scholarly journals Numerical simulations of flow past an autonomous underwater vehicle at various drift angles

2012 ◽  
Vol 9 (2) ◽  
pp. 135-152 ◽  
Author(s):  
Sreekar Gomatam ◽  
S Vengadesan ◽  
S K Bhattacharyya
Keyword(s):  
Autonomous Underwater Vehicle ◽  
Three Dimensional ◽  
Symmetry Plane ◽  
Underwater Vehicle ◽  
Navier Stokes ◽  
Structure Variation ◽  
Flow Past ◽  
Computational Fluid Dynamics Cfd ◽  
Marine Engineering ◽  
Flow Variables

Three dimensional (3D) flow past an Autonomous Underwater Vehicle (AUV) is simulated using a Computational Fluid Dynamics (CFD) approach at a Reynolds (Re) number of 2.09x106. A non-linear k-? (NLKE) turbulence model is used for solving the Reynolds Averaged Navier-Stokes (RANS) equations. The effect of control surfaces over the flow, the flow interaction between the hull and the appendages at various Angles of Attack (AoA) and the effect of the symmetry plane is studied. Flow structure, variation of flow variables and force distribution for various AoA are presented and discussed in detail.DOI: http://dx.doi.org/10.3329/jname.v9i2.12567 Journal of Naval Architecture and Marine Engineering 9(2012) 135-152

Analysis of Hydrodynamic Characteristics in the Process of Autonomous Underwater Vehicle Docking

2015 ◽  
Author(s):  
Xiaoxu Du ◽  
Huan Wang
Keyword(s):  
Drag Coefficient ◽  
Autonomous Underwater Vehicle ◽  
Simple Algorithm ◽  
Underwater Vehicle ◽  
Navier Stokes ◽  
Hydrodynamic Characteristics ◽  
Successful Operation ◽  
Underwater Docking ◽  
Computational Fluid Dynamics Cfd ◽  
Volume Method

The successful operation of an Autonomous Underwater Vehicle (AUV) requires the capability to return to a dock. A number of underwater docking technologies have been proposed and tested in the past. The docking allows the AUV to recharge its batteries, download data and upload new instructions, which is helpful to improve the working time and efficiency. During the underwater docking process, unsteady hydrodynamic interference occurs between the docking device and an AUV. To ensure a successful docking, it is very important that the underwater docking hydrodynamics of AUV is understood. In this paper, numerical simulations based on the computational fluid dynamics (CFD) solutions were carried out for a 1.85m long AUV with maximum 0.2 m in diameter during the docking process. The two-dimensional AUV model without fin and rudder was used in the simulation. The mathematical model based on the Reynolds-averaged Navier-Stokes (RANS) equations was established. The finite volume method (FVM) and the dynamic structured mesh technique were used. SIMPLE algorithm and the k-ε turbulence model in the Descartes coordinates were also adopted. The hydrodynamics characteristics of different docking states were analyzed, such as the different docking velocity, the docking device including baffle or not. The drag coefficients of AUV in the process of docking were computed for various docking conditions, i.e., the AUV moving into the docking in the speed of 1m/s, 2m/s, 5m/s. The results indicate that the drag coefficient increases slowly in the process of AUV getting close to the docking device. When the AUV moves into the docking device, the drag coefficient increases rapidly. Then the drag coefficient decreases rapidly. The drag coefficient decreases with the increase of velocity when AUV enters the docking device. It was also found that the drag coefficient can be effectively reduced by dislodging the baffle of docking device.

scholarly journals Optimal design of nose and tail of an autonomous underwater vehicle hull to reduce drag force using numerical simulation

2019 ◽  
Vol 234 (1) ◽  
pp. 76-88 ◽  
Author(s):  
Mohammad Saghafi ◽  
Roham Lavimi
Keyword(s):  
Energy Consumption ◽  
Drag Force ◽  
Autonomous Underwater Vehicle ◽  
Turbulence Modeling ◽  
Stokes Equations ◽  
Autonomous Underwater Vehicles ◽  
Three Dimensional ◽  
Underwater Vehicle ◽  
Underwater Vehicles ◽  
Navier Stokes

In this research, the flow around the autonomous underwater vehicles with symmetrical bodies is numerically investigated. Increasing the drag force in autonomous underwater vehicles increases the energy consumption and decreases the duration of underwater exploration and operations. Therefore, the main objective of this research is to decrease drag force with the change in geometry to reduce energy consumption. In this study, the decreasing or increasing trends of the drag force of axisymmetric bare hulls have been studied by making alterations in the curve equations and creating the optimal geometric shapes in terms of hydrodynamics for the noses and tails of autonomous underwater vehicles. The incompressible, three-dimensional, and steady Navier–Stokes equations have been used to simulate the flow. Also, k-ε Realizable with enhanced wall treatment was used for turbulence modeling. Validation results were acceptable with respect to the 3.6% and 1.4% difference with numerical and experimental results. The results showed that all the autonomous underwater vehicle hulls designed in this study, at an attack angle of 0°, had a lower drag force than the autonomous underwater vehicle hull used for validation except geometry no. 1. In addition, nose no. 3 has been selected as the best nose according to the lowest value of stagnation pressure, and also tail no. 3 has been chosen as the best tail due to the production of the lowest vortex. Therefore, geometry no. 5 has been designed using nose and tail no. 3. The comparison made here showed that the maximum drag reduction in geometry no. 5 was equal to 26%, and therefore, it has been selected as the best bare hull in terms of hydrodynamics.

