CFD Theory Research Articles

Anti-rolling analysis and resistance optimization of a new anti-rolling hydrofoil for the trimaran vessel

The roll motion performance of the trimaran vessel is not as good as expected at low forward speed in high sea conditions. A new designed anti-rolling hydrofoil is proposed, which connects the main hull and the side hull below the waterline to provide the reverse roll moment by the huge hydrodynamic pressure during the roll motion. The anti-rolling effect of four creative schemes of the hydrofoils are analyzed by a set of high-precision numerical calculation method combined with CFD and 3D potential flow theory for roll damping and roll motion in waves. The roll damping characteristics and the mechanism of the hydrofoil are analyzed in detail combined with flow field analysis. The results indicate the high anti-rolling efficiency for the trimaran vessel. In order to make this device close to the engineering application, the profile and angle of attack are optimized to reduce the resistance. Finally, the anti-rolling hydrofoil with a good comprehensive performance is obtained, providing a valuable reference for the seakeeping design of the trimaran vessel.

Simulating the mechanically driven compressor of a marine diesel engine by CFD theory

This paper presents a flow analysis model through a mechanically driven compressor of the supercharger. The object was a centrifugal compressor directly driven from the engine crankshaft, which was used to increase the intake gas. The initial conditions for the compressor simulation were estimated based on the working relationship between the engine and its compressor, the geometry model was completed by CFturbo software, thereafter the fluid dynamic was simulated in the Ansys Workbench environment, which was based on CFD theory. The simulation results showed the relationships among the intake mass flow through the compressor and technical parameters such as the compressor efficiency and pressure ratio. The results can be applied to improve the efficiency of mechanically driven compressors in practical operation.

Simulating the mechanically driven compressor of a marine diesel engine by CFD theory

This paper presents a flow analysis model through a mechanically driven compressor of the supercharger. The object was a centrifugal compressor directly driven from the engine crankshaft, which was used to increase the intake gas. The initial conditions for the compressor simulation were estimated based on the working relationship between the engine and its compressor, the geometry model was completed by CFturbo software, thereafter the fluid dynamic was simulated in the Ansys Workbench environment, which was based on CFD theory. The simulation results showed the relationships among the intake mass flow through the compressor and technical parameters such as the compressor efficiency and pressure ratio. The results can be applied to improve the efficiency of mechanically driven compressors in practical operation.

Analysis of pressure wave signal generation in MPT: An integrated model and numerical simulation approach

Mud pulse telemetry (MPT) is one of the essential means to ensure a high transmission rate of downhole data. Continuous-wave mud pulse has a high transmission rate, strong stability, and outstanding adaptability, the most widely used downhole data transmission mode. One factor that restricts the high transmission rate of downhole data is the quality of the pressure wave generation signal. However, there is a lack of complete mathematical modeling research methods. Based on CFD theory, a numerical model of the integration of pulse generator and upstream and downstream pipelines was established for the first time, as well as the corresponding grid division process, which was to simulate the pressure wave generation and propagation process under drilling conditions, and the sensitivity analysis of parameters was carried out. The results show that the pressure drop curve derived from the thin-wall throttling theory is not the actual pressure wave, so the optimization results have a particular theoretical error. In fact, with the periodic change of the flow area, the upstream and downstream synchronously generate compression waves and expansion waves, which propagate and gradually decay. The amplitude of pressure wave increases with the increase of displacement and density but decreases sharply with the increase of gap height. Meanwhile, the amplitude does not change with the frequency and viscosity, but it aggravates the propagation attenuation of the pressure wave. Moreover, it is observed that the pressure wave is not a perfect sine wave in the case of sinusoidal rotor rotation, which needs further study. The research results of this paper provide a technical means for the optimization of downhole pressure wave generation, transmission, and noise reduction and help improve the transmission rate of downhole data.

