Zhi Guo Zhang

Application of Dynamic Mesh in Analysis of Propeller Hydrodynamic Characteristics

This paper presents a numerical procedure to investigate the hydrodynamic performance and flow field of propeller with the aid of dynamic mesh. The purpose of the study is to validate a hybrid mesh generation strategy and dynamic mesh technology. Computations were performed at various advance ratios following experimental conditions. Results for both global and local flow quantities are discussed and compared with experimental data. The predicted thrust and torque are in good agreement with the experimental values. The overall results suggest that the present approach is practicable for actual propeller design procedure.

Improve the Free-Piston Stirling Engine Design with High Order Analysis Method

Stirling engine is a heat engine which is enclosed a fixed quantity of permanently gaseous fluid as the working fluid. The free-piston Stirling engine is noted for its high efficiency, quiet operation, long life without maintenance in ten years and the ease with which it can use almost any heat source. Stirling cycle analysis method has been successfully applied to improve the free-piston Stirling engine design by its step-by-step development on order. This study presents the development and application of Stirling cycle analysis method. Discussions about use of multi-dimension CFD software simulating free piston Stirling engine when there’s not any available experimental data for its design will provide. Since it needs less computing resource and time to get 1D simulation results with some accuracy, the application of multi-dimension CFD could be very helpful to improve accuracy of 1D result with the details of the different simplified model parameters used in 1D model. The research demonstrates that with the combination of high order Stirling cycle analysis method, the design of the free-piston Stirling engine with the aid of numerical method could be much more effectively and accurately.

Optimization of Valve Block Shape Using CFD

Stop valves are commonly used as fluid flow control equipments in many engineering applications. A numerical study of a three-dimensional, complex geometry, stop-check valve was performed for model validation and improved understanding of valve flow features. This paper has provided a numerical investigation of the fluid flow inside a stop valve, including the modeling and the simulation of the stop valves. According to the simulation result of original valve structure, two cone valve block shape with different gradient are presented to bring some optimization to the stop-valve. CFD simulations were conducted for different structure of the valve to verify the performance of the valve after redesign the internal flow structure. The simulation results show that the pressure drop vortex strength, maximum velocity and velocity nonuniformity of valve outlet had been reduced obviously. Furthermore, the results of the three-dimensional optimization analysis of valve shape can be used in the design of low noise and high efficiency valve for industry.

Numerical Simulation of Turbulent Driven Secondary Flow in a 90° Bend Pipe

The numerical simulation of the developing turbulent flow through a three-dimensional curved pipe with strong curvature is presented. This numerical simulation is to investigate the flow structure of pipe-flow through a 90° bent pipe with the aid of RNG k-ε turbulence model, which had been well validated for high screwed curvature flow. Dean Motion downstream of the bend are found and presented. And the numerical result demonstrates that Dean motions co-exist with large scale swirling motions inside the bend pipe. Snapshot of velocity and pressure reveals that the structures found upstream of the bend persist after the bend and survive the strong secondary motions induced by the pipe curvature.

Prediction of Surface Ship's Residual Resistance Coefficient Using Neural Networks

The Holtrop method, which provides a prediction of the components of surface ships total resistance, is widely used at ships initial design stage for estimating the resistance. In this paper a neural network model which performs the same role as the Holtrop method is presented to predict the residual resistance. A multilayer perceptron has been trained with the data generated by the Holtrop method to learn the relationship between the input (length-displacement ratio, prismatic coefficient, breadth-draft ratio and Froude number) and the target variable (the residual resistance coefficient). The results of this model have been compared against those provided by the Holtrop method and it is found that the quality of the prediction is improved over the entire range of data. The neural network provides an accurate estimation of the residual resistance with the Froude number and the hull geometry coefficients as variables.

Numerical Simulation of MEMS Stirling Cooler

The heat transfer and the fluid dynamics characteristics of subsonic gas flows through micro-channels are examined using numerical method. Detailed analysis on the Stirling MEMS device has been examined for the feasibility of the performance. The 1-D Stirling engine design code was utilized to provide basic information to meet the design parameters and criteria. Furthermore a 2-D CFD code has been used to perform a detailed analysis. The simulation results show that the numerical method used here could be used for the prediction of MEMS performance before experimental test and manufacture process start.

Influence of Porous Media Property on Stirling Engine Performance

Porous medium is playing an important role in technological advances nowadays. They exist everywhere in nature and were widely used in lots of engineering projects due to their huge internal surface area and ultrafine pore size. These properties allow them to achieve good performances in heat and mass transfer. So, the regenerator of Stirling Engine uses porous medium as the matrix to get higher heat transfer efficiency. In this study, the regenerator of a 55W Stirling engine was calculated using the 1D numerical model to find the most efficient porous media from kinds of options with different structures and different parameters.

Development of Numerical Method for Prediction of Maneuvering Performance of Marine Vehicle

Numerical maneuvering tank (NMT) is developed which could be used for investigating the flow physics involving the interaction of the flow shed from the sail and the cross-flow boundary layer of the hull, interaction between the hull and appendages like rudder and propeller during maneuvering operation. Two numerical codes are used for this study: CADMV (computer aid design of marine vehicle) and FLUENT commercial code. They are validated against each other and compared with experimental measurement results. Pressure coefficient and skin friction coefficient are obtained and compared with experimental data available in the literature. The simulation results show good agreement with the experimental data. NMT was developed based on above numerical method to simulate the circular motion of marine vehicle. The steady, uniform flow fields are obtained and the characteristics of rotation flow show good agreement with actual phenomena. The circular motion simulations of a SUBOFF in NMT is conducted at different angle of drifts of hull. The obtaining of hydrodynamics parameters is very important for accurately predicting the hydrodynamic behavior of a maneuvering marine vehicle in turning motion.

The Numerical Simulation of 2D Sloshing Tank

In this study, a two-dimensional numerical method based on the volume of fluid method is used to solve for water sloshing. The 2D equations of fluid motion are derived in a moving coordinate system. For modeling impact pressure induced by large amplitude sloshing, an emphasis is given to the numerical treatment of the free surface, which is sensitive to the simulation. Liquid sloshing inside a rectangular tank is simulated. The time histories of the free surface shape and the dynamic pressure inside the tank are obtained. The results are compared with an experimental data. These comparisons show that this method can be used to simulate the sloshing induced impact loads. Then series of violent sloshing phenomenon is given and compared.

Numerical Study of Cavitation on Hydrofoils

Based on CFD technology, flow around a 2-dimentional hydrofoil of highly skewed propeller and NACA series hydrofoils are simulated using 2D incompressible Navier-Stokes equation with Realizable k- turbulence model. In the numerical simulation, the vapor volume fraction is calculated for different cavitation numbers and angles of attack by adding the mixture model. The hydrofoil’s performance and the relationship with hydrofoil parameter are qualitatively analyzed. Special focus is given to the influence of the cavitation numbers and angle of attack on cavitation characteristics.