Mechanism and Flow Control on the Mismatching of Impeller and Vaned Diffuser Caused by Inlet Prewhirl for Centrifugal Compressors

2016 ◽  
Author(s):  
Qiangqiang Huang ◽  
Xinqian Zheng ◽  
Aolin Wang
Keyword(s):  
Flow Control ◽  
Control Method ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Vaned Diffuser ◽  
Inlet Distortion ◽  
Computational Fluid Dynamics Cfd ◽  
Stagger Angle ◽  
Good Agreement ◽  
Matching Relation

Air often flows into compressors with inlet prewhirl, because it will obtain a circumferential component of velocity via inlet distortion or swirl generators such as inlet guide vanes. A lot of research has shown that inlet prewhirl does influence the characteristics of components, but the change of the matching relation between the components caused by inlet prewhirl is still unclear. This paper investigates the influence of inlet prewhirl on the matching of the impeller and the diffuser and proposes a flow control method to cure mismatching. The approach combines steady three-dimensional Reynolds-averaged Navier-Stokes (RANS) simulations with theoretical analysis and modeling. The result shows that a compressor whose impeller and diffuser match well at zero prewhirl will go to mismatching at non-zero prewhirl. The diffuser throat gets too large to match the impeller at positive prewhirl and gets too small for matching at negative prewhirl. The choking mass flow of the impeller is more sensitive to inlet prewhirl than that of the diffuser, which is the main reason for the mismatching. To cure the mismatching via adjusting the diffuser vanes stagger angle, a one-dimensional method based on incidence matching has been proposed to yield a control schedule for adjusting the diffuser. The optimal stagger angle predicted by analytical method has good agreement with that predicted by computational fluid dynamics (CFD). The compressor is able to operate efficiently in a much broader flow range with the control schedule. The flow range, where the efficiency is above 80%, of the datum compressor and the compressor only employing inlet prewhirl and no control are just 25.3% and 31.8%, respectively. For the compressor following the control schedule, the flow range is improved up to 46.5%. This paper also provides the perspective of components matching to think about inlet distortion.

scholarly journals Three-Dimensional Navier–Stokes Analysis and Redesign of an Imbedded Bellmouth Nozzle in a Turbine Cascade Inlet Section

1996 ◽  
Vol 118 (3) ◽  
pp. 529-535 ◽  
Author(s):  
P. W. Giel ◽  
J. R. Sirbaugh ◽  
I. Lopez ◽  
G. J. Van Fossen
Keyword(s):  
Three Dimensional ◽  
Navier Stokes ◽  
Experimental Measurements ◽  
Inlet Section ◽  
Turbine Cascade ◽  
Blade Cascade ◽  
Inlet Geometry ◽  
Computational Fluid Dynamics Cfd ◽  
Transonic Turbine ◽  
Flow Nonuniformity

Experimental measurements in the inlet of a transonic turbine blade cascade showed unacceptable pitchwise flow nonuniformity. A three-dimensional, Navier–Stokes computational fluid dynamics (CFD) analysis of the imbedded bellmouth inlet in the facility was performed to identify and eliminate the source of the flow nonuniformity. The blockage and acceleration effects of the blades were accounted for by specifying a periodic static pressure exit condition interpolated from a separate three-dimensional Navier–Stokes CFD solution of flow around a single blade in an infinite cascade. Calculations of the original inlet geometry showed total pressure loss regions consistent in strength and location to experimental measurements. The results indicate that the distortions were caused by a pair of streamwise vortices that originated as a result of the interaction of the flow with the imbedded bellmouth. Computations were performed for an inlet geometry that eliminated the imbedded bellmouth by bridging the region between it and the upstream wall. This analysis indicated that eliminating the imbedded bellmouth nozzle also eliminates the pair of vortices, resulting in a flow with much greater pitchwise uniformity. Measurements taken with an installed redesigned inlet verify that the flow nonuniformity has indeed been eliminated.

Turbine Airfoil Heat Transfer Predictions Using CFD

2005 ◽  
Author(s):  
Anil K. Tolpadi ◽  
James A. Tallman ◽  
Lamyaa El-Gabry
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulence Modeling ◽  
Three Dimensional ◽  
Numerical Approach ◽  
Navier Stokes ◽  
Design System ◽  
Computational Fluid Dynamics Cfd ◽  
Turbine Airfoils ◽  
Typical Design

Conventional heat transfer design methods for turbine airfoils use 2-D boundary layer codes (BLC) combined with empiricism. While such methods may be applicable in the mid span of an airfoil, they would not be very accurate near the end-walls and airfoil tip where the flow is very three-dimensional (3-D) and complex. In order to obtain accurate heat transfer predictions along the entire span of a turbine airfoil, 3-D computational fluid dynamics (CFD) must be used. This paper describes the development of a CFD based design system to make heat transfer predictions. A 3-D, compressible, Reynolds-averaged Navier-Stokes CFD solver with k-ω turbulence modeling was used. A wall integration approach was used for boundary layer prediction. First, the numerical approach was validated against a series of fundamental airfoil cases with available data. The comparisons were very favorable. Subsequently, it was applied to a real engine airfoil at typical design conditions. A discussion of the features of the airfoil heat transfer distribution is included.

