The Specialist Com m ittee on W ake Fields Final Report 25 th International Towing Tank Conference – 14-20 September 2008, Fukuoka
Mem bership � Dr. Jin Kim (Chairman) MOERI, Korea � Dr. Thomas C. Fu (Secretary) NSWCCD, U.S.A. � Dr. Tomasz Bugalski Ship Design and Research Center (CTO-SA), Poland � Dr. Munehiko Hinatsu NMRI, Japan � Dr. Fabio Di Felice INSEAN Italian Ship Model Basin, Italy 25 th International Towing Tank Conference – 14-20 September 2008, Fukuoka
Contents • I ntroduction • Task 1 : Survey of numerical methods for the prediction of wake-fields at model and full scale. • Task 2 : Review the experimental methods of determining the velocity distribution in the wake. • Task 3 : Development of procedures for measuring the velocity distribution in the wake at model-scale. • Task 4 : Review and update the existing guidelines for the simulation of the wake-field for cavitation testing • Task 5 : Guidelines for the use of PIV in determining the velocity distribution in the wake. • Recom m endations to the Conference 25 th International Towing Tank Conference – 14-20 September 2008, Fukuoka
I ntroduction • Review of the numerical prediction and experimental measurement of wake-fields. • Emphasis was on completeness – Not constrained to the period since the 24th ITTC Meeting • Model and Full scale Computation – Much attention was paid to the numerical prediction of wakes at full-scale • Measurements for – Simulated wake verification, – Computational Fluid Dynamics (CFD) validation, – Basic research • Review and development of ITTC procedures of simulated wakes. • Generation, • Use • Verification (measurement) 25 th International Towing Tank Conference – 14-20 September 2008, Fukuoka
I ntroduction • Review of all of the ITTC Procedures to standardize the procedures for generating and assessing simulated wakes. – Procedure 7.5-02-03-03.1: Model-Scale Cavitation Test Cavitation Induced Pressure – Procedure 7.5-02-03-03.3: Fluctuations Model Scale Experiments – Procedure 7.5-02-03-03.5: Cavitation Induced Erosion on Propellers, Rudders and Appendages Model Scale Experiments – Procedure 7.5-02-03-03.6: Podded Propulsor Model- Scale Cavitation Test 25 th International Towing Tank Conference – 14-20 September 2008, Fukuoka
I ntroduction • Development of wake-field measurement procedures – 5-Hole Pitot Tubes, – Laser Doppler Velocimetry (LDV) – Particle Image Velocimetry (PIV)* – Full-Scale* * Determined to be not mature enough for ITTC procedures • The committee’s recommendations 25 th International Towing Tank Conference – 14-20 September 2008, Fukuoka
Task 1 : Survey of num erical m ethods for the prediction of w ake- fields at m odel and full scale. • December 2005 saw the successful conclusion of the three-year E uropean F ull-scale F l O w R esearch and T echnology ( EFFORT ) project . – Principal objective was to validate CFD predictions of wake field of ships by comparison with experimental data. – Full-scale flow measurements were conducted by MARIN, Netherland for ‘Nawigator XXI’, a single screw research vessel. – ‘Uilenspiegel’, a hopper dredger of Dredging International, Netherland; a twin-screw vessel with bossings, exposed shaft hoses, shaft support struts and ducted propellers. – A dedicated LDV system was used, operating through windows flush-mounted in the hull. – Parallel model experiments were carried out, including • Pitot measurements by HUT, Finland • PIV measurements by CTO, Poland • Wave pattern measurements using a laser sheet technique by NTUA, Greece. 25 th International Towing Tank Conference – 14-20 September 2008, Fukuoka
Task 1 : Survey of num erical m ethods for the prediction of w ake- fields at m odel and full scale. Naw igator XXI 25 th International Towing Tank Conference – 14-20 September 2008, Fukuoka
Task 1 : Survey of num erical m ethods for the prediction of w ake- fields at m odel and full scale. Uilenspiegel 25 th International Towing Tank Conference – 14-20 September 2008, Fukuoka
Task 1 : Survey of num erical m ethods for the prediction of w ake- fields at m odel and full scale. • On the CFD front, RANS computations were requested for full-scale Reynolds numbers. • An internal EFFORT workshop compared results and stimulated improvements of the accuracy and applicability of several codes. • All model and full-scale experimental data, for the two new ships and five existing ones, were then used to study the achievable level of accuracy of the predicted wake fields at full-scale. • Several of the CFD codes were found to predict the full- scale flow relatively accurately, provided fine enough grids were used. • An important contribution has been made to the practical use of CFD for prediction of the full-scale viscous flow and propeller action. 25 th International Towing Tank Conference – 14-20 September 2008, Fukuoka