Computational Fluid Dynamics Modeling of Hollow Membrane Filtration for Concentration Polarization

Based on CFD and film theory, filtration’s two-dimensional CFD model of the hollow membrane was established by integrating the mass transformation and the hydrodynamic transportation. Parameters of concentration polarization in the membrane channel (i.e., solute mass concentration, concentration polarization factors, and concentration polarization layer thickness) were estimated under different hydraulic conditions. In addition, the algorithm for the thickness of the concentration polarization layer has been improved. The results showed that decreasing the feed Reynolds number or increasing the transmembrane pressure can enhance the concentration polarization phenomena. Concentration polarization parameters increased sharply at the initial place (X/H < 25, where H is the entrance width, X is the distance from entrance) and then flatten out (X/H > 25) along the membrane channel; solute concentration and concentration polarization factors were arranged in a U-shape in the membrane channel’s cross-section. The improved algorithm could match well with cross section data, δ2H at X/H = 1, 25, and 200 are 0.038, 0.11, and 0.25, respectively, which can reasonably reflect the distribution of the concentration polarization phenomenon in the membrane channel.

Experimental and numerical study on coal dust ignition temperature characteristics and explosion propagation characteristics in confined space

ABSTRACT In order to reveal the ignition characteristics and explosion propagation characteristics of coal dust, a kind of coal dust cloud is studied through the experiment and numerical simulation in confined space. The result indicated that the particle size of coal dust has a significant impact on the ignition characteristics of coal dust cloud. CFD theory is used to simulate the explosion propagation characteristics in the straight and bifurcated pipelines. It is found that the flame propagation simulation result is consistent with the experimental result. In the bifurcated pipeline, from the time of 0.2 s to 0.8 s after the explosion, the flame propagates through the bifurcated pipeline. It also revealed that the flame propagation intensity of coal dust explosion in the bifurcated pipeline is affected by the structure of the pipeline, which provides a reference for the study of the propagation characteristics of coal dust explosion.

Numerical investigation on hydrodynamic performance of a novel shaftless rim-driven counter-rotating thruster considering gap fluid

Shaftless rim-driven thruster (RDT) has recently become the research focus for marine propulsion, primarily due to low vibration, low noise, and energy saving as its advantage. This study is based on CFD theory and used the Ansys-Fluent software to examine the hydrodynamic performance of a novel rim-driven counter-rotating thruster (RDCRT). It takes a No.19A+Ka4-70 duct propeller and a 20 kW RDT as examples, as it verifies the feasibility of the simulation method. It establishes three geometric models for RDCRT's hydrodynamic performance to determine whether it is necessary to consider the motor stator/rotor gap. It examines the flow distribution characteristics of the gap fluid friction force and flow channel and investigates the gap's influence on the hydrodynamic performance. Relevant case studies indicate that, when considering the gap, the calculation outcomes of the simulation model are between the stationary model and the rotational model of the rotor inner wall when ignoring the gap. In the Forward and Aft regions, the total frictional power of the gap channel correspondingly accounts for 1.7% and 1.35% of the rated power. Additionally, compared to situations with a gap, the pressure coefficient of the inner surface of the Forward and Aft rim without a gap is more significant. Thus, the hydrodynamic simulation model should not ignore the gap. For the RDCRT, the thrust coefficient, the torque coefficient, and the maximum efficiency value are more significant than those of the single-propeller RDT, hence validating its advantages.

Research on Ignition Energy Characteristics and Explosion Propagation Law of Coal Dust Cloud under Different Conditions

To study the ignition energy characteristics and explosion propagation law of coal dust cloud, a kind of coal dust cloud is studied through experiment and numerical simulation under different conditions. The result indicated that ignition delay time and dust spray pressure have obvious effects on the minimum ignition energy of coal dust cloud. CFD theory is used to simulate the explosion flame propagation. It is found that the simulation error of flame propagation distance is acceptable and the simulation result is consistent with the experimental result. When the spray pressure is 0.06 MPa, the flame propagation distance is the farthest, indicating that the turbulence of coal dust cloud is the largest at this condition. As the ignition temperature increases, the flame propagation distance continues to increase, proving that ignition temperature has an obvious effect on the flame propagation process of coal dust cloud explosion.

