mojtaba dehghan manshadi

One of the most important issues in designing a submarine is calculating its resistance and power. It is still a scientific challenge to calculate and generalize the results from a scaled model to the main vessel. In this study, the effect of the scale in a numerical method on the resistance coefficients of a submarine, including the total, friction and pressure resistance coefficients, has been investigated by numerical simulation method. Also, the accuracy of the results of the existing empirical relationships for calculating submarine resistance coefficients has been evaluated. The SUBOFF submarine model was used to conduct studies. The results show that the existing empirical relationships enable the calculation of the friction coefficient with an error of less than 10%, the pressure coefficient with an error of less than 30%, and the total drag coefficient with an error of less than 8.5%.

Investigating the effects of free surface on submarine motion near the free surface of water is important. In the present study, the simulation of a submarine near the free surface of water in irregular waves was carried out. To simulate submarine motion, Suboff geometry with appendages was used. For simulating, URANS method with overset grid approach, k-ε realizable turbulence model and vof in Star CCM+ software were used. The validation , uncertainty and accuracy of the results were implemented. Since the freedom of submarine motions may have significant effect on the results of the drag force, the simulations were performed with considering the three motions of heave, pitch, and roll. Differrent simulations were carried out with different wave heights and wave directions. The results showed that increasing the pitch amplitude due to increasing the wave height ,causes to increase the drag force. For significant wave height of 0.43 meters, the maximum drag force in head and beam sea were 444N and 322N respectively.

In this paper, the Smoothed Particle Hydrodynamics (SPH) method with dynamic boundary condition has been used to simulate 3D Fluid flow in the centrifugal pump. Severe fluctuations in the field of pressure and velocity is one of the major problems in this method. In this paper, the fluctuations have been corrected using Delta and Shift algorithms. The simulation was numerically performed with real fluid viscosity (laminar and turbulence). Validation of this method indicated that in the case of real fluid viscosity, the Delta and Shift algorithms should be used simultaneously to obtain good agreement with the experimental data. To validate the pump results, a comparison was made between the numerical outputs and the performance curves of pump EN 125-315 of Pumpiran Company under relatively similar conditions. The results of this comparison showed that the error of simulation of pump head, consumption power and efficiency values compared with experimental data were about 12, 5.5 and 16 percent, respectively.

Two new higher order version of WENO schemes are introduces and problems are solved to investigate problems containing shocks and disturbances in compressible flow. The solver is capable of solving conservation laws using WENO scheme of up to 7th order. The scheme is a recently developed version of the WENO-η-z method with a modified Global Smoothness Indicator (GSI) of 12th order of accuracy, aimed to decrease numerical dissipation over critical points. The code is primarily investigated trough solving several 1D and 2D problems, including the Sod’s shock tub, Lax’s problem, the Shu-Osher problem, which some are presented here as verification. The 2-D shock-bobble interaction and Richtmyer-Meshkov instability are solved as problems including shocks and disturbances, in which proposed methods are compared with both original WENO- η-z and two similarly modified methodes from recent literature. In these problems, the introduced scheme shows lower dissipation in comparison with the original versions, while having more acceptable stability and symmetry against other modifien versions.

Pump jet is a type of marine propulsion system that establishes the necessary trust based on the momentum difference method and based on axial flow pumps. The pump jet system is composed of rotors, stators, ducts and hubs. In the last two decades, pump jet propulsion system due to higher efficiency and performance, as well as lower noise level, has been more important for marine industry, especially in the subsurface area. In this paper, the effect of stator hydrofoil chords length on the hydrodynamic performance of the stator-rotor pump jet has been investigated. The stator has an integral role in this type of pump jet and has a significant role on the hydrodynamic performance of the propulsion complex. Therefore, 5 geometries with the length of the stator cords L (DR 0.14, 0.15DR, 0.16DR, 0.17DR and 0.18DR) (rotor diameter: DR) were produced by direct design method to investigate computational fluid dynamics and numerical simulation using commercial software. Among the investigated cases, the maximum open water efficiency (64.51) was related to L=0.18 DR and the minimum open water efficiency was related to L=0.15 DR (63.53). By examining the other results of the simulations, it seems that L=0.18DR is superior to other scenarios due to having maximum open water efficiency (about 1% higher than the lowest value) and the larger coverage area of the leading coefficients with higher efficiency, uniformity and monotrend of the production trust coefficient and conventional torque coefficient graph.

