Aerodynamic Resistance Coefficient Research Articles

Seasonal and long-term dynamics in forest microclimate effects: global pattern and mechanism

Although the biophysical effects of afforestation or deforestation on local climate are recognized, the biophysical consequences of seasonal and long-term dynamics in forests on understory microclimate, which creates microrefugia for forest organisms under global warming, remain less well understood. To fill this research gap, we combined a three-layered (i.e., canopy, forest air space and understory soil) land surface energy balance model and Intrinsic Biophysical Mechanism Model and quantify seasonal (warm minus cool seasons) and long-term changes (later minus former periods) in the biophysical effects of forest dynamics on understory air temperature (ΔTa) and soil surface temperature (ΔTs). We found that high latitudes forests show strongest negative seasonal variations in both ΔTa and ΔTs, followed by moderate latitudes forests. In contrast, low latitudes forests exhibit positive seasonal variations in ΔTa and weak negative seasonal variations in ΔTs. For the long-term variations, ΔTs increases systematically at all three latitudes. However, the situation differs greatly for ΔTs, with a weak increase at low and moderate latitudes, but a slight decrease at high latitudes. Overall, changes in sensible and latent heat fluxes induced by forest dynamics (such as leaf area index), by altering the aerodynamic resistances of canopy and soil surface layers, are the main factors driving changes in forest microclimate effects. In addition, this study also develops an aerodynamic resistance coefficient {f}_{{rm{r}}}^{1} to combine the air temperature effects and surface soil temperature effects and proposes an indicator – ΔTSu, that is, Delta {T}_{{rm{Su}}}=Delta {T}_{{rm{s}}}+(frac{1}{{f}_{{rm{r}}}^{1}}-1)Delta {T}_{{rm{a}}}, as a possible benchmark for evaluating the total biophysical effects of forests on temperatures.

Study on the Dynamic Characteristics of Tensional Force for Ice Accumulated Overhead Lines Considering Instantaneous Wind Speed

Icing is one of the key factors affecting the security and reliability of power system operation. Ice accumulation on the overhead line (OHL) conductors is often accompanied by strong winds, whose magnitude and direction are varied constantly, which imposes challenges to the on-line monitoring of OHL’s ice load. This paper analyzed the dynamic characteristics of the tensional force for ice accumulated OHLs through both the on-site experiment and the finite element method (FEM). The correlation between the instantaneous wind speed, the thickness of the accumulated ice and the dynamic tensional force, the aerodynamic resistance coefficient of the conductor, is investigated. It is found that the axial dynamic tension at the end of the iced conductor is approximately proportional to the square of the instantaneous wind speed. The higher the wind speed, the larger the difference between the static tension and the maximum dynamic tension calculated using the 10-min average wind speed. Under the conditions of the example in this article (crescent-shaped icing), when the average wind speed is 20 m/s, the ratio of the difference to static tension is 11.19%. These conclusions are verified with the computational fluid dynamic (CFD) simulation, the same correlation is identified in comparison with the experiments. Due to the fact that the magnitudes of tensional force and vibration are determined by the instantaneous wind speed, significant error exists within traditional calculation methods where average wind speed is used instead.

Study of sports car aerodynamics using computer simulation methods

Problem. The results of the value of the coefficient of aerodynamic resistance of a sports car and the calculations of the frontal area of ​​its three-dimensional model are given. Goal. The goal is determination of the coefficient of aerodynamic resistance for a sports car by means of a computer experiment and justification of the feasibility of using attached parts to improve aerodynamics. Methodology. The method of computer experiment and three-dimensional modeling was used based on a comparison with the geometric and technical characteristics of a real car The results The accuracy of the construction of the three-dimensional model and virtual experiment was confirmed based on the obtained values of the frontal area and the coefficient of aerodynamic resistance.