Gas Diffusion Model and Its Application based on CFD Theory

In order to reduce the loss and impact of the unexpected leakage of hazardous chemicals, the paper makes use of the computational fluid mechanics theory and applies the commercial software, FLOVENT, to imitate the steady state and transient state of six scenes of the diffusion scope and concentration change of NH3 and H2 in different wind directions and leak location; furthermore, it takes the simulated result as the basis to analyze the diffusion length and impact scope of the characteristic concentration, both of which will be the evidence for occupants evacuation.

An Assessment Method of Structure Strength Analysis on Full-Scale LNG Independent Type C Tank

The sloshing induced by partial loaded in LNG (Liquified Natural Gas) independent type C tank will threat the structure of tank. The strength check of the tank plays an important role in the design of LNG tank, which can also improve the safety of the cargo containment system. Hence, an assessment method of the structure of LNG independent type C tank is presented, in which the method of one-way fluid-structure interaction is used. Sloshing load is considered with a numerical technique based on CFD theory, which can reduce large computational expense and remain a good accuracy. The dangerous conditions of sloshing pressure are determined by frequency domain analysis of the tank and ship. By computation of sloshing condition of 1000 m3 fuel bunker vessel, the feasibility of this method is explained and suggestions on structure design of tank is given.

Cross-comparative analysis of loads and power of pitching floating offshore wind turbine rotors using frequency-domain Navier-Stokes CFD and blade element momentum theory

Reliable predictions of the aero-and hydrodynamic loads acting on floating offshore wind turbines are paramount for assessing fatigue life, designing load and power control systems, and ensuring the overall system stability at all operating conditions. However, significant uncertainty affecting both predictions still exists. This study presents a cross-comparative analysis of the predictions of the aerodynamic loads and power of floating wind turbine rotors using a validated frequency-domain Navier-Stokes Computational Fluid Dynamics solver, and a state-of-the-art Blade Element Momentum theory code. The considered test case is the National Renewable Energy Laboratory 5 MW turbine, assumed to be mounted on a semi-submersible platform. The rotor load and power response at different pitching regimes is assessed and compared using both the high-and low-fidelity methods. The overall qualitative agreement of the two prediction sets is found to be excellent in all cases. At a quantitative level, the high-and low-fidelity predictions of both the mean rotor thrust and the blade out-of-plane bending moments differ by about 1 percent, whereas those of the mean rotor power differ by about 6 percent. Part of these differences at high pitching amplitude appear to depend on differences in dynamic stall predictions of the approaches.

Accident consequence calculation of ammonia dispersion in factory area

With the widespread use of ammonia in the process industry, more and more accidents were caused by ammonia leakage and dispersion. The dispersion of ammonia is determined by its physical properties, release source conditions and atmospheric environment. Full-scale numerical simulation based on CFD theory was carried out to study the dispersion law of ammonia in a food factory. It was found that ammonia concentrated on the symmetric plane and showed an upward movement near the source. Moreover, the effect of pressure on the dispersion of ammonia was explored showing that the concentration of ammonia near the source increased with the increase of pressure, while the dispersion of ammonia far from the source is mainly influenced by wind field. Last but not the least, the dangerous area completely covers the obstacle region according to the harmful concentration, but the lethal concentration range and explosion range both only existed near the release source. Correspondingly, the concentration of ammonia in the region far from the symmetric plane can be regarded as a safe area. When the accident happens, one should stay away from the release source and evacuate towards the sides in a timely manner. We hope that this work can provide an effective method in predicting the impact of ammonia dispersion and can arouse concerns over the public safety.

