CFD Method Research Articles

Calculation of Hydrodynamics Resistance Coefficient of Diver by CFD Method at Free Surface Condition

Calculation of Hydrodynamics Resistance Coefficient of Diver by CFD Method at Free Surface Condition

An improved vacuum-steam pulsed blanching machine design and garlic scape blanching verified experiment

Vacuum-steam pulsed blanching (VSPB) is an emerging blanching method resulting in high efficiency and product quality. However, inconvenient loading, small loading capacity, uneven rinsing and imprecise control hinder its application in food industry. Therefore, the current work aimed to design a VSPB machine, including selection of components, building a control system and designing a steam nozzle in order to increase the load capacity and improve device control. For this purpose, a horizontal blanching chamber with internal nozzle was designed and optimized using CFD method. The vacuum chamber design required a more evenly distributed steam inlet. A water-sealing vacuum pump, a cooling device and a hardware system were developed. The distribution of steam released from the nozzle in the chamber was numerically investigated by solving the three-dimensional Reynolds-averaged Navier-Stokes equations, with a velocity uniformity index value of 0.448. The validation blanching test was conducted using garlic scape as the test material. The steam holding time and the number of cycles significantly affected (p < 0.05) the color of the garlic scapes. Peroxidase (POD) activity decreased with the increase of blanching cycles until the enzymes were completely inactivated. VSPB significantly decreased (p < 0.05) the lignin content of the garlic scapes. The findings indicate that the best results were obtained after 2 cycles of VSPB and steam holding time of 30 s. Industrial relevanceHot water and steam thermal blanching are the two most frequently used blanching methods in food processing. Generally, they are used as a pretreatment before drying, freezing or canning of different fruits and vegetables. In current work, an improved vacuum-steam pulsed blanching machine was designed and the validation blanching test with garlic scape as the material indicated that VSPB operation was effective in preventing the synthesis of lignification in garlic scapes. By considering enzyme inactivation, lignification, color, and other quality attributes, 2 cycles of VSPB and steam holding for 30 s were proposed as the optimal VSPB conditions.

Resistance on Catamaran Decommissioning Unit: A Comparison of Numerical Analysis (Two Turbulence Models) to Model Test Result

A new concept design Catamaran Decommissioning Unit has been developed by Research Center for Hydrodynamics Technology Indonesia. The catamaran has a unique shape, however in order to achieve resilient and sustainable the decommissioning unit as it has a unique shape, resistance analysis both model testing and numerical calculation must be conducted. The resistance value from the numerical analysis needs to be validated with the results from model testing in the towing tank. A model of a catamaran unit with a scaling factor λ=36 was taken as the object of study. The model test was conducted in a towing tank with service speed varies from 7-15 knots. As a comparison, a numerical analysis using the CFD method was being performed under two different turbulence models (k-ε and k-ω SST) with the same speed regarding the experimental speed parameter. Iin a conclusion, numerical analysis with k-ω SST turbulence model gives a better performance with smaller relative deviation compared to the k-ε turbulence model.

마이크로 터보제트 엔진의 터보팬 파생개발 연구

A study to modify and develop a turbofan engine using a micro turboprop engine has been conducted. The turbofan engine has been designed by adding a fan blade module as well as other required accessories to the existing turboprop engine. CFD and FEM methods were used for numerical analyses of the additional fan module to assess its aerodynamic performance and structural stability. Components of the fan module were fabricated with consideration for manufacture and assembly, and a test rig was also designed and built to measure the turbofan engine performance. The performances of the turbofan engine were measured and compared to an existing micro-turbojet engine. The performance tests were conducted in two phases: In the first phase, the robustness of the designed turbofan and test rig were investigated and in the second phase, the maximum power test has been conducted to measure performance variables such as engine thrust, engine exhaust temperature(EGT) and fuel flow rate according to the engine RPM. The test results indicated that the turbofan engine SFC was reduced by 40∼50% of the existing turbojet engine, demonstrating the successful implementation of turbofan characteristics.