In this research, authors attempt to investigate the significant and influential characteristics behaviors of the conical nose in supersonic flow as well as discussing the results of using Multi-Row disks and their effects to recognize the behavior of this nose. A cone nose produces low drag and high aerodynamic heat due to sharp tip in flight conditions, which makes it problematic at high speed Mach numbers. Thus, new modifications with the utility of adding Multi-Row disks in the design of this cone nose allows the nose to efficiently reduce the produced aerodynamic heat as well as preserving its nature to produce low drag. Results show that the using 12 disks led approximately 30% reduction in drag coefficient rather than reference nose without disks. It also significantly reduces the static temperature produced on the nose surface. Therefore, this type of nose improves its aerodynamic characteristics that can advise to be used at high speed and raises the possibility of reusing this kind of nose instead of the strict conical one.

In this paper, the Smoothed Particle Hydrodynamics (SPH) method with dynamic boundary condition has been used to simulate 2D floating of objects. Severe fluctuations in the field of pressure and velocity is one of the major problems in this method. In this paper, the fluctuations have been corrected using Delta and Shift algorithms. The simulation was numerically performed with three viscosity models including real fluid viscosity (laminar and turbulence), ideal fluid (without viscosity) and artificial viscosity. Validation of this method indicated that in the case of artificial viscosity and also ideal fluid, the Delta algorithm should be used and in the case of real fluid viscosity, using Delta and Shift algorithms could establish good agreement with experimental data. Finally, by simulating the floating experiment with the obtained optimal numerical models, the results showed that the optimal method in the case of real fluid viscosity had a better performance in modeling the horizontal, vertical and rotational movements of the floating body than other optimal methods.

Nowadays, fuel cell systems are used in energy systems which caused to saving energy, and a high-efficiency system. Recently, Proton Exchange Membrane Fuel Cell (PEMFC) has been considered for aerospace applications especially in Unmanned Aerial Vehicle (UAV). In the present study, this system has been used for power generation in the different phase of flight, such as takeoff, climb, maximum speed, and cruise. Also, a comprehensive parametric study is carried out to show the effects of some key parameters (including current density, surface area of the fuel cell, takeoff distance, and stoichiometric air ratio) on the main performance criteria of the PEMFC system. The results indicate that the current values for the power required for maximum speed, climb, takeoff, and cruise are 8, 6.576, 5.593, and 2.098, respectively. According to the results, increasing the takeoff distance leads to a reduction in the required power and the system input hydrogen. Also, with increasing current density, power and hydrogen consumption increase, while fuel cell and exergy efficiency decrease.

In the present study, the wake flow field of a submarine model was investigated experimentally in a wind tunnel. The experiments were conducted to determine the effect of the location of control surfaces on the wake inflow to the impeller of the submarine. In order to investigate the effect of the location of control surfaces as the most important innovation of the present study, the aforementioned surfaces were installed in three longitudinal positions X/L=0.89, 0.92, 0.95 on the heel of the submarine model, and the wake flow was measured at position X/L=1.7 and the Reynolds number 6*10^5  by a five-hole probe and a hotwire anemometer. Finally, the longitudinal position X/L=0.95 was selected as the optimal location for the stern planes to improve the wake inflow to the impeller in terms of reducing its total area and the least amount of turbulence and non-uniformity. The results obtained during this study showed that arriving of the holder basechr(chr('39')39chr('39'))s wake to the stern area increases ​​the area and average velocity and subsequently reducing the non-uniformity of the wake flow.

Researchers have recently paid a lot of attention to drag force estimation over different bodies. This force is usually calculated using surface integral over the body and momentum defect method in the wake region. In this research, the steady-state, incompressible drag force calculation around a submarine model is numerically investigated using the latter technique (momentum defect method). Simulations were carried out at different aspect ratios at zero angle of attack and the capabilities of this method at inclined flows were also investigated. The most important parameters which affect the results are the vertex space, the distance of data collection section, and the data collection section size. In this article, practical suggestions are made for each parameter. The contribution of the pressure, momentum, and turbulence term were also evaluated at different cross sections. These findings can be implemented in wind tunnels with small test section length. They can also be used to compare the results with the common CFD surface integral method. By using the results of this research, the maximum error implementing this technique at zero and non-zero angle of attack will be about 4% and 16% respectively.

