Influence of Cavity Shape on Hydrodynamic Noise by A Hybrid LES-FW-H Method

The flow past various mechanical cavity, which is a common structure on the surface of the underwater vehicle, and generating hydrodynamic noise has attracted considerable attention in recent years. In this paper, a hybrid method is presented to investigate the hydrodynamic noise induced by mechanical cavities with various shapes. With this method, the noise sources in the near wall turbulences or in the wake are computed by the large eddy simulation （LES） and the generation and propagation of the acoustic waves are solved by the Ffowcs Williams-Hawkings （FW-H） acoustic analogy method with acoustic source terms extracted from the time-dependent solutions of the unsteady flow. The feasibility and reliability of the current method was verified by comparing with experimental data （Wang, 2009）. The 2D cavity models with different cross-section shapes and 3D cavity models with different cavity mouth shapes （rectangular and circular） are developed to study the influence of cavity shape on the hydrodynamic noise. By comparing the flow mechanisms, wall pressure fluctuations, near-field and far-field sound propagation distributions, it is found that the quadrangular cavity with equal depths of leading-edge and trailing-edge is preferred for its inducing lower hydrodynamic noise than the cylindrical cavity does.

Simulation of three-phase flow and lance height effect on the cavity shape

A three-dimensional computational fluid dynamics （CFD） model was developed to simulate a 150-t top-blown converter. The ef-fect of different lance heights on the cavity shape was investigated using the volume of fluid （VOF） method. Numerical simulation results can reflect the actual molten bath surface waves impinged by the supersonic oxygen jets. With increasing lance height, the cavity depth de-creases, and the cavity area, varying like a parabola, increases and then decreases. The cavity area maximizes at the lance height of 1.3 m. Under the three different lance heights simulated in this study, all of the largest impact velocities at the molten bath surface are between 50 m/s and 100 m/s.

A Study of Cavitator Deformation and its Effect on Cavity Shape

The cavitator is the key component of a supercavitating vehicle. Based on the potential flow theory and ANSYS, we perform stress and deformation analysis of a cavitator and present a computational procedure of supercavitating shape when the vehicle was in high speed motion. Different shapes and materials models were examined to determine the deformation arid the extent of influence on the cavity shape. Information obtained from these analyses reveals that the deformation of the cavitator can be one of the causes of supereavitating vehicle failure .

Influence of the Inclination Angle on Mixed Convection and Heat Transfer in a“T”Shaped Double Enclosure

The effect of the tilt angle on mixed convection and related heat transfer in a“T”shaped double enclosure with four heated obstacles on the bottom surface is numerically investigated.The considered obstacles are constantly kept at a relatively high(fixed)temperature,while the cavity’s upper wall is cooled.The finite volume approach is used to solve the mass,momentum,and energy equations with the SIMPLEC algorithm being exploited to deal with the pressure-velocity coupling.Emphasis is put on the influence of the tilt angle on the solution symmetry,flow structure,and heat exchange through the walls.The following parameters and related ranges are considered:Rayleigh number 104≤Ra≤5.105,tilt angle 0°≤φ≤90°,Reynolds number 100≤Re≤1000,Prandtl number Pr=0.72,block height B=0.5,opening width C=0.15,and distance between blocks D=0.5.The results reveal different branches of solutions on varying Re andφ.They also show that the symmetry of the solution regarding the P_(2)axis is retained for all cases with no tilt and for values of Re between 100 and 1000.

Analysis of Cavitation Performance of a 2-D Hydrofoil Based on Mixed-iterative Method

In order to study cavitation characteristics of a 2-D hydrofoil, the method that combines nonlinear cavitation model and mixed-iteration is used to predict and analyze the cavitation performance of hydrofoils. The cavitation elements are nonlinearly disposed based on the Green formula and perturbation potential panel method. At the same time, the method that combines cavity shape for fixed cavity length （CSCL） iteration and cavity shape for fixed cavitation number （CSCN） iteration is used to work out the thickness and length of hydrofoil cavitations. Through analysis of calculation results, it can be concluded that the jump of pressure and velocity potentially exist between cavitation end area and non-cavitations area on suction surface when cavitation occurs on hydrofoil. In certain angles of attack, the cavitation number has a negative impact on the length of cavitations. And under the same angle of attack and cavitation number, the bigger the thickness of the hydrofoil, the shorter the cavitations length.

Study on hysteresis phenomenon in the acceleration phase of supercavitation vehicle

This paper aims to explore cavity shape variation regularity in the acceleration phase of supercavitat- ing vehicle. According to the theory of Homogenous Equilibrium Flow,with Mixture Multiphase Model,by setting up the flow speed at the inlet boundary as a function of time,this study carried out the experiments for the supercavitation vehicle's numeral model and obtained the variation regularity of cavity shape,the viscous drag coefficient and the cavity hysteresis time when the supercavitating vehicle was in the phase of acceleration. Results show that when the vehicle is in the phase of acceleration,at the same cavitation number,the cavity size decrease with the increase of acceleration. With the decrease of cavity number,the effect of acceleration on cavity shape is smaller,but the viscous drag increases along with the increase of acceleration. On the condition when the velocity reaches equality uniform status,the cavity hysteresis decreases as the acceleration becomes smaller. On the condition of the same acceleration,the cavity hysteresis time decreases as the velocity increases.

NUMERICAL SIMULATION OF ARTIFICIAL VENTILATED CAVITY

In order to determine artificial ventilated cavity shape and provide design reference for engineering applications, the shape of ventilated cavity and the drag of underwater body have been numerically simulated with commercial code in this work. Empirical formulas between ventilated cavity shape and cavitation number are obtained under the conditions of zero incidence and similarity shapes of ventilated cavity and vapor cavity have been validated under the same cavitation number. In addition, the relations between change of cavitator incidence and cavity unsymmetry and the relations of between drag and cavity shape have been primarily analysed. Furthermore, the numerical results fit well with the experimental results.

Numerical Analysis on Solidification Behavior of Graphene Nanoplatelet Based Nanofluid in Cold Storage Cavity

Addition of graphene nanoplatelet(GNP)into water is a promising method for improving cold storage system performance,and its application requires comprehensive understanding of solidification behavior of GNP-water nanofluid.In the present study,the influences of GNP mass concentration,cold storage cavity size and shape on solid-liquid interface evolution,temperature distribution,streamline profile as well as solidification rate are numerically analyzed.The enthalpy-porosity technique is adopted to track solid-liquid interface.The results show that the enhancement effect of GNPs on solidification is mainly reflected in the final stage in which heat conduction is predominant;the solidification occurs at the bottom of cavity in the early stage,and the solid-liquid interface is similar to the shape of cavity itself and then tends to be circular in the middle and final stages respectively;the reduction degree of solidification time reaches 30.1%at GNP mass concentration of 1.2 wt%under present simulation conditions;decreasing cavity size and adopting triangular cavity are beneficial for promoting the solidification,but they will suppress the enhancement effect of GNPs on solidification.