Research on Drag Reduction of Heavy Truck Tail

In order to reduce the aerodynamic drag coefficient of a heavy van truck, three single-variable and one multi-variable composite drag reduction devices were designed based on the rear structure of the heavy van truck. The results show that among the three single-variable drag reduction devices, the inclination angle θ of the linear type drag reduction device has the greatest influence on the aerodynamic resistance coefficient of heavy vans truck, and the model has the best drag reduction effect when the inclination angle θ=20°, the aerodynamic drag coefficient is 0.7693, and the drag reduction rate is 7.64%. The radius R of the arc drag reducing device has the least influence on the aerodynamic drag coefficient. The multivariable composite drag reduction structure also has a good drag reduction effect. The study can provide a reference for the optimal design of the rear structure of related vehicles.

The effects of surface roughness on the aerodynamic drag coefficient of vehicles

In this study, the effects of surface roughness differences of vehicle coating materials (paint, paste, special applications, etc.) on the aerodynamic drag coefficient were inves-tigated using the finite element method. For this, aerodynamic drag forces and aerody-namic drag coefficients for speeds between 40-150 km/hours were calculated for a 1/20 scale vehicle designed by a package program by defining the body parts and front-rear window parts separately and assigning pre-calculated roughness values suitable in the industry, and the results were presented through graphs and visuals. Using three different paint roughness values (low, medium, and high), and one commonly used Teflon (fluoropolymer) coating, it was observed that the aerodynamic resistance coefficient in-creased with increasing roughness levels. Relative to the aerodynamic resistance coeffi-cient for the lowest paint roughness value, the aerodynamic resistance coefficient for the medium roughness value showed an increase of 0.000612529%, the aerodynamic resistance coefficient for the high roughness value showed an increase of 0.00104783%, and the aerodynamic resistance coefficient for the fluoropolymer coating showed an increase of 0.091195826%. In addition, the distribution of the pressure forces on the vehicle hood and windscreen were also observed in the study. It was observed that the pressure forces, which were approaching maximum on the front bumper, windscreen and side mirrors, were reduced over the rear windscreen area due to separated flow. It was also observed that the aerodynamic resistance force can be reduced by processes such as angular improvements to be made in the front bumper and vehicle windscreens.

The method of designing a disc-pad brake mechanism of the structural-parametric synthesis of the brake mechanism

A mathematical model of the method of designing a brake mechanism with a ventilated brake disc is developed based on the use of structural-parametric synthesis. The structural-parametric synthesis is performed according to two criteria: the temperature drop along the thickness of the brake disc and the coeffi cient of aerodynamic resistance to the friction of the air fl ow against the walls of the ventilation apparatus. Using these criteria and calculating the parameters of the brake mechanism, the design method allows you to choose the structure of the cooling unit and calculate its parameters. This method reduces the ranges of design and operational data of the cooling unit of the designed brake disc by means of optimization.

ОПТИМИЗАЦИЯ ПАРАМЕТРОВ ВЕНТИЛЯТОРНЫХ УСТАНОВОК АППАРАТОВ ВОЗДУШНОГО ОХЛАЖДЕНИЯ ГАЗА

Purpose of the study. Optimization of the parameters of high speed fan units of air coolers, the combination of which achieves the highest economic efficiency of fan units and, accordingly, the most rational range of specific speed values for the modes of maximum efficiency of fan units in combination with the relative diameter of the sleeve. Development of a mathematical model for determining the local values of the parameters of the efficiency of highspeed fan installations. Sustainable development of territories with active subsoil use is closely related to solving the problems of improving industrial safety and the efficiency of cooling the compressed gas at compressor stations of main gas pipelines, which actualizes the problem of mathematical modeling of energy conversion processes in the impellers of fan units of gas air coolers (AVO) to increase the competitiveness of the oil and gas complex RF in the context of globalization. Research methods. To optimize and determine the limiting combination of calculated parameters, the mathematical method of searching for the area of local maxima of a multiparameter problem in this part was performed in two stages: a mathematical model was built for determining the local values of the parameters that ensure the highest efficiency of fan installations with high speed; the most rational limiting combination of design parameters was determined, at which the highest economic efficiency of fan installations is achieved. Research results. The possibility of increasing the economic efficiency of axial fan units of high speed, made according to aerodynamic schemes with one impeller for gas air cooling devices, has been established. Using the mathematical analysis of the basic laws of axial turbomachines, equations for the efficiency of a fan unit and a fan are obtained, depending on the specific speed. Formulas are obtained for the maximum values of the efficiency of the fan and the fan unit of various specific speed depending on the coefficient of the consumpconsumption speed and on the relative diameter of the impeller sleeve. A method is proposed for constructing aerodynamic schemes of axial fan units for air-cooled gas coolers of the "K" type with maximum maximum values of efficiency for given values of specific speed, relative diameter of the impeller sleeve, aerodynamic quality of the impeller profiles, coefficient of aerodynamic resistance of the flow path of the coefficient of flow velocity. The possibility of creating a fan installation with a speed of ny ≥ 400 with an efficiency of at least ηy=0,86. Application area. Enterprises of the oil and gas complex of the Russian Federation for cooling compressed gas using AVO compressor stations of main gas pipelines.