In the present study, far-field aeroacoustic noise emitted from flow over CAARC tall building model at different angles of attack is investigated. The unsteady surface pressure measurements are conducted in a wind tunnel. The purpose of this study is to estimate the far-field noise emitted by measuring the unsteady surface pressures. The surface pressure data are used as input of a numerical algorithm to solve Fw-H equation. The aerodynamic and aeroacoustic characteristics of flow over a 2D square cylinder and the CAARC model are presented. The results revealed that the peak of vortex shedding frequency could be observed in the spectrum of surface pressure signals of sensors located on the side surfaces of the model. Its frequency is in an excellent agreement with the hot wire measurement results. The Strouhal number for flow around CAARC model changes in the range of 0.08-0.1 depending on the angle of attack. Also dipole pattern for sound radiation was also observed for 3D model which is related to the vortex shedding phenomenon. The effect of angle of attack on the SPL is also dependent to the reciever’s location.

Surface pressure distributions and boundary layer profiles are measured over the nose surface of a submarine model in a wind tunnel. The tests are conducted for two different nose shapes in order to study the effects of nose shape on the flow field around the model. The influence of Reynolds numbers, which are 0.5×106, 0.8×106 and 106, and pitch angles, α = 0, 5, 10 and 15°, on the surface pressure distribution over the surface of two nose shapes are investigated. Furthermore, the effect of the longitudinal pressure gradient on the boundary layer velocity profiles and the probability of the separation in the plane of symmetry of the nose are studied. It is found that the Reynolds number does not have a significant influence on the nose surface pressure distribution at all pitch angles. The results show that the presence of the adverse pressure gradient in major portion of the blunter nose shape causes the non-dimensional velocity profiles of boundary layer in locations of 0.1≤X/L≤0.23 are deviated from the log layer profile. Therefore the separation on the blunter nose shape is more likely than the other nose at high pitch angle manoeuvres.

In the present study, to extend the Stokes' second problem, the bottom edge of viscous incompressible semi-space resting fluid is excited in two dimension, simultaneously. This two-dimensional excitation which is the effect of velocity of two-dimensional travelling wave, is boundary condition for the two-dimensional linear Navier-Stokes equations. The time-space exact solution for fluid velocity and pressure show that the amplitude of oscillating velocity has fast damping in space till 1.87 micron from excited surface. After this height, the amplitude of oscillating quantities has a slowly damping. In the first region (in fast damping region), phase difference between pressure and velocity is changing, but after that there is a region with constant phase difference. The space variation in velocity components of surface wave, together with the coupling of velocity components in main equations, produces pressure wave. It has been found that kinematic effect of vertical and horizontal harmonic motion cause damped rotational motion in fluid.

The vortex generated around a submarine has an important influence on the uniformity of the submarine wake at the propeller and hydrodynamic noise. A suitable way to reduce the effects of this separated flow is to use vortex generators. Vortex generators have different arrangement such as counter-rotating and co-rotating. The main goal of the present study is to investigate the flow field around a standard underwater model employing the vortex generator with different arrangement by using the CFD method (OpenFOAM code) in 0°≤α≤30° angles of attack. In this study, the application of CFD simulation which can help us to precisely study the structure of vortical flow field. The results show that counter-rotating vortex generators placed along the submarine do indeed significantly reduce strength of the vortex, line separation, size of cross-flow vortices and drag force. The amount of the drag reduction for the counter-rotating vortex generator is approximately 14% in α=30° and approximately 21% in β=30°.

One of the most important parts of the polymer fuel cell is the bipolar plate, which through the channel paths as the flow field in these plates, the availability of reactive gases to the surface of the catalyst layer is possible to carry out the electrochemical reactions of the fuel cell. So far, many researchers have been designing different flow streams for fuel cells, although each of the models has its own advantages and disadvantages, but a suitable design for the fuel cell flow field, which has a uniform distribution of reactive gases on the surface of the catalyst layer, Access to higher performance and longer fuel cell life is very important. In this paper, we introduce a new flow pattern for fuel cell flow field, and the numerical results obtained with a conventional parallel model are compared. The flow-shaped designs have been modified with a spiral and the total dimensions of the cell are 6400 mm 2, which has allowed access to uniform distribution of reactive gases, flow density and temperature distribution. An increase of 66% was achieved with a limited density and increased 1.7 times the power density by adjusting the arrangement for the flow field. Therefore, considering the design of the fuel cell based on the power density curve presented in the new model, the specific characteristics and power of the fuel cell in an air mission have been addressed and the availability of high specific power that is of particular importance in aerial applications is achieved.