Current Situation and Prospect of Erosion Wear

The material loss and equipment failure caused by erosion wear is a serious problem in solid-liquid mixture flow in the mechanical, metallurgy, energy, building materials, transportation, aviation, aerospace, military and other industrial departments. Therefore, understanding the erosion wear mechanism, the influencing factors, and how to set up mathematical model are very important. Since the 1950s, the research on the erosion wear made great development. The purpose of this paper is to give a comprehensive review about previous research work of erosion wear. Firstly, the mechanism and influencing factors of erosion wear are introduced. Secondly, the forces of particle caused by fluid are analysed and several erosion models which tested by experimental with good results are introduced. Thirdly, the method of erosion numerical simulation combining computer software and CFD theory is introduced. Finally, based on the conclusion, some useful conclusions are drawn and the future research direction is prospected.

Semi-submersible Offshore Coupled Motion in Irregular Waves

In order to predict the hydrodynamic performance of semi-submersible offshore platform accurately, based on CFD theory, continuous equation and N-S equation as the control equation, RNG type k-ε model as turbulence model, using the finite difference method to discretize the control equation，using the Semi-Implicit Method for Pressure Linked Equation (SIMPLE) algorithm to solve the control equation，using the VOF method to capture the free surface. The numerical wave tank of irregular wave is established, and the wave force and motion response of the semi-submersible platform under irregular wave are studied. Based on the Jonswap spectrum density function, for a certain area of two irregular waves (South China sea, a-ten-year return period, a-hundred-year return period) sea condition, five wave direction Angle (0 °, 30 °, 45 °, 60 °, 90 °), a total of 10 kinds of conditions of the motion response of semi-submersible platform are simulated, through analysis and comparison of simulation results, the influence law of wave angle, wave period and wave height on platform motion is obtained. Compared with the experimental values, the results of heave and pitch are close to the experimental data under the sea condition of 2, 0 degree wave angles. The research results in this paper can provide reference for the design and motion response prediction of practical semi-submersible offshore platforms.

Simulation and Experimental Analysis of the Temperature Field of Flow of Airport Snow Thrower Based on CFD Theory

It is a hot issue for airport users and researchers to pay attention to the influence of the hot air flow generated by the hot blowing snow thrower on the durability and service life of the pavement. In order to clarify the influence of hot air flow generated by hot blowing snow throwers on the temperature distribution of airport runway, this paper studies the temperature distribution of airport runway under the action of hot air flow generated by hot blowing snow throwers by CFD simulation and design of field measurement experiments. The results show that the maximum temperature of the surface obtained by the simulation method is 554.21K, the limit temperature of the surface is 539.75K and the average temperature difference is 22.64K, which verifies the accuracy of the simulation model. In view of the research results, in order to promote the application of this type of snow thrower in the airport, it is necessary to verify whether the airport roadway can withstand the action of high temperature airflow of 539.75K.

Simulation and Experimental Analysis of the Temperature Field of Jet Flow of Aircraft Based on CFD Theory

As a key indicator of airport concrete pavement, the durability of concrete is seriously affected by the jet flow generated by aircraft engines. In order to clarify the temperature field distribution of aircraft jet flow acting on the pavement surface, this paper obtained the temperature field distribution of pavement surface under the action of three types of aircraft jet flow by combining field test experiment and CFD simulation. CFD simulation adopts the shear stress transfer model which is often used in engineering problem calculation, and the field test experiment adopts the method of embedding temperature sensor in precast concrete slab. The paired two sample t test was used to test the difference between the experimental results and the simulation results. The experimental results show that the pavement temperature increases first and then decreases with the distance from the engine, and reaches the maximum at the intersection point of the jet flow and the airport pavement. The simulation curve is in good agreement with the experimental results. When the level of confidence is 0.01, there is no significant difference between the simulation value and the experimental value, which verifies the accuracy and feasibility of the simulation calculation model. The simulation results of the three aircraft showed that when type C aircraft is in the state of full afterforce, the maximum pavement temperature is the highest which is 22m away from the nozzle, and can reach 533.81K. The current work provides a new method for measuring the temperature distribution of airfield pavement under the action of jet flow and a basis for the application of fiber concrete in airfield pavement.