Optimization of wind resistance in commercial vehicles with consideration of sunroof buffeting noise

The aim of this study was to reduce the aerodynamic resistance coefficient of heavy commercial vehicles and buffeting noise that occurs when a sunroof is opened. Computational fluid dynamics was used to establish a numerical simulation model of wind resistance and buffeting noise. Analysis shows that the main influences on aerodynamic resistance are the airflow impact on the roof dome and the wake vortex behind the cab. Sunroof buffeting noise is caused by a low-pressure turbulent vortex generated at the forehead of the cab and falls off at the sunroof. A strategy for reducing the wind resistance coefficient and sunroof buffeting noise is proposed, which involves optimizing the sun visor installation angle and roof dome shape. The optimal strategy is to increase the sun visor installation angle by 4° and use the Scheme 2 roof dome. After optimization, the aerodynamic resistance coefficient of the commercial vehicle was reduced by 2.07% and the sound pressure level of sunroof buffeting noise was reduced by 18.3 dB. Hence, the effect of optimization was obvious. This work provides guidance for reducing drag and buffeting noise in commercial vehicles.

To the problem of determination the aerodynamic resistance coefficient value to the swirled dust and gas flow in the air ducts of engineering and environmental systems

The experimental studies‘ results of the aerodynamic drag of a swirling dust and gas flow passing through a network of air ducts of engineering and environmental systems are presented. The limits of the method applicability for determining the aerodynamic resistance coefficient of a gas-dust swirling flow passing in a round aspiration duct, without taking into account the solid phase presence in it, have been determined.

Aerodynamic tests of small sized devices of recycled water-cooling

There is given a method of aerodynamic resistance coefficient determination of small-sized devices sprinklers of recycled water-cooling (mini cooling towers) in this article. Mini cooling towers are widely used at systems of recycled water supply in enterprises, because it are mobile, services a specific technological units or apparatuses, have a less energy intensity, more effective and safety unlike of oversized. There was compared two types of mini cooling towers in this labor: small-sized cooling tower with twisted air flow and with counter current flow. Also was developed and made the experimental unit for carry out of aerodynamic tests. The experiments on determination of aerodynamic resistance coefficient carried out depending on air flow rate in the interval from 0.5 to 3 m/s and irrigation density from 0 to 12 m3/(m2h). It shown that the sprinkler OB-65 (for mini cooling towers with twisted air flow, with diameter mesh casings 65mm) have more high aerodynamic resistance coefficient than the sprinkler OGGT-65 (for mini cooling towers with counter current flow with diameter mesh casings 65 mm) at the equal parameters of the experiment. Obtained coefficients of aerodynamic resistance of sprinklers in the mini cooling towers with the twisted air flow and with counter current flow approximated by the method of least squares and are presented as linear dependences in logarithmic coordinates of aerodynamic resistance and Reynolds number. It known that the coefficient of aerodynamic resistance is determine by common relation A/ReK.