In the present research aeroacoustic characteristics of flow over a finite height wall mounted square cylinder at different angles of attack is investigated. The aspect ratio of the model and the boundary layer thickness were 7 and δ⁄D=4.27, respectively. The experiments were done in a acoustically improved aerodynamic wind tunnel. The purpose of this study is to identify correlation between the fluid and the acoustic fields. The flow-induced noise was measured using single microphone. The measured noise is related to aerodynamic characteristics of the flow using a single hot wire. The flow-induced noise of the cylinder is characterized in terms of frequency and magnitude. A sharp pick was observed in the far-field pressure at the vortex shedding frequency in which measured with hot wire anemometer. So, one could be concluded that vortex shedding is a source of aerodynamic noise generation. The strouhal number obtained from two devices was almost equal to 0.11 that is in agreement with previous studies. Also, maximum vortex shedding frequency was measured for α=15°. It is observed that sound pressure level is increased with increasing upstream velocity. The overall sound pressure level ranged between 84.2 and 110.95 (dB) for upstream velocities in the range of 5-15 (m/s). The angle of attack has no important effect on overall sound pressure level.

In the present research, numerical simulation of the characteristic chart and steady-state Wakefield flow around a marine propeller is conducted. Solutions were performed using the open-source OpenFOAM software and the steady incompressible simple-Foam solver. The gradients were calculated using the linear Gauss algorithm, and the pressure equation was solved with the multi-grid method. In this research, characteristic chart simulation of the propeller was carried out for the entire operational conditions and the effect of using Realizable-k-ε and k-ε-v^2-f turbulence models on the results was investigated. The results were found to be in good agreement in all conditions except for the near bollard region. In this region, the propeller inlet angle of attack severely increased, and the two equation model predicted the thrust coefficient with 24% error, while implementing the four equation model significantly developed the results and decreased the error to 5%. The wake region parameters were also investigated in the numerical simulations at different longitudinal and radial cross sections behind the propeller which showed good agreement compared with the available experimental data. Wake region investigation showed that the flow behavior in downstream cross sections is similar to the corresponding upstream section with smaller variation ranges and for the swirling flow behind the propeller, the maximum and minimum angular position of the wake components rotates. The obtained results also show that the wake axial velocity component deviation is extremely large at the blade tip.

In the present study, wake structure downstream a 3D square cylinder is experimentally investigated. The contours of mean velocity, total pressure, static pressure and vorticity are presented for the wake region. Five-hole probe is used for extracting the required wake properties and determining the flow structure. A novel neural network method is used for calibrating the five hole prob. The calibration map obtained by this method is compared with the conventional linear and 5th order polynomial surface fit algorithms. Based on the statistical parameters of calibration data, it is shown the neural network algorithm is more accurate and works faster than the other methods. Experimental results showed that with increasing the distance from the cylinder, tip and base vortices are weakened, the height of wake region decreases while its width increases simultaneously. The effects of free end shear layer on the flow structure are clarified in the results. Downwash flow from free end of cylinder and upwash flow from the bottom wall decrease the width of the wake region near top and bottom of cylinder in comparison with the mid-height region. The effect of free end shape of a finite square cylinder is also investigated. The shear layer separated from the free end plays an important role.

This work aims to prediction of laminar/turbulent transition which plays an important role on aerodynamics of wing section. In this respect the flow around the NACA2415 airfoil simulated in a Computational Fluid Dynamics (CFD) solver in different regimes with and without propeller flowfield. For predicting the transition onset, two approaches were used: The first is based on time history of the skin-friction coefficient for determining the transition onset and the transition length on the airfoil. The second is to apply transition γ-〖Re〗_θ model for laminar/turbulent transition simulation. For investigation of transition effect, the simulation repeated by use of a classical turbulent model and both results was compared with experimental data. The comparison shows that taking into account the transition effects gives a good agreement with experiment. Relative error of calculated drag coefficients for the transition based simulation is lower than 10%, while fully turbulent simulation are 70% overestimated in some incidences. Slipstream of upstream propeller changes flow pattern and boundary layer characteristics over the wing. Indeed in presence of propeller, spanwise load distribution and laminar/turbulent transition onset were affected. In propeller flowfield, increasing of velocity normal component over wing surface causes transition delay. Movement of transition onset to trailing edge on the upper surface in propeller downwash is representative of such phenomenon. On the other hand, in upwash region, the transition onset moves upstream. With the increasing propeller rotational speed, this tendency augments and so the transition onset on the wing upper surface moves far downstream in propeller downwash.