Numerical Investigation of the Effect of Balancing-Hole on the Axial Force of a Partial Emission Pump

2014 ◽  
Author(s):  
Zhang Lisheng ◽  
Jiang Jin ◽  
Xiao Zhihuai ◽  
Li Yanhui
Keyword(s):  
Axial Force ◽  
Stokes Equations ◽  
Dominant Role ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Design Parameters ◽  
Navier Stokes Equations ◽  
Computational Fluid Dynamics Cfd ◽  
The Cost

In this paper numerical simulations were conducted to analyze the effects of design parameters and distribution of balancing-hole on the axial-force of a partial emission pump. The studied pump is a single stage pump with a Barske style impeller. Based on the original impeller, we designed 7 pumps with different balancing-hole diameters and the partial emission pump equipped with different impellers were simulated employing the commercial computational fluid dynamics (CFD) software Fluent 12.1 to solve the Navier-Stokes equations for three-dimensional steady flow. A sensitivity analysis of the numerical model was performed with the purpose of balancing the contradiction of numerical accuracy and the cost of calculation. The results showed that, with increasing of the capacity, the axial force varies little. The diameter of the inner balancing-hole plays a dominant role of reducing axial-force of partial emission pump, the axial-force decreases with increasing of inner balancing-hole diameter on the whole range of operation, the axial-force of impeller without inner balancing-hole is approximately 3 times larger than that of impeller with inner balancing-hole. While the diameter of outer balancing-hole has a reverse effects compared with that of inner balancing-hole. With increasing of outer balancing-hole, the axial force increases accordingly.

scholarly journals Feasible Concept of an Air-Driven Fan with a Tip Turbine for a High-Bypass Propulsion System

Energies ◽  
2018 ◽  
Vol 11 (12) ◽  
pp. 3350 ◽  
Author(s):  
Guoping Huang ◽  
Xin Xiang ◽  
Chen Xia ◽  
Weiyu Lu ◽  
Lei Li
Keyword(s):  
Fluid Dynamics ◽  
Carbon Dioxide Emissions ◽  
Three Dimensional ◽  
Propulsion System ◽  
Navier Stokes ◽  
Three Dimensional Flow ◽  
Low Pressure Turbine ◽  
Computational Fluid Dynamics Cfd ◽  
Cfd Method ◽  
Bypass Ratio

The reduction in specific fuel consumption (SFC) is crucial for small/mid-size cost-controllable aircraft, which is very conducive to reducing cost and carbon dioxide emissions. To decrease the SFC, increasing the bypass ratio (BPR) is an important way. Conventional high-BPR engines have several limitations, especially the conflicting spool-speed requirements of a fan and a low-pressure turbine. This research proposes an air-driven fan with a tip turbine (ADFTT) as a potential device for a high-bypass propulsion system. Moreover, a possible application of this ADFTT is introduced. Thermodynamic analysis results show that an ADFTT can improve thrust from a prototype turbofan. As a demonstration, we selected a typical small-thrust turbofan as the prototype and applied the ADFTT concept to improve this model. Three-dimensional flow fields were numerically simulated through a Reynolds averaged Navier-Stokes (RANS)-based computational fluid dynamics (CFD) method. The performance of this ADFTT has the possibility of amplifying the BPR more than four times and increasing the thrust by approximately 84% in comparison with the prototype turbofan.

scholarly journals ICCM2015: A Comparison of RANS and LES Computational Methods in Analyzing Ventilation Flow Through a Room Fitted with a Two-Sided Windcatcher

2017 ◽  
Vol 14 (03) ◽  
pp. 1750021 ◽  
Author(s):  
A. Niktash ◽  
B. P. Huynh
Keyword(s):  
Natural Ventilation ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Interior Space ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Computational Fluid Dynamics Cfd ◽  
Flow Through ◽  
Cfd Method ◽  
Good Agreement

A windcatcher is a structure for providing natural ventilation using wind power; it is usually fitted on the roof of a building to exhaust the inside stale air to the outside and supplies the outside fresh air into the building interior space working by pressure difference between outside and inside of the building. In this paper, the behavior of free wind flow through a three-dimensional room fitted with a centered position two-canal bottom shape windcatcher model is investigated numerically, using a commercial computational fluid dynamics (CFD) software package and LES (Large Eddy Simulation) CFD method. The results have been compared with the obtained results for the same model but using RANS (Reynolds Averaged Navier–Stokes) CFD method. The model with its surrounded space has been considered in both method. It is found that the achieved results for the model from LES method are in good agreement with RANS method’s results for the same model.

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