Research of coefficient of aerodynamic resistance of a separation nozzle of industrial coolers

Water resources of Russia are a national wealth and not only the level of economic development of the country, but also health of the population depends on their state. Rational use of water resources at the industrial enterprises is provided with the independent, closed water supply systems equipped with devices of vaporizing cooling of water. The systems of reverse water supply are one of the most important elements of a technological complex of the enterprises of many industries: chemical, oil processing, petrochemical, machine-building, metallurgical, etc. Capacity of processing equipment, quality and cost of the product, a specific consumption of raw materials and the electric power depend on quality and overall performance of systems of reverse water supply. One of elements of a system of reverse water supply is the cooler. In this article the design of the water catcher of the cooler Application of the Offered Design is described will allow to reduce considerably moisture content in the steam-gas stream released by the cooler into the atmosphere.

Aerodynamic Properties of Tef for Separation from Chaff

The knowledge of the aerodynamic characteristics of tef grains and chaff (floating velocity, aerodynamic resistance coefficient) is significant for the construction and operation of machines, which treat substances with air flow and in all cases when substances are moved in the air. Terminal velocity and drag coefficient of tef grain and straw materials (Kuncho variety) have been experimentally measured by suspending the particles in an air stream. The effects of moisture content of tef grain, node position and length of straw on terminal velocity were studied. The results showed that moisture content have significant effects (p<0.01) on terminal velocity. By increasing moisture content from 7.3 to 25.94 % (w.b.), its terminal velocity increased linearly from 2.98 to 3.87 m/s. Drag coefficient of the tef grain decrease from 0.77 to 0.59 as moisture content increase from 7.3 to 25.94 %. The terminal velocity of the straws with different node positions (node free, end node, and middle node) and lengths (1 to 10 cm) were also measured. Keywords: Aerodynamic properties, terminal velocity, drag coefficient, tef, straw, node DOI : 10.7176/CER/11-3-05 Publication date : April 30 th 2019

Математичні моделі випаровування крапель в процесі руху в повітряному об’ємі приміщень

Математичні моделі випаровування крапель в процесі руху в повітряному об’ємі приміщень

Investigation of fuel consumption of a passenger car depending on aerodynamic resistance and related aspects: a case study

The research study investigates fuel consumption of a passenger car depending on aerodynamic resistance and related aspects. Introduction and next chapter describe all the resistance kinds affecting a passenger car while in-motion. Subsequent part outlines particular aspects such as aerodynamic resistance, aerodynamic resistance coefficient, car velocity and air temperature in terms of their effect on fuel consumption of selected passenger car. The most important chapter compares fuel consumption while a passenger car is in-motion on an expressway with closed and open windows with fuel consumption on a first class road infrastructure.

ИССЛЕДОВАНИЕ ЭЖЕКТИРУЮЩИХ СВОЙСТВ ПОТОКА ПОЛИФРАКЦИОННОГО СЫПУЧЕГО МАТЕРИАЛА

This work is aimed at confirming the adequacy of the probabilistic and statistical approach to determining the aerodynamic resistance coefficient of particles in a flow of the free falling polyfractional material, suggested by the author. The aerodynamic resistance coefficient of particles in a flow of falling material is defined by calculating the probability of finding particles out of air shadows of the neighboring particles. The laboratory experiment was performed on the offered experimental samples of bulk materials having different particle size distribution, but the identical average diameter of particles. The design of a laboratory experimental installation which allows determining the consumption of air, ejected by a polyfractional material flow, was described. The amount of the air, ejected with experimental samples, depends on their particle size distribution that confirms the insufficiency of describing the properties of bulk material only with the average diameter value. The given comparison of results of the analytical calculations with experimental data shows the reliability and adequacy of the calculated values.

