APPLIED TURBULENCE MODELLING IN MARINE WATERS
A STEP TOWARDS THE NUMERICAL SIMULATION OF VISCOUS FLOWS AROUND SHIPS AT FULL SCALE RECENT ACHIEVEMENTS WITHIN THE EUROPEAN UNION PROJECT EFFORT 1 BLADE SHAPING FOR OFF DESIGN PERFORMANCE CAVITATION AND EFFICIENCY IN TWO DIMENSIONAL CASCADES 9 NUMERICAL SIMULATION OF FREE SURFACE WAVE INDUCED SEPARATION 22 BASIN DEVELOPMENT OF A PRACTICAL BOUNDARY ELEMENT CODE FOR HYDRODYNAMIC ANALYSIS 30 VOF DYNAMIC MESH SIMULATIONS OF UNSTEADY SHIP HYDRODYNAMICS 45 SECOND ORDER WAVE FORCES AND FREE SURFACE ELEVATION AROUND A MOORED SHIP IN STEEP UNI DIRECTIONAL AND SPREAD WAVES 50 NUMERICAL SIMULATION OF YAW EFFECT 56 COMPARISON BETWEEN RANSE CALCULATIONS AND PANEL METHOD RESULTS FOR THE HYDRODYNAMIC ANALYSIS OF MARINE PROPELLERS 61 CONSIDERATION ON DEVIATIONS IN TORQUE PREDICTION FOR PROPELLERS AND WATERJETS WITH RANS CODES 74 INFLUENCE OF SCALE EFFECTS ON THE HYDRODYNAMIC CHARACTERISTICS OF PROPELLERS 83 PREDICTIONS OF THE THRUST AND TORQUE PERFORMANCE FOR TWO PROPELLER BLADES USING COMPUTATIONAL FLUID DYNAMICS 109 BEHAVIOUR OF SHIP FUNNEL EXHAUST IN THE WAKE OF A BLUFF BODY 118 THE EFFECT OF SHIP SHAPE AND ANEMOMETER LOCATION ON WIND SPEED MEASUREMENTS OBTAINED FROM SHIPS 128 CONTENTS A STEP TOWARDS THE NUMERICAL SIMULATION OF VISCOUS FLOWS AROUND SHIPS AT FULL SCALE RECENT ACHIEVEMENTS WITHIN THE EUROPEAN UNION PROJECT EFFORT SUMMARY THE EFFORT EUROPEAN FULL SCALE FLOW RESEARCH AND TECHNOLOGY PROJECT IS FUNDED BY THE EUROPEAN FRAMEWORK 5 PROGRAM AND AIMS AT THE RE NEMENT AND VALIDATION OF CFD PREDICTION METHODS FOR THE VISCOUS OW AROUND A SHIP HULL AT FULL SCALE AND THEIR INTRODUCTION INTO PRACTICAL SHIP AND PROPELLER DESIGN THE EMPHASIS IS ON PREDICTING THE FULL SCALE VISCOUS OW ELD AROUND A SHIP INCLUDING THE EVALUATION OF THE FREE SURFACE THE WAKE ELD THE HULL PROPELLER INTERACTION THE RESISTANCE AND THE POWER RANS COMPUTATIONS DO OFFER THAT POSSIBILITY AND SUCH FULL SCALE VISCOUS OW COMPUTATIONS HAVE STARTED TO BE USED IN PRACTICAL SHIP DESIGN BUT HOW ACCURATE THESE PREDICTIONS ARE IS NOT REALLY KNOWN VALIDATION OF FULL SCALE SHIP VISCOUS OW PREDICTIONS HAS GENERALLY BEEN INSUF CIENT SO FAR MAINLY DUE TO THE VIRTUAL ABSENCE OR DIF CULT ACCESSIBILITY OF SUITABLE FULL SCALE EXPERIMENTAL OW ELD DATA SUCH AS WAKE ELD DATA THIS IS THE FUNDAMENTAL POINT THAT EFFORT AIMS TO ADDRESS THE PAPER PRESENTS STUDIES CARRIED OUT IN ONE OF THE MAJOR WORK PACKAGES WHICH HAD THREE MAIN OBJECTIVES I TO DEVELOP AND IMPLEMENT THE APPROPRIATE PHYSICAL MODELLING FOR FULL SCALE OWS II TO PERFORM