The horseshoe vortex generated around the sail-body junction of a submarine has an important influence on the uniformity of the submarine wake at the propeller and hydrodynamic noise. The influence of the horseshoe vorex on the submarine performance is not negligible. A suitable way to reduce the effects of this separated flow is to use vortex generators. The main goal of the present study is to investigate the flow field around a standard underwater model employing the vortex generator by using the oil flow visualization method and CFD method (OpenFOAM code) in 0°≤α≤30° angles of attack. In this study, the application of experimental method in wind tunnel and CFD simulation which can help us to precisely study the structure of vortical flow field. The results show that Vortex Generators placed along the submarine do indeed significantly reduce strength of the horseshoe vortex, line separation, size of cross-flow vortices and drag force.

The effect of sail position on the downstream flow field of the sail is investigated in the wind tunnel. A five-hole pressure probe is used to measure the 3D flow field. The investigation of the five-hole results shows that the five-hole measurements can determine the horseshoe vortex structure. Also, the results show that the horseshoe vortexes become smaller by forward moving of the sail on the body to the nose. Therefore, if the sail is mounted on the hull near the bow, the performance of the impeller increases and nose level decreases.

In this study, the vertical flow on a sharp edged, 70 degrees swept back delta wing was experimentally investigated in a smoke tunnel, using laser sheet technique. Previous studies show that changing Reynolds number has little effect on the vortex structure of sharp edged delta wings, although the angle of attack has the major effect. Furthermore, Spalart Almaras model is used for numerical investigation on the delta wing. The effect of angle of attack on size and break-down location of the vortices on the wing was studied. The results show that increasing of the angle of attack increases the size of the vortices and the height of the vortex core to the wing surface as well. The bigger vortex on a delta wing leads to increasing the lift of the wing and it increases the maneuverability of the aircraft. Abrupt changes occur in the structure of the vortices at very high angles of attack which is designated as vortex break-down. The vortex break-down cause’s intense oscillation of the surface pressure of the wing and it decreases the aircraft maneuverability.

In present study, the wake flow field of a submarine model was investigated experimentally in a wind tunnel. These experiments were conducted in four different locations X/L= 0.85, 1, 1.25 and 1.5 downstream of the model at Reynolds number of 3.85×105 by a five hole probe. The effect of various factors such as the variation of Reynolds number, the installation of the trip strip on the model nose surface, the mounting of the appendages on the submarine bare hull model and the nose shape effect on the wake structure were investigated in this study. The results showed that the installation of the trip strip on the nose surface did not have recognizable effects. By Increasing the Reynolds number, the amount of the dropping velocity in the wake field decreased due to the decreasing of the separation region on the after-body section. Presentation of the appendages on the model surface lead to the increasing of the wake area. The effect of the nose shape on the wake of the submarine model is the main innovation in the present work. Investigations showed that the velocity in the central part of the wake for non-axisymmetric nose shape (TANGO) decreased in comparison with the axisymmetric nose shape (SUBOFF and STANDARD).

The fThe flow field around the axisymmtric stream lined bodis which forms the main body of the airplaines and submarines has been the subject of several researches. Turning maneuvers of submarines result in cross flow separation that generates large hydrodynamic forces. The separation of a simple axisymmetric body is very complex in nature. Understanding these vortical flows is paramount to improving vehicle performance and design. A suitable way to reduce the effects of this separated flow is to use vortex generators. The main goal of the present study is to investigate the flow field around a Suboff standard underwater model employing the vortex generator by using the oil flow visualization method and CFD method (OpenFOAM code) at 0° ≤ α ≤ 30° angles of attack. The novelty of the this study is the application of oil flow visualizing method and CFD simulation which can help us to precisely study the structure of three-dimensional vortical flow field. The results show that Vortex Generators placed along the submarine do indeed significantly reduce cross flow separation, size of vortices and drag forces.

This study focuses on transition of laminar to turbulent flow around a symmetrical airfoil at a low Reynolds number in free flow and flow near the ground at different angles of attack. Finite volume method is adopted to solve the unsteady Reynolds-averaged Navier–Stokes (RANS) equation. Flow around the symmetrical airfoil SD8020 at a low Reynolds number (4000) at 5 and 8 degree angle attack has been simulated in free stream and near the groundnumerically. Current numerical result is compared with other’s experiment and numerical result in free flow at low Reynolds number and flow in ground effect that good agreement has been obtained in aerodynamic coefficient prediction. SIMPLEC method is used for pressure and velocity coupling and flow equations discrete with Quick method. Transition-SST model is used for modeling turbulence of flow. Result shows that the current numerical method can detect adverse pressure gradient، laminar separation bubble and transition of laminar flow to turbulent. According to the result، in ground effect location of laminar separation bubble، length of bubble and location of transition is moved to leading edge and pressure distribution is effected by location of laminar separation bubble.