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EN
Motor coolers are operated with the coupling of temperature and pressure fields, in which the change rule is affected by multiple factors. In this study, the thermal resistance of the motorcooler was examined using the velocity coefficient method to reveal the influence of heat transfer and wind resistance. The temperature and pressure fields were analyzed using the finite element method based on the hydrodynamics and momentum theorem. By varying the heat transfer and wind resistance coefficients to reflect temperature and pressure characteristics, wind and water velocities were determined. Results demonstrate that the total convective heat transfer and wind resistance coefficients of the cooler model are sensitive to variations in face-to-face wind velocity, but not to those of the cooling water flow rate. When wind velocity increases from 0.8 to 5.19m/s, the total convective heat transfer increases by 1.85 times and wind resistance increases by 18.74 times. Variations in cooling water velocity has little effect on the Nusselt numberon the air side and the Euler number of the single row tube, which are multiplied with the increase of the Reynolds number. When the Reynolds number increases from 1020 to 6345, the Nusselt number increases by 2.05 times and the Euler numer decreases by 2.29 times. The results provide references for the design and performance testing of high-power motor coolers.
EN
This article presents a two-dimensional steady viscous flow simulation past circular and square cylinders at low Reynolds numbers (based on the diameter) by the finite volume method with a non-orthogonal body-fitted grid. Diffusive fluxes are discretized using central differencing scheme, and for convective fluxes upwind and central differencing schemes are blended using a ‘deferred correction’ approach. A simplified pressure correction equation is derived, and proper under-relaxation factors are used so that computational cost is reduced without adversely affecting the convergence rate. The governing equations are expressed in Cartesian velocity components and solution is carried out using the SIMPLE algorithm for collocated arrangement of variables. The mesh yielding grid-independent solution is then utilized to study, for the very first time, the effect of the Reynolds number on the separation bubble length, separation angle, and drag coefficients for both circular and square cylinders. Finally, functional relationships between the computed quantities and Reynolds number (Re) are proposed up to Re = 40. It is found that circular cylinder separation commences between Re= 6.5-6.6, and the bubble length, separation angle, total drag vary as Re, Re-0.5, Re-0.5 respectively. Extrapolated results obtained from the empirical relations for the circular cylinder show an excellent agreement with established data from the literature. For a square cylinder, the bubble length and total drag are found to vary as Re and Re-0.666, and are greater than these for a circular cylinder at a given Reynolds number. The numerical results substantiate that a square shaped cylinder is more bluff than a circular one.
EN
Interactions between the atmosphere and the ocean determine boundary conditions for physical and biogeochemical processes in adjacent boundary layers, and the ocean surface is a complex interface where all air-sea fluxes take place and is a crucial valuable for ocean circulation and the ecosystem. We have chosen to study the differences between the relevant or most commonly used parameterizations for drag coefficient (CD) for the momentum transfer values, especially in the North Atlantic (NA) and the European Arctic (EA), using them together with realistic wind field. We studied monthly mean values of air-sea momentum flux resulting from the choice of different drag coefficient parameterizations, adapted them to momentum flux (wind stress) calculations using wind fields, sea-ice masks, as well as integrating procedures. We compared the resulting spreads in momentum flux to global values and values in the tropics, an area of prevailing low winds. We found that the spread of results stemming from the choice of drag coefficient parameterization was 14% in the Arctic, the NA and globally, but it was higher (19%) in the tropics. On monthly time scales, the differences were larger at up to 29% in the NA and 36% in the EA (in months of low winds) and even 50% locally (the area west of Spitsbergen). Comparing the values of drag coefficient from chosen parameterizations, it showed that momentum fluxes were largest for all months, in both regions with low and high winds, when the CD values increased linearly with wind speed.