NUMERICAL STUDIES OF FULL SCALE OWS AROUND A REAL SHIP TO CHECK THE ROBUSTNESS AND THE ACCURACY OF THE SIMULATION TOOLS IN FULL SCALE OW CONDITIONS III TO ISSUE RECOMMENDATIONS TO PREPARE THE SIMULATION TOOLS TO BE USED FOR CFD VALIDATION AT SHIP AND MODEL SCALE IV TO DEVELOP AND IMPLEMENT THE APPROPRIATE PHYSICAL MODELLING FOR FULL SCALE OWS 1 INTRODUCTION HYDRODYNAMIC ASPECTS PLAY AN IMPORTANT ROLE IN THE QUALITY OF A SHIP DOMINANT CRITERIA FOR THE HULL FORM DESIGN OF MANY SHIPS ARE THE RESISTANCE AND POWERING PERFORMANCE IN ADDI TION THE OCCURENCE OF NOISE AND VIBRATIONS IMPORTANT FOR THE COMFORT LEVEL FOR CREW AND PASSENGERS OFTEN HAVE AN HYDRO DYNAMIC CAUSE STEMMING FROM THE OPERATION OF THE PROPELLER IN THE OW ELD BEHIND THE SHIP HULL CRITICAL INFORMATION TO EVALUATE AN INDUSTRIAL CON GURATION IS THE KNOWLEDGE OF THE OW IN THE AFT PART OF A SHIP AND IN ITS NEAR WAKE IN SITUATIONS AS CLOSE AS POSSIBLE TO THE REALITY THEORETICALLY COMPUTA TIONAL FLUID DYNAMICS CFD TOOLS CAN PROVIDE A SOLUTION TO THESE QUESTIONS AND THE USE OF CFD TOOLS FOR SIMULATING THE OW AROUND A SCALED SHIP MODEL WITH OR WITHOUT PROPELLER IS MORE AND MORE FREQUENT HOWEVER SUCH MODEL SCALE COM PUTATIONS ARE SUBJECT TO THE SAME DRAWBACKS AS THOSE INTRO DUCED BY THE SCALING PROCEDURES TO MAKE A REAL STEP FOR WARD IN PREDICTION ACCURACY IT IS MANDATORY TO USE ACCURATE AND RELIABLE VISCOUS OW SOLVERS FOR THE ACTUAL FULL SCALE SHIP IN THE DESIGN PROCESS VISCOUS OW COMPUTATIONS FOR THE FULL SCALE SHIP IS INHIBITED BY UNCERTAINTY ABOUT THE PROPER PHYSICAL MODELLING FOR FULL SCALE SHIP OWS DIF CULT ACCESSIBILITY OF FULL SCALE EXPERIMENTAL DATA TO VALIDATE THE COMPUTATIONS NUMERICAL DIF CULTIES ASSOCIATED WITH THE USE OF VERY LARGE ASPECT RATIO GRIDS REQUIRED TO CAPTURE THE VISCOUS EFFECT AT FULL SCALE THEREFORE THE AIMS OF THE EUROPEAN PROJECT EFFORT EUROPEAN FULL SCALE FLOW RESEARCH AND TECHNOLOGY WHICH GROUPS TOGETHER THREE TECHNICAL CENTERS MARIN THE PROJECT MANAGER HSVA AND CTO VE UNIVERSITIES ECN CNRS NTUA HUT CTH AND THE MARITIME UNI VERSITY OF SZCZECIN FOUR INDUSTRIAL PARTNERS IHC HOLLAND N V ROLLS ROYCE KAMEWA KVAERNER MASA YARDS VAN VO ORDEN GIETERIJ B V AND BASSIN D ESSAI DES CAR NES AND ONE CLASSI CATION SOCIETY LLOYD S REGISTER ARE TO EXTEND IN A COLLABORATIVE WAY THE EXISTING CFD CODES TO PREDICT THE OW AROUND SHIP HULLS AT FULL SCALE TO CARRY OUT A FULL SCALE MEASUREMENT CAMPAIGN IN WHICH EXTENSIVE LDV OW MEASUREMENTS WILL BE DONE AT SEA ON BOARD OF TWO VESSELS TO COLLECT THE MOST COMPLETE POSSIBLE SET OF FULL SCALE OWS FO CFD VALIDATION