Optimized Design on the Disc Stack of Lubricating Oil Separator Based on CFD Theory and Orthogonal Experiments

ABSTRACT Zhao, Z.; Peng, G.; Feng, M., and Liu, J., 2018. Optimized design on the disc stack of lubricating oil separator based on CFD theory and orthogonal experiments. In: Liu, Z.L. and Mi, C. (eds.), Advances in Sustainable Port and Ocean Engineering. Journal of Coastal Research, Special Issue No. 83, pp. 335–342. Coconut Creek (Florida), ISSN 0749-0208. The recycle and reuse of lubricating oil have social and economic benefits. To optimize the design, it is important to study the inner flow field of lubricating oil separator with numerical method. Because of the error in the traditional empirical equation, the configuration of the disc stack is optimized in 9 experimental projects to achieve the best configuration through numerical simulation. The result shows that the efficiency of the calculation and separation meet the demand of the design, the calculated separation efficiency is slightly higher than the actual efficiency with a difference of 1.5% in oil-water separation and a difference of 1.4% in...

Paint thickness simulation for robotic painting of curved surfaces based on Euler–Euler approach

The purpose of this paper is to provide a method of the paint thickness simulation for robotic painting of curved surfaces based on the Euler–Euler approach in CFD theory. The Euler–Euler approach is proposed to be adopted to simulate the paint deposition process of painting curved surfaces with a moving spray gun in this paper. The paint deposition model established comprises two parts: a two-phase spray flow field model and a film model. The method of solving the model is also provided. In order to demonstrate the capability of the proposed method, three cases were simulated and experimented including painting a flat plate, an outer cylindrical surface and an inner cylindrical surface. It was found that the peak of the film thickness distribution on the inner cylindrical surface is the largest followed by that on the flat plate and that on the outer cylindrical surface. The film width of painting the inner cylindrical surface is wider than that of the outer cylindrical surface and the flat plate. The experimental results were in a reasonable agreement with the simulation results, which indicates the simulation method based on the Euler–Euler approach in CFD theory proposed in this paper to be effective and applicable in simulating the paint thickness for robotic painting of curved surfaces.

Numerical Simulation Analysis of Cavitation Performance of Tandem Propeller

The steady non cavitation hydrodynamic characteristics of CLB4-55-1 tandem propeller and the steady cavitation flows of NACA66 hydrofoil are numerically studied firstly based on the RANS equations of homogeneous multiphase using CFD theory, combined with the SST k-ω turbulent model and Z-G-B cavitation model. Numerical simulation results are in good agreement with the experimental results, which indicates that the numerical method is reliable and accurate. Then, the cavitation performance of the tandem propeller are numerical simulated and analyzed. The results show that the computational model can predict the cavitation performance of tandem propeller accurately. The cavitation performance of tandem propeller is nearly the same as single propeller, however, the cavitation phenomenon of back propeller is greater than the head propeller at certain advance coefficient and cavitation number. The cavitation phenomenon will disappear with the increase of the advance coefficient or the cavitation number.

A Deterministic Sensor Deployment Method for Target Coverage

In order to monitor the gas leakage, the gas sensors are deployed conventionally in chemical industry park, with little considerations given to the gas characteristics and weather conditions, which give rise to the problems of coverage hole and coverage repetition. To solve the problems, this paper proposes a deterministic sensor deployment method with the gas diffusion models which takes into account wind speed and direction and then studies the influence of wind speed and direction on the monitoring error of gas sensors. Then, we research the deterministic deployment method of gas sensors in condition of the main wind speed and direction somewhere. Firstly, we use the CFD theory to simulate the gas diffusion situation so as to obtain the concentration value of the relevant points. Secondly, we put forward a new optimization criterion, namely, the more alarm concentration points covered by gas sensors, the coverage performance is better, and the deployment method is better. Accordingly, a new objection function is built. Thirdly, we obtain the weight values of the function using entropy estimation method. Finally, we deploy the gas sensors determinately using particle swarm optimization (PSO) algorithm. The simulation results show that the proposed method can improve the monitoring efficiency and the coverage performance of gas sensor network.