A New Method of Identifying the Aerodynamic Dipole Sound Source in the Near Wall Flow

Consider that the sound dipole source in the flow field is composed of multiple micro-spherical oscillating sources. An aerodynamic sound source identification method is established by the relationship among the oscillating source, the radiated sound pressure, and the pressure gradient of flow in the near-wall flow field, and the formula for calculating the sound power of the sound dipole source in unsteady flow is derived. It shows that the power of sound dipole sources is proportional to the square of the oscillating force or pressure gradient. The combination of the formula and CFD method is further applied to the flow around the cylinder, which clearly presents the sound power and location characteristics of sound dipole sources. Further, the relationship between the sound source and the flow separation, or flow vortex shedding, is analyzed. The corresponding correlation analysis is also carried out, which indicates that the sound dipole source exists in a finite area of the attached wall. The front end of the area is at the separation point along the circumferential direction of the wall, and the end is at the location where the separation vortex completely falls off and a trailing vortex begins to form. In addition, the thickness of the area exists along the radial direction and gradually increases backward.

Study on fast prediction method of hydrodynamic load of floating horizontal axis tidal current turbine with pitching motion under free surface

The floating horizontal-axis tidal current turbine (HATCT) moves with the floating carrier while rotating, resulting in a change in its relative inflow velocity at any time. If the rotating speed of the HATCT is fixed, the HATCT cannot work at the optimum tip speed ratio, resulting in the failure to achieve the optimum power generation efficiency. Therefore, this paper proposes a control strategy for the rotating speed of the HATCT, and obtains the hydrodynamic loads of the HATCT with variable speed rotation and pitching motion under free surface conditions based on the CFD method. Compared with the hydrodynamic load of the HATCT under the same situation but with fixed speed control, the variable speed control can effectively improve the power coefficient of the HATCT, but the load fluctuation in terms of the inflow direction load, power, and pitch moment coefficients are more significant than those with fixed speed control. On this basis, according to the variation law of the damping coefficient with pitch period, pitch amplitude, and tip speed ratio, the hydrodynamic load prediction method of the HATCT with pitching motion is established. The validity of this prediction method is verified by comparing the results with those of CFD calculation.

Marine propeller underwater radiated noise prediction with the FWH acoustic analogy Part 1: Assessment of model scale propeller hydroacoustic performance under uniform and inclined flow conditions

This paper explores hydrodynamic performance, including cavitation and URN for the benchmark model scale propeller, The Princess Royal, operating under uniform and inclined flow conditions. In the numerical calculations, the DES method and the k-ω SST turbulence model were utilised to solve the cavitating flow around the propeller and determine the source field for the sound propagation. Also, the developed V-AMR advanced meshing technique was applied for accurately solving the tip vortex flow and hence better representation of the tip vortex cavitation in the propeller slipstream. The Schnerr-Sauer mass transfer model was used to model the cavitation on and off the propeller blades, whereas the cavitating propeller URN was predicted using the permeable formulation of the FWH equation. The numerical results were first validated with the available experimental data in model scale in a wide range of operating conditions through the propeller hydrodynamic performance characteristics, cavitation extensions and URN. Then, the numerical URN predictions were extrapolated to full-scale with the aid of the ITTC procedure to compare the CFD predictions with the extrapolated measured data obtained by different testing facilities within the scope of a recently conducted international round-robin test campaign. The results showed that the sheet and tip vortex cavitation was generally modelled successfully in the numerical calculations compared to the model-scale experimental observations in different facilities. The propeller URN predictions were in good agreement with the measured data in model scale, although some URN level discrepancies (i.e., around 5 and 10 dB) were observed between numerical predictions and model-scale measurements at certain frequencies in the low-frequency region of the noise spectrum. By taking the URN level differences measured in each facility into account, the full-scale extrapolated propeller URN predictions satisfactorily agree with the extrapolated full-scale experimental test data. Therefore, this study confirms that the CFD methods, together with the acoustic analogy, can be used for predicting the propeller URN, similar to other traditional ship hydrodynamic phenomena (e.g., resistance, self-propulsion, cavitation etc.).