New methodology for measuring the floating velocity of grain particles

The physical characteristics of particles used in agriculture (seeds, fertiliser particles) can strongly influence their movements in the agricultural machine as well as in the air. The knowledge of the physical characteristics of particles is essential for the designer and operators. In this respect the size, size distribution, shape, mass, bulk density, real density, coefficient of friction and aerodynamic resistance of particles are of great importance. Among physical characteristics, aerodynamic properties are the most important for the description of seed movement in the air.&#x0D; The knowledge of the aerodynamic characteristics of grains (floating velocity, aerodynamic resistance coefficient) is significant for the construction and operation of machines, which treat substances with air flow and in all cases when substances are moved in the air. The theory of the aerodynamic characteristics of regularly shaped bodies is well elaborated; however, grains (seed grains, fertilizer particles) applied in agricultural practice are irregularly shaped. Therefore, in our earlier research we started to study the physical characteristics of irregularly shaped grains. Due to their irregular shape, determining the size of grains is a troublesome process. A precise description of grains has to include several sizes (length, width, thickness) and can be obtained from the screen size of the corns.&#x0D; To identify the aerodynamic characteristics of seeds, we have developed a new elutriator, in which airflow is supplied by a centrifugal fan. The air velocity was measured with a thermal sensor. The collecting of data was supported by a digital camera, and we analysed the collected data by an image processing, so we can describe the movement of the seeds, and we can determine precisely the terminal velocity of irregular shaped seeds.&#x0D; The average moisture content of the samples was 13.42%. The individual mass of seeds varied between 0.1889 and 0.3758 g. The value of the mass of 1000 seeds used in general practice was 317.562 gr. The grain size varied: length between 7.76 and 11.81 mm, width between 6.77 and 9.99 mm, thickness between 4.41 and 5.85 mm. The suspension velocity varied between 9.14 m/s and 10.65 m/s.

Experimental Installation for Studying Hydroaerothermal Characteristics of Sprinklers and Water Traps of Cooling Towers

An experimental installation designed for engineering tests of sprinkling and water trapping devices is described. Aerodynamic tests were performed to determine the aerodynamic resistance coefficient of sprinklers and water traps and its dependence on the recirculating water and air flow rate. Hydroaerothermal tests were performed to determine the relative circulating water temperature based on a host of physical parameters. The experimental installation developed permitted measurements of the key process parameters with fair accuracy.

Airflow through net covered tunnel structures at high wind speeds

The airflow around and through net covered tunnel structures was experimentally and numerically analysed for wind speeds above 10 m s−1. A full scale tunnel structure covered with four different nets, characterised by different aerodynamic properties, was built. Wind speed was measured outside and inside the structure by means of two handheld rotary-cup anemometers. The same structure has been numerically analysed by two-dimensional Computational Fluid Dynamics (CFD) simulations where the net is modelled as a porous medium obeying the Forchheimer's law. Good agreement between full-scale and numerical results was observed. The numerical results were further validated against wind tunnel measurements of the aerodynamic pressure coefficients which are available in the literature. Both full scale experiments and numerical simulations indicate that the internal air velocity depends on the aerodynamic resistance coefficient of the net, rather than its solidity ratio.

An innovative experimental on-road testing method and its demonstration on a prototype vehicle

Ground vehicle drag coefficient is herein obtained using an unconventional on-road test in real scale. At low-Re numbers, and as a function of velocity variations, transition introduces changes on the vehicle’s drag coefficient. Therefore, the drag coefficient must be obtained as a function of velocity. Traditionally, only an average drag coefficient value is usually obtained using the coast down method. To obtain the on-road, velocity dependent, drag coefficients we introduce a new approach. The aerodynamic resistance coefficient is obtained by towing the vehicle with and without an aerodynamic shield, in order to eliminate the rolling resistance component. A detailed description of the method, its associated techniques, and related errors is presented. We conclude that the present experimental procedure is needed when comparing the experimental drag coefficient against computational results, since numerical computations are usually performed in a velocity dependent framework. Further, the same on-road test procedure is herein used to obtain the rolling and aerodynamic drag coefficient for a prototype vehicle working in the transition regime.

1862 空気の自然対流中での多孔板の流体抵抗係数の測定(J09-5 電子機器の放熱設計,J09 電子情報機器,電子デバイスの熱制御と強度・信頼性評価)

1862 空気の自然対流中での多孔板の流体抵抗係数の測定(J09-5 電子機器の放熱設計,J09 電子情報機器,電子デバイスの熱制御と強度・信頼性評価)