Results show that the solid loading along the central line of the pant-leg CFB is promotional to the lateral mass transfer across the central line as well as the bed-inventory overturn. Although the lateral pressure difference generated from lateral mass transfer inhibits continuing lateral mass transfer, providing the pant-leg CFB with self-balancing ability to some extent, the primary flow rate change due to the outlet pressure change often disable the self-balancing ability by continually enhancing the flow rate difference. As the flow rate of the primary air fan is more sensitive to its outlet pressure, it is easier to lead to bed inventory overturn. While when the solid particle is easier to follow the surrounding air flow, the self-balancing ability can be more active.

Solvability of reduced Possio integral equation in theoretical aeroelasticity

This paper is concerned with the solvability of the reduced version of the Possio singular integral equation, which plays a fundamental role in theoretical aeroelasticity. This equation relates the pressure distribution over a typical section of a long slender wing in subsonic compressible air flow to the normal velocity of the points of a wing (down-wash). In spite of the importance of the Possio equation, the question of the existence of its solution has not yet been settled. In this paper, we provide a rigorous study of the reduced version of the Possio equation and prove its solvability. The reduced Possio equation is important in its own right for two reasons: (a) it can be used as an approximate equation for the numerical analysis of the coupled system describing a vibrating wing in a surrounding air flow; (b) its analysis is essential for identifying analytical difficulties associated with the general Possio equation.