Numerical Simulation of the Overall Flow Field for Underwater Vehicle with Pump Jet Thruster

Transcription

1 Available online a Procedia Engineering 31 (2012) Inernaional Conference on Advances in Compuaional Modeling and Simulaion Numerical Simulaion of he Overall Flow Field for Underwaer Vehicle wih Pump Je Thruser Yongxiang Dong *, Xiangie Duan, Shunshan Feng, Zhiyu Shao Sae Key Laboraory of Explosion Science and Technology, Beiing Insiue of Technology, Beiing , China Absrac The flow field numerical simulaion of underwaer vehicle wih pump e hruser was performed using he commercially available CFD sofware FLUENT based on he Reynolds averaged Navier Sokes Equaions and k- epsilon RNG urbulence model. Muliple reference frames (MRF) was used o associae he inerior flow field of he pump e hruser and exerior flow field of he underwaer vehicle. Validiy of he CFD model is verified using daa from experimen. Characerisic of he overall flow field was obained and pressure disribuion of he propulsion was also given. The simulaion resuls could be regarded as an imporan reference in he opimal design of pump e hruser and he hydrodynamic characerisics of underwaer vehicle Published by Elsevier Ld. Selecion and/or peer-review under responsibiliy of Kunming Universiy of Science and Technology Open access under CC BY-NC-ND license. Keywords: Pump e hruser; Flow field wih power; Hhydrodynamic characerisics; MRF 1. Inroducion Pump e hrusers have been widely used as a propulsion device in underwaer vehicle because of heir excellen low noise characerisics [1]. The srucural diagram of he underwaer vehicle wih pump e hruser was showed in Fig 1. The pump e hruser componens include a roor which roaes o obain hrus, a saor prevens he roaion movemen o offse he imbalance orque and a duc which proecs he roor and saor. The complicaed srucure of propulsion conribues o he complicaed flow characerisics. * Corresponding auhor. Tel.: ; address: dongyongx@bi.edu.cn Published by Elsevier Ld. doi: /.proeng Open access under CC BY-NC-ND license.

2 770 Yongxiang Dong e al. / Procedia Engineering 31 (2012) Meanwhile, he wake flow field performance of underwaer vehicle is affeced by he pump e hruser significanly. I resuls ha hydrodynamic characerisics will be affeced ineviably. Thus, research on overall flow field of underwaer vehicle acceleraed by pump e hruser is of grea significance. A few of he researchers has conduced he sudy of he inerior flow field of pump e hruser, as in [2][3]. Bu hey focus on only inerior flow field, few can provide he characerisics of he overall flow field includes boh inerior flow field and exerior flow field of he underwaer vehicle, which is usually he mos imporan o analyze he propulsion performance and is influence on he hydrodynamic characerisics of he underwaer vehicle. Fig. 1. Underwaer vehicle acceleraed by he pump e hruser In his paper, he muliple reference frames (MRF) is applied o associae he exerior flow field of underwaer vehicle wih he inerior flow field of propulsion. Hybrid grid is used because of he srucural complexiy. The Fluen sofware is used o solve he RNAS equaions wih RNG k- urbulence model. The overall flow field of under vehicle wih pump e hruser is simulaed.comparison of he simulaion resuls wih a previously conduced full scale model experimen is performed, and he flow characerisic and he pressure disribuion on he overall flow field wih propulsion are given a las. 2. Flow Simulaion Model of he Overall Flow 2.1. Physical Model and Mesh Generaion In a flow field simulaion, compuaional domain selecion is a key facor which deermines he complexiy and successfulness of he problem [4]. In our work, we are mainly concern how he flow in he inerior of propulsion ineracs wih he exerior flow field of he underwaer vehicle and is influence on hydrodynamic characerisics, so waer in he inerior of propulsion as well as ouside of he underwaer vehicle are boh included in he compuaional domain. Due o he dissymmery of he propulsion, 3D model mus be used in he compuaion. Schemaic and boundary condiions of he longiudinal profile of he physical model is shown in Fig 2. Diameer of he underwaer vehicle (referenced by d) was aken as a reference of he range of he flow field domain. Coordinae origin akes places a he verex of he underwaer vehicle head. The inle, oule, and wall boundary have an offse of 15d, 35d and 15d respecively from he origin. For he underwaer vehicle, he fins and rudders were no modeled for he simpliciy of he problem. To compare he hydrodynamic characerisics of wih and wihou propulsion, he compuaional model wih propulsion (referenced by B+P) and wihou propulsion (referenced by B) were respecively esablished. The mesh generaor used in his work is ICEM CFD. The compuaional domain was spli ino inerior flow field and exerior flow field wich were showed in differen color in Fig.2. For he srucure complexiy of he inerior flow field, unsrucured mesh was used. For he number of grids reducion and