Optimization of Fuel In-Situ Reduction (FISR) Denitrification Technology for Cement Kiln using CFD Method

Optimization of Fuel In-Situ Reduction (FISR) Denitrification Technology for Cement Kiln using CFD Method

Numerical simulation on heat transfer enhancement of free piston Stirling engine heater with composite cross section mini channels

Integral fin with micro-channels have been widely used in small free piston Stirling engines heater due to their high heat transfer rate, low flow loss, and high machining accuracy. A β-type free piston Stirling engine heater with composite cross section mini channels(CCSMH) is designed for heat transfer enhancement applying to solar dish power generation system. Investigation on heat transfer performance of the heater under oscillating flow is carried out by CFD method, which is compared with smooth annular tube heater. The influence of geometry parameters on the performance of heat transfer and pressure loss is investigated. A improved performance evaluation criteria PEC is proposed for the condition of equal flow velocity to evaluate the enhanced heat transfer performance of the heater. The results show that the maximum value of the comprehensive performance evaluation index PEC can reach 3.14, the maximum mean pressure drop increment of CCSMH compared with the smooth tube heater is 38.4 Pa, which is much lower than the minimum pressure of 2.3 MPa and can be neglected.

Analysis of the combustion engine exhaust system structure in aspect of shaping acoustic energy

The flow of exhaust gases is the source of many physical processes, including thermal, acoustic, mechanical and chemical phenomena with high dynamics of changes. The study analyzes the impact of the entire structure of the exhaust system on the formation of acoustic energy, determining the transmission loss characteristics of its individual components and the entire system. On the example of a structure based on a proprietary solution of an adjustable reactive muffler, the possibilities of shaping the flow of acoustic waves in the process of designing and selecting exhaust systems for internal combustion engines were determined. The study was carried out with the use of the CFD method and a specialized package for advanced simulations AVL AST.

Experiment and numerical simulation study on resistance performance of the shallow-water seismic survey vessel

In this paper, a new type of shallow-water seismic survey vessel is proposed to solve the problem that the traditional seismic survey vessels cannot satisfy the requirements of the shallow-water marine resources exploration. To reveal the influence of shallow water effect on resistance and flow field, this research is to obtain the resistance and shallow-water characteristics of this shallow-water seismic survey vessel through ship model experiments and numerical methods. Firstly, the ship model experiment predicted the resistance at different speeds in shallow water and obtained the benchmark data to validate numerical methods. Then, the CFD methods were used to calculate the resistance of the ship in deep and shallow water. The numerical results are in good agreement with the experimental results. Finally, this paper provided details of the distribution of wave, pressure and flow fields at different water depth conditions in order to explain the causes of increased resistance in shallow water, providing a reference for the shallow-water seismic survey vessel design.

Influence of air inlet distance on coal dust pollution characteristics in working environment during tunneling based on CFD method

Coal dust is one of the pollutants generated during the coal tunneling process. However, the air inlet distance will increase with the advancement of the working face, resulting in the redistribution of the air flow field, further affecting the pollution characteristics of coal dust. This effect weakens the effectiveness of dust removal equipment. Therefore, transient CFD modeling was used to study the influence of air inlet distance on air flow, dust migration distance, and dust concentration distribution in the breathing zone and achieve the highest dust reduction efficiency. Results showed that the air flow formed two reflows in the tunnel under forced ventilation. When the air inlet distance increased from 6.0 m to 8.4 m, wind flow diffusion distance (along the return side coal wall) Lp and air inlet distance d can be described as Lp = 34.272–7.108d + 0.570d2 . Furthermore, the dust diffusion time to the outlet increased from 35 s to 40 s, and the dust migration distance increased as a power function of air inlet distance. Meanwhile, the dust migration distance in the first 10 s accounted for 45–50% of that for the entire time period. In addition, the dust migration distance decreased only after 25 s, and the dust concentration in the return side breathing zone gradually increased. Finally, air curtains and dust removal fans were recommended for dust control, and the dust in the daily tunneling process can be effectively controlled when da = 15.0 m and de = 8.0 m. The dust reduction efficiency was 85.29–99.90%. The research results provide technical support for the dust outlet installation of dust extraction fans during tunneling and guidance for dust control in the similar working environment.

Numerical Investigation on Enhanced Heat Transfer with Tilted Hypervapotron Structure of the Fusion Blanket

High flux components in fusion reactor are designed to transfer high thermal loads from the core plasma under steady-state operation and emergency conditions. In order to improve the heat transfer ability, hypervapotron structure is proposed to promote the heat transfer performance by optimizing the thermal hydraulic design. In this paper, three-dimensional numerical simulation was carried out using CFD methods for the improved solution of the first wall. The results show that the heat transfer performance of the triangular fin structure with tilt angle of 30° is superior to 0 °, 15°and 45°. At a typical flow rate of 2 m/s, the heat transfer efficiency of the triangular fin with tilt angle of 30° improved by a maximum of 118.1% compared with that of the smooth flow channel. In addition, the heat transfer performance of the triangular fin structure is better than other fin structure, and its maximum temperature drops by 136.3K compared to the smooth flow channel. The design solution may provide a viable new method for efficient cooling of future fusion reactor components with high heat flux.

