ASSESSMENT OF FLOW INTERACTIONS BETWEEN CIRCULAR CYLINDERS AND NACA-0018 HYDROFOILS AT LOW REYNOLDS NUMBERS

Force oscillations and flow around submerged objects at low Reynolds numbers are very important subjects in marine environments. On the other hand, NACA hydrofoils and circular sections are two of the most prevalent shapes that are applied in marine systems and due to the stated reason their hydrodynamic investigation becomes immensely important. Accordingly, in this paper, a flow solver has been developed based on finite volume method, and flow interactions between circular cylinders and NACA-0018 hydrofoils have been considered. For this purpose, different parametric studies have been conducted on the angles of attack and the distance of the foil from the cylinder at three different Reynolds numbers of 100, 200, and 300. Moreover, frequency of the lift and drag coefficients have been analyzed in different cases. As a result, suitable arrangements of the cylinders and foils are determined in the context of an energy conversion system where force fluctuation is helpful and flow around foils and cylinders where fluctuation of forces around them are harmful and vibration or noise propagation should be controlled

ESTIMATION OF WATER ENTRY FORCES, SPRAY PARAMETERS AND SECONDARY IMPACT OF FIXED WIDTH WEDGES AT EXTREME ANGLES USING FINITE ELEMENT BASED FINITE VOLUME AND VOLUME OF FLUID METHODS

In this paper, water entry of wedges with deadrise angles ranging from 10 to 80 degrees at two different velocities is simulated. Impact forces, spray parameters, cavity formation above the chine, and secondary impact forces due to the cavity formation are investigated with particular focus on the extreme angles. To this end, a two dimensional two-phase Finite-Element based Finite-Volume (FEM-FVM) code is developed and validated against experimental data with good compliance. Free surface modeling in this software is accomplished by applying Volume of Fluid (VOF) method. In addition to the extraction of impact forces, secondary impact forces, spray characteristics, and cavity formation, it is demonstrated that there is a combined critical length and entry velocity where the spray formation stops and the spray vanishes. It is also shown that the cavity and secondary impact do not occur under these circumstances. Moreover, it is concluded that for these particular cases, there is a maximum secondary impact force that occurs for the deadrises angles less than 20o

SPS TURBULENT MODELING OF HIGH SPEED TRANSOM STERN FLOW

Transom stern flow is a complicated fluid flow phenomenon especially at high speed regime. Therefore, various authors have studied the transom stern flow, both numerically and experimentally. Smoothed Particle Hydrodynamics method can be considered as a good choice for simulation of nonlinear physics related to the transom flow. Accordingly, SPH as a meshless, Lagrangian, and particle method is presented in this article and SPS turbulent model is also included for more accurate solution. For density modification, a second order density filter scheme is employed. For validation of numerical setup, several draft based Froude numbers are considered and it is shown that SPH solution is in good agreement with available experimental data. Furthermore, three longitudinal Froude number are investigated for high speed transom flow simulation. High speed cases are compared with Savitsky’s formula and it is observed that at high speeds, SPH solutions are also reasonable

Power Matrix of Spherical and Conical Wavestar Geometry with Linear and Circular Arrangement

This article investigated two different arrays of Wavestar wave energy converter (WEC) with two spherical and conical WEC geometry. The boundary element method and radiation/diffraction theory have been used to evaluate the absorbed power of the Wavestar WECs under different wave heights and periods. For validation of numerical analysis, the heave position and velocity for with and without damping coefficient compare with experimental data. Single Wavestar with spherical and conical geometry under different wave periods were investigated and then two linear and circular arrays for both considering geometries compared with each other. The result shows better performance of a circular array than a linear array for all WECs. Absorbed power by the conical geometry is bigger than the spherical geometry. Besides, the maximum power is belonging to the wave period of 6s and 7s for a circular array while in a linear array the maximum power shift to wave periods of 7s and 8s

LARGE EDDY SIMULATION OF ULTRA-HIGH INJECTION PRESSURE DIESEL SPRAY IN MARINE DIESEL ENGINES

Large Eddy Simulation (LES) scheme and a new modified breakup model have been implemented in the OpenFOAM freeware for simulating ultra-high injection pressure diesel and Marine Diesel Fuel (MDF) sprays. Also, the dynamic of dispersed droplet has been modelled by the Lagrangian Particle Tracking (LPT) scheme. The proposed LES/LPT method has been validated by matching it against published experimental data and numerical results of Fluent software under different injection pressures of up to 300 MPa. Furthermore, comparisons have been drawn with Reynolds Averaged Navier-Stokes (RANS) simulations. Spray shape and geometry, droplet penetration and size as well as equivalent ratio are compared with experimental data. Based on the obtained numerical results, main spray characteristics have been simulated accurately by LES and RANS, but the LES results display greater precision in transient conditions. Later, numerical sensitivity of the LES results to the mesh resolution is discussed. Finally, it is found that the proposed LPT/LES scheme along with the advanced breakup model gives more accurate results than the conventional RANS model under ultra-high injection pressures. This advanced scheme has been implemented to investigate the influence of Marine Fuel on spray characteristics

PROBING INTO THE EFFECTS OF CAVITATION ON HYDRODYNAMIC CHARACTERISTICS OF SURFACE PIERCING PROPELLERS THROUGH NUMERICAL MODELING OF OBLIQUE WATER ENTRY OF A THIN WEDGE

The current paper investigates flow around a blade section of a surface piercing hydrofoil. To this end, a thin wedge section is numerically modelled through an oblique water entry. The flow is numerically studied using a multiphase approach. The proposed numerical approach is validated in two steps. First, pressure and free surface around a wedge entering water are simulated and compared against previously published analytical results. Subsequently, cavitation phenomenon around a submerged supercavitating hydrofoil is modelled and analyzed. It is observed that cavity length, pressure, and lift force are accurately predicted. Subsequently, the main problem has been studied for two different cavitation numbers for a range of advanced ratios equivalent to fully, transition and partially ventilated conditions in order to investigate the effect of ambient pressure on hydrodynamics of the water entry of the foil. The numerical findings reveal that, when the cavitation number decreases, the start of transition mode is postponed and this mode is expanded for the larger range of velocity ratios. This implies that fully ventilated velocity ratio modes are expanded, too. However, in the transition mode, the cavitation number plays an essential role and may lead to a decrease in the pressure difference across the surface piercing hydrofoil which yields a decrease in the resultant force