3 Yongxiang Dong e al. / Procedia Engineering 31 (2012) accuracy of he calculaion, high qualiy srucured mesh was used on he exerior flow field. The unsrucured mesh and srucured mesh have he same nodes a he inerface so as o exchange he calculaion informaion Mahemaical model Fig. 2. Schemaic and boundary condiions of he longiudinal profile of he physical model Reynolds averaged Navier Sokes Equaions was used o govern he ranspor of he averaged flow quaniies in consideraion of he reducion of compuaional resources. The equaions which been wrien in Caresian ensor form is: U 0 x u uu P u u 2 u i i i i [ ( ) ] ( uu ) x x x x x i i i 3 x x i Where is he densiy and P is he Reynolds-averaged pressure, U i, and u i, is he fluid mean and flucuaing velociy componens, is he dynamic viscosiy. As i is well known he Reynolds sress ensor uu i needs a closure and a popular one is based on he assumpion of proporionaliy o he srain rae ensor, hrough a urbulen viscosiy v defined as v C 2 k k is he urbulen kineic energy and is he urbulen kineic energy dissipaion rae. In he presen invesigaion he sandard k- model was used and wo addiional equaions were inroduced: k 1 k U Pk (4) x x k x 2 1 U C1 Pk C2 x x x k k (5) Where he urbulen kineic energy producion erm P k can be wrien as follows, U U i Ui Pk v (6) x x i x In he equaions above C, C 1, C 2, k, are model consans and he values: (1) (2) (3)

4 772 Yongxiang Dong e al. / Procedia Engineering 31 (2012) C 0.09 C, C, Numerical Solver and Boundary condiions 1, k 1.3, The commercially available CFD solver FLUENT was used in his simulaion. In he compuaion he pressure based implici seady solver is used and he pressure-velociy coupling algorihm is SIMPLEC. For accuracy second order mehod was used for pressure, momenum and he urbulence viscosiy discreizaion. The MRF is a seady-sae approximaion in which individual cell zones can be assigned differen roaional or ranslaional speeds. The flow in each moving cell zone is solved using he moving reference frame equaions. If he zone is saionary (=0), he equaions reduce o heir saionary forms. In our work, he inerior flow field sub zone needs a roaional speed o realize he roor roaion and exerior flow field us be assigned a zero roaional speed because i is saionary. For he boundary condiions, he underwaer vehicle, duc and saor are saionary wall boundary relaive o he exerior flow field. The roor is moving wall relaive o exerior flow field and is roaional speed is he same as he inerior flow field. The inle and oule of he overflow field are given velociy inle and pressure oule respecively o realize a uniform flow field wih a consan speed. 3. Resuls Comparison of he simulaion resuls wih a previously conduced full scale model experimen is showed in Fig 3. As can be seen in Fig 3, he hrus resuls of he propulsion show good agreemen beween simulaion and experimen corresponding o differen roaional speed of he roor. The CFD model of he flow field for underwaer vehicle wih pump e hruser has been verified. 600 experimen daa simulaion daa Thrus (N) Roaional speed (r/m) Fig. 3. The comparison of pump e hruser hrus beween experimenal and simulaion

5 Yongxiang Dong e al. / Procedia Engineering 31 (2012) Fig. 4. Pressure disribuion of pump e hruser inerior field Fig 4 shows he conour plo of pressure field of he inerior flow field of he propulsion. From Fig 4, we can see ha hrus side of he roor has a high pressure and sucion side of he roor has a low pressure. This is why he propulsion can provide he hrus. As is known ha he poor propulsion performance could course a bad effec on he hydrodynamic characerisics of he underwaer vehicle [5]. Fig 5 shows he piching momen coefficien comparison of wihin (referenced by B+P) and wihou (referenced by B) propulsion. The piching momen coefficien a differen angle of aack reduces 3% generally afer he propulsion was concerned. From he figure we can found ha he propulsion has lile effec on he sabiliy of he underwaer vehicle. Tha is, he propulsion in his paper has a good design. Piching momen coefficien B B+P Angle of aack Fig. 5. Comparison of piching momen coefficien beween model B and model B+P

6 774 Yongxiang Dong e al. / Procedia Engineering 31 (2012) Conclusion From his sudy of CFD applicaion, we can conclude ha he overall flow field of underwaer vehicle wih pump e hruser can be well simulaed by muliple reference frames (MRF) of FLUENT. Through analyzing he flow field, i has been found ha Lif coefficien and pich momen coefficien changed less han 3%. The simulaion resuls could be regarded as an imporan reference in he opimal design of pump e hruser and he hydrodynamic characerisics of underwaer vehicle. References [1] Tiansen LI. Torpedo Manoeuvrabiliy;2007. [2] Jingping. XIAO, Hua. JIN. Power effec research on orpedo model wih couner-roaion pusher propeller. Experimens and Measuremens in Fluid Mechanics 2001;15:3. [3] Zhirong ZHANG, Baiqi LI. Inegral calculaion of viscous flow around ship hull wih propeller. Journal of Ship Mechanics 2004;8:5. [4] Zhihua LIU, Ying XIONG, Jinming Ye. Sudy on he predicion of propeller open-waer performance using RANS formula and muli-block hybrid meshes. Journal of hydrodynamics 2007;22:4. [5] Tao ZHANG, Chenun YANG, Baowei SONG. Invesigaionson he numerical simulaion mehod forhe open-waer performance of conra-roaingpropellers based on he MRF model. Journal of Ship Mechanics 2010;14:8.