EN
Ground vehicles are the main sources of noise and infrasounds in residential areas. Numerous published works are devoted to the studies of audible sound, its sources in vehicle, and development of measures to its reduction. The authors believe that the problem of infrasound occurrence and propagation in residential areas and – hence – its negative impact on humans and ambient environment is underestimated. Development of predictions and experimental methods of studying the infrasound generating mechanism and environmental monitoring of this negative factor are an urgent issue. A significant portion of acoustic emission from a vehicle comprises infrasound and low frequency range. Internal and external infrasound of vehicle were measured. A prediction model was proposed and the influence of vehicle design features on the infrasound level was estimated. Predictions of the external infrasound generating the mechanism of vehicles reveal that its frequency and level depend on driving speed, drag coefficient, vehicle body length, and Strouhal number Wheels, which execute rotation and progressive movement in airstream, are important sources of vehicle infrasound. Five wheel harmonics were calculated for motor vehicles at various driving speeds, the existing dependences are detected. It was demonstrated that the regulatory levels of infrasound can be exceeded only in residential areas adjacent to traffic flow with driving speeds higher than 80 km/h. The results of field studies of infrasound level on the streets of Moscow were presented. Recommendations on the development of environmental monitoring and main approaches to reduce infrasound in urban environment were given.
EN
The issue of the resistance to flow in open channels with vegetation has been considered by several researchers mainly experimentally, but the case of rigid emergent vegetation with linear stem arrangement is scarcely investigated. In the present work, the results are presented of an experimental investigation related to the case of rigid emergent vegetation that has been modeled by placing small rods on the bottom of a laboratory flume in aligned configuration. Tests have been executed by varying the flow rate, the bottom slope and the number and the diameter of the rods, by directly measuring the drag force exerted by the flow on a given number of rods, and the water-level profiles. A new expression has been devised for the drag coefficient as a function of the vegetation density, weakly dependent on the stem Reynolds number that allows the use of the former also in large-scale cases. The experimentally measured forces exerted by the flow on the rods have been also compared with the results obtained by applying the momentum equation in integral form to given control volumes, exhibiting a general agreement, but also showing that the use of this technique for the evaluation of the drag coefficients can give rise to not negligible errors. One of the experimental tests has been numerically simulated with the RANS technique (ReynoldsAveraged Navier–Stokes equations), and it is found that the results, mainly in terms of water-level profiles, confirm the ability of such a numerical technique in investigating this complex category of flow cases.
6
Content available remote Influence of the diffuser on the drag coefficient of a solar car
EN
The purpose of the research was to design a solar vehicle for Bridgestone World Solar Challenge competition which takes place biannually in Australia. The article, however, presents the aerodynamic research on the car body, especially on the exit diffuser. Numerous CFD simulations of different diffuser shapes were performed in ANSYS CFX software. The paper presents the results of pressure distribution on the body and velocity contours. The drag force acting on the car body is dependent on the pressure distribution. The article includes comparison of corresponding drag coefficient values for different cases. Furthermore, the variation of the lift force depending on the shape of the bodywork was also taken into consideration. The research shows that slight differences in the construction of the exit diffuser correspond to noticeable changes in the drag coefficient values (0.138 minimum, 0.168 maximum) and significant changes in the lift force (minimum 71 N, maximum 160 N).
EN
The paper presents research concerning the influence of computational domain discretization on the results of CFD analysis. Tetrahedral and polyhedral numerical mesh types are analyzed and the mesh convergence index is calculated. The obtained results are compared to the experimental measurements concerning the estimation of drag coefficient of the vehicle model. The research carried out indicates the great influence of pre-processing on the reliability of the obtained results. Moreover, the advantages of polyhedral mesh over tetrahedral mesh are pointed out in the paper.
EN
The article presents a procedure designed for identification of projectile’s trajectory model through aerodynamic coefficients estimation. The identification process is based on firing tables artificially prepared (firing tables prepared using mathematical flight model for the projectile instead of trajectories recorded on field tests) with the use of modified point–mass and rigid body trajectory models. All the necessary data, including physical parameters of the projectile and its aerodynamic characteristics are provided. The detailed results of estimation of chosen aerodynamic coefficients are presented in both visual and tabular form. The main purpose of this paper is to establish the minimum number of trajectories (as characterized in firing tables), and the permissible error of initial parameters being passed to the mathematical model that would allow the correct identification of projectile’s trajectory model.