AND TO ESTABLISH THE LEVEL OF ACCURACY AND IMPROVE THE MODELLING TO APPLY THE CFD TOOLS TO DESIGN STUDIES PROPOSED BY THE INDUSTRIAL PARTICIPANTS WHICH SUPPORT THE PROJECT MORE UP TO DATE INFORMATION ABOUT THE PROGRESS ACHIEVED IN THIS EUROPEAN PROJECT MAY BE FOUND IN THE EFFORT WEB SITE HOSTED BY MARIN HTTP WWW MARIN NL THIS PAPER IS MORE SPECI CALLY DEVOTED TO THE CFD DEVELOPMENT WORK PERFORMED IN WORKPACKAGE 3 WP3 WHICH WAS FOCUSED ON SOME PARTICULAR ASPECTS OF RANS SOLVERS THAT PLAY AN IMPOR TANT ROLE IN THE VALIDATION FOR FULL SCALE OR THAT REQUIRE FURTHER STUDY BEFORE THEY CAN BE APPLIED RELIABLY FOR FULL SCALE FREE SURFACE EFFECTS ON THE VISCOUS OW WILL PLAY A ROLE ALBEIT PERHAPS LIMITED A SPECI C TASK HAS BEEN INCLUDED TO STUDY THE POSSIBILITY TO INCORPORATE THIS EFFECT FOR FULL SCALE SINCE THIS HAD NOT YET BEEN DEMONSTRATED TURBULENCE MODELLING PLAYS A DECISIVE ROLE IN THE QUAL ITY OF THE WAKE ELD PREDICTION AT MODEL SCALE AND MAY 1 BE EXPECTED TO DO SO AT FULL SCALE AS WELL SINCE THE POS SIBILITY TO APPLY ALL RELEVANT TURBULENCE MODELS AT FULL SCALE REYNOLDS NUMBERS HAD NOT BEEN ESTABLISHED THIS IS ADDRESSED IN ANOTHER TASK A REPRESENTATION OF THE PROPELLER EFFECT WILL NOT BE PAR TICULARLY DIFFERENT AT FULL SCALE THAN AT MODEL SCALE BUT IS NEEDED FOR MAKING A COMPARISON OF PREDICTIONS WITH THE TOTAL WAKE MEASUREMENTS TO BE CARRIED OUT THERE FORE A SMALL DEVELOPMENT TASK ADDRESSES THIS SUBJECT BUT FOR THE SAKE OF BREVITY THE RESULTS RELATED TO THIS TASK ARE NOT DESCRIBED IN THIS PAPER 2 COMPUTATIONAL APPROACHES 2 1 THE DIFFERENT FLOW SOLVERS THE COORDINATOR OF THE WORKPACKAGE WAS CNRS AND THE PAR TICIPANTS WERE HUT CTH NTUA MARIN AND HSVA THE LIST OF THESE CFD GROUPS SELECTED ACCORDING TO RELEVANT CFD CAPABILITIES AND EARLIER WORK WITH CFD TOOLS IS PROVIDED WITH TAB 1 AND TAB 2 NOTATIONS NS STANDS FOR NAVIER STOKES FS FOR FREE SURFACE AND NLP FOR NON LINEAR POTEN TIAL TABLE 1 PARTNERS IN WP3 PARTNER NAME ABBREVIATION COUNTRY CHALMERS UNIVERSITY CHALMERS S OF TECHNOLOGY CENTRE NATIONAL CNRS F RECHERCHE SCIENTI QUE HAMBURGISCHE SHIFFBAU HSVA D VERSUCHS ANSTALT HELSINKI UNIVERSITY HUT FIN OF TECHNOLOGY MARITIME RESEARCH MARIN NL INSTITUTE NETHERLANDS NATIONAL TECHNICAL NTUA G UNIVERSITY OF ATHENS TABLE 2 CONTRIBUTORS AND CFD TOOLS ORGANIZATION CODE NOTES CHALMERS CHAPMAN NS CODE NO FS CNRS ISIS NS CODE FS CAPTURING HSVA COMETA NS CODE FS CAPTURING HUT FINFLO NS CODE FS TTING MARIN RAPID NLP CODE MARIN PARNASSOS NS CODE XED FS NTUA PARALOS NS CODE FS TTING ACOMMERCIAL CODE MORE DETAILED INFORMATION ABOUT THE