COMPARISON OF THE DRYER AIR INLET POSITION ON THE SPRAY DRYER WITH A DOUBLE CONDENSER TO PRODUCE A ROTATING FLOW THROUGHOUT THE DRYING CHAMBER: CFD ANALYSIS

Simulation of the drying air and the spray of liquid in the spray dryer chamber with Discrete Phase Material (DPM) and Discrete Random Walk (DRW) was presented in this study using CFD methods to analyze the drying liquid. The main problem in spray drying is the adhesion of the material to the drying chamber walls, which causes uneven drying material. This adhesion can slow down the drying process and reduce productivity. The design of the drying air inlet into the drying chamber becomes essential to research. Variations in the position of the drying air inlet into the drying chamber are carried out in the 3D spray dryer room to see the mechanism of the centrifugal velocity of the drying airflow, which can improve uniform mixing with flow resistance due to friction with small walls and the drying air velocity. This phenomenon is impossible to observe in experiments. A geometric model consisting of 1,054,000 hexa-mesh elements at the area around the nozzle, the top spot of the chamber and the remaining area covered with a tetrahedral mesh, was determined to predict velocity, temperature, and fluid flow behavior. The first position, the dryer air inlet, is at an angle from the diameter of the spray drying chamber. The second position is in the middle of the diameter of the drying chamber. The position of the first inlet produces a more even temperature contour with a more tangential velocity due to the small frictional resistance with the walls. At the same time, the second position is not recommended because the flow leads to one side of the wall and creates sticking and even material buildup. A double-heated condenser can dry air at moderate temperatures, and it is a very effective drying product— positioning the dryer air inlet into the drying chamber, achieving the economical production of high-quality products.

Examination of fuel flow through a leaky fuel unit using the experimental method and CFD computer modelling

The occurrence of an external leak in the aviation fuel unit leads to a catastrophic aviation event. The aim of the research was to estimate the flow of the fuel stream through the fuel filter chamber with its external unsealing. The research was carried out using experimental methods and computer CFD modelling. Experimental studies were carried out on a specially designed test stand. During the tests, the flow rate of the fuel stream flowing out to the environment was changed. Numerical calculations allowed to obtain the values of the stream and pressure inside the leaky filter chamber. The results of numerical calculations were compared with the results of experimental measurements. The CFD method significantly supplemented the information on the fuel flow inside the considered filter chamber at its external unsealing. The use of software based on the CFD method allows to obtain reliable values characterizing the fuel flow in the aviation fuel unit.

Experimental and numerical study of curvature effects and NO formation in ammonia Bunsen flames

Analysis of ammonia Bunsen flame is meaningful for understanding ammonia combustion details and solving the two major problems, the poor combustion characteristics and the severe NO emission. In the present work, ammonia Bunsen flames with equivalence ratio from 0.9 to 1.2 were successfully achieved at an elevated preheat temperature, 873 K, using an elevated-preheat-temperature jet flame facility. Detailed simulations were conducted using the CFD method combined with a chemical kinetic model. A good agreement was achieved between the calculated flames and the experimental flame images. The strong effects of curvature at the flame tip were revealed both experimentally and numerically, which were consistent with the literature data. In the lean Bunsen flame, curvature inhibits combustion, while, in the stoichiometric or rich flames, curvature enhances combustion. Based on the calculated flames, comparison of the detailed flame structures between the tip and the planar portion was conducted and the mechanism of the curvature effects was uncovered, which were closely related to the H2 transport characteristics. Besides, NO formation was investigated and a strong dependence on the local combustion intensity and atmosphere was observed. In stoichiometric and rich flames, two specific NO peaks were uncovered at the flame tip and on the base, respectively.