9
Content available remote Experimental study of the flow around two finite square cylinders
EN
An experimental investigation is conducted on the air flow past two wallmounted finite length side-by-side square cylinders, each of the aspect ratio AR = 7. The cylinder center-to-center spacing ratio T/d is varied from 2 to 6, where d is the side-width of the cylinder. The cylinders are placed at three incidence angles with respect to the freestream velocity, i.e. both cylinders at zero incidence angle (case I), both cylinders at 45° incidence angle (case II), and one cylinder at zero incidence angle with the other at 45° incidence angle (case III). The pressure distributions on the surfaces of the cylinders are measured at Reynolds numbers of 5.9 × 104–8.1 × 104. In addition, the flow structures are visualized in a smoke wind tunnel at the Reynolds number of 2 × 103. Depending on the flow characteristics, four flow structures are identified at the mid-height of the cylinders, namely the asymmetric flow, antiphase shedding flow, leading-edge separated flow and wedge flow. The sectional drag near the bottom is more sensitive to T/d than that near the top. The sectional drag coefficient measured at 0.5d below the mid-span can represent the surface-averaged drag coefficient on the entire cylinder.
EN
The paper discusses a numerical investigation, using a CFD tool, ANSYS FLUENT, of drag acting on a motorcycle helmet. The simulations were performed on a model of a helmet downloaded from a free CAD model library. A solid model enabled us to generate a mesh, to define boundary conditions and to specify a model of turbulence. Accordingly, the values of forces acting on individual sections of the helmet were obtained and the coefficients of aerodynamic drag were calculated. The test results can be used to optimize the shape of the existing motorcycle helmet construction and to study the impact of generated drag forces on reaction forces affecting a motorcyclist’s body.
PL
W artykule przedstawiono wyniki analizy porównawczej współczynników oporu uzyskanych na postawie wyników badań strzelaniem i symulacji numerycznych. Wyniki obliczeń numerycznych przeprowadzone metodą CFD z wykorzystaniem oprogramowania Ansys Fluent v16, posłużyły m.in. do opracowania wstępnych tabel strzelniczych dla nowoprojektowanych pocisków do moździerza RAK.
EN
Results of comparison between drag coefficients established by the firing tests and numerical simulations are presented in the paper. The results of numerical calculations carried out by CFD method, exploiting Ansys Fluent v16 software, were used to develop initial firing tables for newly designed projectiles for RAK mortar.
EN
This paper presents an analysis of aerodynamic characteristics of the rocket target for the final training of shooting at aerial targets by the „Stinger” system service staff. The governing equations of fluid dynamics are presented and the computational model of airflow around the rocket is developed. ANSYS CFX computational fluid dynamics software is used to compute airflow velocities, pressure, the drag force and the drag coefficient. A practical implementation of the research is presented. Taking into account the simulation results, the rocket-target was designed and manufactured.
EN
It has been shown that developing a supercavitating flow around under-water projectiles has a significant effect on their drag reduction. As such, it has been a subject of growing attention in the recent decades. In this paper, a numerical and experimental study of supercavitating flows around axisymmetric cavitators is presented. The experiments are conducted in a semi-open loop water tunnel. According to the Reynolds-Averaged Navier-Stokes equations and mass transfer model, a three-component cavitation model is proposed to simulate the cavitating flow. The corresponding governing equations are solved using the finite element method and the mixture Rayleigh-Plesset model. The main objective of this research is to study the effects of some important parameters of these flows such as the cavitation number, Reynolds number and conic angle of the cavitators on the drag coefficient as well as the dimensions of cavities developed around the submerged bodies. A comparison of the numerical and experimental results shows that the numerical method is able to predict accurately the shape parameters of the natural cavitation phenomena such as cavity length, cavity diameter and cavity shape. The results also indicate that the cavitation number declines from 0.32 to 0.25 leading to a 28 percent decrease in the drag coefficient for a 30° cone cavitator. By increasing the Reynolds number, the cavity length is extended up to 322% for a 60° cone cavitator.
EN
Two-dimensional flow analysis around NACA 23012 profile with trailing edge modification was performed. The influence of the Gurney Flap height was investigated. Obtained results were verified based on experimental data. An increase of the lift coefficient was observed with the increase of the flap height.