Task 1 : Survey of num erical m ethods for the prediction of w ake- fields at m odel and full scale. • The LEADI NG EDGE project aimed at providing tools for predicting and scaling the development and evolution of propeller blade tip vortices. • Eight participants have calculated the flow around one or more of the propellers, at model scale as well as at full scale using RANS codes. • Complementary experiments have been carried out: – a conventional propeller (used as a reference propeller), – a modern high-skew propeller – a tip-plated propeller. • Validation measurements at model scale have been obtained. These measurements include – traditional propulsion, open-water and cavitation inception tests – flow field measurements with 3D Particle Image Velocimetry • The LEADI NG EDGE project has shown that viscous flow analysis for ship propellers is feasible and useful. 25 th International Towing Tank Conference – 14-20 September 2008, Fukuoka
Task 1 : Survey of num erical m ethods for the prediction of w ake- fields at m odel and full scale. Viscous Flow Com putations at Model Scale • The 2005 CFD Workshop Tokyo - wake computations – MOERI container ship (KCS), – MOERI tanker ship (KVLCC2M) – DTMB 5415 combatant ship – Theses efforts provide examples of the current CFD capability to simulate the viscous wake-field around a ship. – RANS – Turbulence model: two-equation & RSM models 25 th International Towing Tank Conference – 14-20 September 2008, Fukuoka
Task 1 : Survey of num erical m ethods for the prediction of w ake- fields at m odel and full scale. Viscous Flow Com putations at Model Scale • Alin et al. (2003): LES for Submarine hull • Bensow et al. (2006) investigated a comparative study of RANS, DES and LES. one of case is a flow past an axisymmetric submarine hull (SUBOFF). For the axisymmetric hull, RANS and DES show reasonable results but somewhat inferior when compared to the LES. 25 th International Towing Tank Conference – 14-20 September 2008, Fukuoka
Task 1 : Survey of num erical m ethods for the prediction of w ake- fields at m odel and full scale. Viscous Flow Com putations at Model Scale • Bugalski & Kraskowski (2006) presents validation of the RANSE wake computations for the training vessel Nawigator XXI and the dredger Uilenspiegel – result of work for EFFORT project. standard k- ε Menter’s k- ω RSM 25 th International Towing Tank Conference – 14-20 September 2008, Fukuoka
Task 1 : Survey of num erical m ethods for the prediction of w ake- fields at m odel and full scale. Total or Effective W ake • RANS + VLM (Propeller model) • Study on total wake & Propeller-Hull Interaction • Hino (2006) – Trim & Sinkage – Self-propulsion factors • Kimura et al. (2007) – Self-propulsion factors Wake behind a propeller (Hino) 25 th International Towing Tank Conference – 14-20 September 2008, Fukuoka
Task 1 : Survey of num erical m ethods for the prediction of w ake- fields at m odel and full scale. Total or Effective W ake • Kim et al. (2006) – RANS + VLM – Overset grid for rudder block – Self-propulsion factors – Hull-Propeller-Rudder Interaction 25 th International Towing Tank Conference – 14-20 September 2008, Fukuoka
Task 1 : Survey of num erical m ethods for the prediction of w ake- fields at m odel and full scale. Appendage/ Propeller w ake • Bensow et al. (2006) shows propeller near wake analysis using LES. LES on a rotating mesh has been applied for the simulation of the flow around a propeller, focusing on an investigation of the velocity field in the near wake. • Regnstrom & Bathfield (2006) presents drag and wake prediction for ships with appendages using an overlapping grid method. The work was done for the EFFORT project. 25 th International Towing Tank Conference – 14-20 September 2008, Fukuoka
Task 1 : Survey of num erical m ethods for the prediction of w ake- fields at m odel and full scale. Viscous Flow Com putations at Full Scale • Visonneau (2005) presents studies carried out in one of the major EFFORT project. • Visonneau et al. (2007) shows application of the developed method to simulation of the full scale flow on two appended hull configurations. RANS Computation for Uilenspiegel 25 th International Towing Tank Conference – 14-20 September 2008, Fukuoka
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