Gust Response of Spanwise Morphing Wing by Simulation and Wind Tunnel Testing

The spanwise morphing wing can change its aerodynamic shape to suit its flight environment, thereby having the potential to improve the flight performance of the aircraft, especially in gusty conditions. To investigate the potential of morphing wings, the aerodynamic performance of a spanwise morphing wing with a flapping wingtip in a gust environment was analyzed in this paper. The aerodynamic characteristics of the morphing wing are hard to measure accurately, and thus a wind tunnel test was carried out to study the influences of morphing parameters, such as the morphing length, amplitude and frequency on the gust alleviation effect. The flow mechanism of the designed spanwise morphing wing was analyzed in detail by the instantaneous lift results of the wind tunnel test and the flow field results of the CFD method. The results have shown that with appropriate morphing parameters, the spanwise morphing wing designed in this paper can effectively achieve gust alleviation during flight. The conclusions obtained in this paper can be useful guidance for the design of morphing aircraft.

A study on interaction among hull, diesel engine and propellers of a twin-screw ship during turning circle maneuver

A marine propulsion plant will experience power fluctuations during ship maneuvers. In the turning circle maneuver, the propulsive load increases significantly, and the power required by the two shafts of a twin-screw ship may be completely inconsistent. To protect the propulsion plant, the interaction between the engine and the propellers should be studied in depth. In this paper, the twin-screw ONRT ship and the 16PA6-STC diesel engine are selected as the study objects. A series of captive model tests are simulated by using CFD method to obtain the hydrodynamic derivatives and hull-propeller-rudder interaction coefficients in the MMG model. The effective wake fraction is computed under the maneuvering conditions. Turning circle maneuver of the ship is predicted by using the established MMG model, and the predicted ship maneuvering characteristics show good agreement with the available experimental results, which verifies the CFD-based modeling method. Finally, a dynamic model of hull-engine-propeller system is established on the simulation platform for evaluating the operating characteristics of propulsion plant. The propeller loads are predicted and the interaction among hull, engine and propellers is investigated. This study helps to provide a deeper insight into the engine operation behaviors during turning circle maneuver of a ship.

Application of CFD-DSMC coupling method in H2 flow and heat transfer in microtube

In the research of porous media and the interior of microelectronic devices, fluids frequently shuttle among pores and wall cracks, therefore it is of great significance to explore the influence of media wall on fluid flow and heat transfer. In this paper, CFD-DSMC coupled iterative algorithm is first used in the research of the flow and heat transfer of gas near the wall in the porous media, which simplified into the flow and heat transfer in micron-scale tube with smooth and rough wall conditions. It is found that compared with the pure CFD method, the velocity field obtained by the coupled method is quite different in the region close to the wall, and this will affect the flow field in the mainstream region, that is, with the higher roughness of the wall, the velocity in the central region will be smaller. There is no significant difference in the temperature distribution in the microtube before and after coupling, but the temperature in the mainstream decreases with the increase of the roughness of the wall. In addition, the temperature jump was found from some of the coupling results close to the wall. The results will contribute to a deeper understanding of the influence of rough surfaces on gas flow and heat transfer near the wall, and provide guidance for the regulation of flow and heat transfer in porous media.

Uncertainty Quantification of Compressor Map Using the Monte Carlo Approach Accelerated by an Adjoint-Based Nonlinear Method

Precise and inexpensive uncertainty quantification (UQ) is crucial for robust optimization of compressor blades and to control manufacturing tolerances. This study looks into the suitability of MC−adj−nonlinear, a nonlinear adjoint-based approach, to precisely and rapidly assess the performance discrepancies of a transonic compressor blade section, arising from geometric alterations, and building upon previous research. In order to assess the practicality and illustrate the benefits of the adjoint-based nonlinear approach, its proficiency and precision are gauged against two other methodologies, the adjoint-based linear approach (MC−adj−linear) and the high-fidelity nonlinear Computational Fluid Dynamics (MC−CFD) method. The MC−adj−nonlinear methodology exhibits impressive generalization capabilities. The MC−adj−nonlinear method offers a great balance between precision and time efficiency, since it is more precise than the MC−adj−linear method in both design and near-stall conditions, yet requires approximately a thirtieth of the time of the MC−CFD method. Finally, the MC−adj−nonlinear method was utilized to conduct fast UQ analyses of the section at four distinct speeds to quantify the performance uncertainty for the compressor map. It is found that aerodynamic performance is more sensitive to geometric deviations at high speeds than at low speeds. The impact of the geometric deviations is generally detrimental to the mean efficiency.