PL
Przeprowadzono dwuwymiarową analizę struktury przepływu wokół profilu lotniczego NACA 23012 ze zmodyfikowaną krawędzią spływową. Przebadano efekt zastosowania modyfikacji Gurney Flap o różnych wysokościach. Otrzymane wyniki zweryfikowano na podstawie danych eksperymentalnych dla badanego profilu. Stwierdzono przyrost współczynnika siły nośnej wraz ze wzrostem wysokości zastosowanej modyfikacji.
PL
W pracy zaprezentowano sposób wyznaczania parametrów ruchu gąsienicy w oprogramowaniu MES – ABAQUS 6.11 oraz współczynników niezbędnych do opisu dynamiki w oprogramowaniu SolidWorks Flow Simulation. Wy-znaczono parametry ruchu charakterystycznych punktów gąsienicy. Otrzymane wyniki porównano z założonym modelem matematycznym i wykorzystano do opisu kinetyki gąsienicowego robota inspekcyjnego. Zastosowanie oprogramowania CFD pozwoliło na wyznaczanie współczynnika oporu hydrodynamicznego, dokładnej powierzchni czołowej robota oraz objętości.
EN
In this article the problem of determining the coefficients, required to describe the kinetic underwater robots with crawler drive, was described. In this paper analysis of the movement of the caterpillar in the software MES – ABAQUS 6.11 and the movement of underwater robot in SolidWorks Flow Simulation, was presented. Parameters of the movement of the characteristic points of the caterpillar were obtained in simulation. The CAD soft-ware with CFD modules was used to determine the necessary parameters.
PL
Przedstawiono proces walidacji modelu obliczeniowego przeznaczonego do wyznaczania współczynnika oporu aerodynamicznego pojazdu MuSHELLka. Walidację przeprowadzono na podstawie badań doświadczalnych wykonanych w tunelu aerodynamicznym.
EN
Described is a method to validate numerical model designed to determine the drag coefficient of the vehicle MuSHELLka. The validation procedure followed experimental tests performed in the wind tunnel.
17
Content available remote O zależności współczynnika oporu aerodynamicznego od prędkości jazdy
PL
Na wielkość sił oporu aerodynamicznego samochodu wpływają oddziaływania o charakterze konwekcyjnym, wynikające z rozkładu ciśnień wokół pojazdu, oraz dyfuzyjnym, związane z tarciem (lepkim) powietrza. Wielkość i wzajemne proporcje obu rodzaju sił zależą od prędkości opływu powietrza wokół pojazdu, a więc w przybliżeniu od prędkości jazdy samochodu. Siły wynikające z oddziaływań konwekcyjnych zależą od kwadratu prędkości ruchu, a te zwiazane z oddziaływaniami dyfuzyjnymi zależą liniowo od prędkości jazdy. Wyznaczając współczynnik oporu w oparciu o siłę oporu otrzymaną z badań tunelowych, popełniamy błąd, standardowo przyjmując kwadratową zależność od prędkości jazdy. W artykule kwestia ta jest badana z wykorzystaniem symulacji komputerowych, a stosowna zależność współczynnika oporu aerodynamicznego od prędkości jazdy zostaje zweryfikowana.
EN
On the aerodynamic drag magnitude for a road vehicle affect the convective contributions resulting from the pressure distribution about a vehicle, and the diffusive contributions connected with the surface friction of (viscous) air. The magnitude and mutual relations of the shear and pressure forces are closely dependent on the air flow velocity over a vehicle, and approximately, on the driving speed. Forces resulted from convective contributions depend on the square of the driving speed, and those connected with diffusive contributions depend linearly on the speed. Determining the drag coefficient based on the drag force obtained from a wind-tunnel testing, we make an error routinely assuming the square dependency on the driving speed. In article, this question is considered with help of numerical simulations, and the appropriate dependency of the drag coefficient on the driving speed is verified.
EN
The converging-diverging structure is introduced to extend the lower limit of measurement of vortex flowmeters. As a compact device, the converging-diverging vortex flowmeter is proposed and designed, and its performance is studied experimentally. It is found that, first of all, an up to 51% extension of the lower measurement limit can be realized through the converging-diverging structure, compared with conventional vortex flowmeters; second, the converging-diverging vortex flowmeter with a trapezoidal bluff body has a larger Strouhal number and smaller pressure loss. The results suggest that the converging-diverging vortex flowmeter provides an alternative device especially suitable for the measurement of low-velocity fluids.
19
Content available remote Pomiar współczynnika oporu i czynnika kształtu cząstek typu flok
PL
W literaturze brak informacji nt. współczynnika oporu cząstek typu flok. W tej pracy zmierzono współczynnik oporu metodą stanu nieustalonego i metodą stanu ustalonego oraz porównano wyniki obu metod. Na podstawie współczynnika oporu zidentyfikowano sferyczność w oparciu o równanie Haidera, Levenspiela. Stwierdzono, że zastosowanie teorii przepuszczalności Brinkmana daje lepszy opis współczynnika oporu dla cząstek typu flok.
EN
Drag coefficient of floe type particles is poorly described in literature. In this work drag coefficient was measured by two methods - unsteady state and steady state and the results were compared. On basis of drag coefficient the particle sphericity was identified using the Haider and Levenspiel formula. It was found that a better description of drag coefficient for floe particles was obtained using Brinkman's theory of permeability.
20
Content available remote Argument of separation at upgrading in the JIG
EN
The necessary condition of distribution of heterogeneous feed to be separated in the pulsating water stream is constituted by the sufficient loosening of particles. Due to the variety of material, both from the point of view of its physical and geometrical properties, the stratification of particles will occur according to settling velocity of particles. The paper presents various approaches to the problem of motion in the liquid medium by a model particle, i.e. a sphere, and an irregular particle, considering the shape and drag coefficients. Interesting and at the same time different is the way of theoretical calculation of the drag coefficient for a sphere according to Finkey for the liquid disregarding viscosity, and according to Abraham, considering the boundary layer which is conditioned by the existence of liquid internal friction forces. After a thorough analysis of the methods, presented by different authors and considering the calculation of the drag coefficient for a spherical particle, taking into account the empirical dependences of the drag coefficient upon Reynolds number, the value […]= 0,46 was assumed for the drag coefficient, calculated from the formula given by Abraham and consistent with experiment. In the paper the final formula was derived which describes the terminal settling velocity of an irregular particle and which includes the particle projection diameter, reduced density and particle shape coefficients [...].
PL
Warunkiem koniecznym rozdziału nadawy niejednorodnej kierowanej do separacji w pulsującym strumieniu wody jest dostateczne rozluzowanie ziaren. Ze względu na różnorodność materiału, zarówno pod względem właściwości fizycznych i geometrycznych, stratyfikacja ziaren będzie zachodzić według prędkości opadania poszczególnych ziaren. W artykule przedstawiono różne podejścia do zagadnienia poruszania się w ciekłym ośrodku ziarna modelowego - kuli oraz ziarna nieregularnego z uwzględnieniem współczynnika kształtu i współczynnika oporu. Ciekawy a zarazem odmienny jest sposób teoretycznego wyliczenia współczynnika oporu dla kuli według Finkeya dla cieczy bez uwzględnienia lepkości i według Abrahama z uwzględnieniem warstwy przyściennej uwarunkowanej istnieniem sił tarcia wewnętrznego cieczy. Po wnikliwej analizie metodyki przedstawionej przez różnych autorów dotyczącej wyliczania współczynnika oporu dla ziarna sferycznego, z uwzględnieniem zależności empirycznych współczynnika oporu od liczby Reynoldsa przyjęto dla współczynnika oporu wartość […]= 0,46 wyliczoną ze wzoru podanego przez Abrahama i zgodną z doświadczeniem. W pracy wyprowadzono końcowy wzór opisujący graniczną prędkość opadania ziarna nieregularnego, który wiąże w sobie średnicę projekcyjną ziarna, gęstość zredukowaną oraz współczynniki kształtu ziarna […].
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