NUMERICAL STRATEGIES IMPLEMENTED IN THE RESPECTIVE SOLVERS MAY BE FOUND IN THE FOLLOWING REFERENCES 1 2 FOR THE CODE DEVELOPPED BY NTUA 3 FOR COMET AND 4 FOR THE STUDIES CARRIED OUT IN HSVA 5 6 FOR THE CODE USED BY HUT 7 8 FOR THE APPROACH FOLLOWED BY MARIN 9 FOR CTH AND 10 FOR THE CODE DEVELOPPED BY CNRS 3 FREE SURFACE FULL SCALE COMPUTATIONS 3 1 DESCRIPTION OF THE TEST CASE THE RESEARCH VESSEL SELECTED FOR THIS STUDY IS THE NAWIGATOR XXI OPERATED BY THE MARITIME UNIVERSITY OF SZCZECIN THE VESSEL IS DESIGNED FOR RESTRICTED NAVIGATION ON THE BALTIC AND NORTH SEAS WITHIN 200NM FROM THE NEAREST SHELTER AND THE MAIN DESTINATION OF THE SHIP IS TO TRAIN STUDENTS FOR FUTURE WORK AS DECK OF CERS ENGINEERS AND SHIP ELECTRICIANS FIG URE 1 SHOWS THE REAL VESSEL FIGURE 1 THE TRAINING AND RESEARCH SHIP NAWIGATOR XXI THIS VESSEL IS CHARACTERISED WITH THE FOLLOWING PARAMETERS LENGTH L 55 155M DRAFT D 3 15M WETTED SURFACE SDW L 665 5 M2 SPEED 12 KNOTS RE 340 106 FR 0 265 NUMERICAL GRIDS ARE GENERATED FROM AVAILABLE CAO DATABASE SEE FIG 2 FOR A GLOBAL VIEW OF THE HULL X Y Z FIGURE 2 NAWIGATOR XXI 3D VIEW FREE SURFACE CAPTURING 3 2 THE VARIOUS COMPUTATIONAL STRATEGIES THE CFD PARTNERS PARTICIPATING IN THIS COLLABORATIVE WORK REPRESENT THE WHOLE SPECTRUM OF THE COMPUTATIONAL STRATE GIES FOR COMPUTING VISCOUS FREE SURFACE OWS MARIN USES APPLIED TURBULENCE MODELLING IN MARINE WATERS 2 A COMPOSITE APPROACH WHICH IS BASED ON THE COMPUTATION OF THE FREE SURFACE BY A NON LINEAR POTENTIAL THEORY AND THEN USES THIS PRESCRIBED FREE SURFACE AS A XED BOUNDARY FOR THE VISCOUS OW COMPUTATIONS HUT AND NTUA COMPUTE THE VISCOUS FREE SURFACE OW WITH A FREE SURFACE TTING ALGO RITHM WHICH MEANS THAT ONLY THE OW OF WATER IS COMPUTED WITH ADEQUATE PHYSICAL BOUNDARY CONDITIONS ON AN UNKNOWN FREE SURFACE WHICH RESULTS FROM THE COMPUTATIONS AN AU TOMATIC REGRIDDING STRATEGY IS THEN NEEDED TO UPDATE THE SHAPE OF THE FREE SURFACE BOUNDARY DURING THE COMPUTATIONS HSVA AND CNRS HAVE CHOSEN TO USE A FREE SURFACE CAPTUR ING METHODOLOGY WHICH COMPUTES THE OW IN AIR AND WA TER NO REGRIDDING IS THEREFORE NECESSARY AND WAVE BREAKING MAY BE SIMULATED THE ACCURACY OF THE COMPUTATIONS IS STRONGLY DEPENDENT ON THE SPECI C COMPRESSIVE DISCRETISA TION SCHEMES WHICH ARE USED TO DISCRETIZE THE CONCENTRATION TRANSPORT EQUATION WHICH CHARACTERIZES THE PRESENCE OF AIR OR WATER 3 3 GLOBAL VIEWS OF THE FREE SURFACE FIGURES 3 AND 4 SHOW A GLOBAL VIEW OF THE FREE SURFACE AND WALL STREAMLINES COMPUTED BY CNRS WITH A FREE SURFACE CAPTURING METHODOLOGY FOR MODEL AND FULL SCALES RESPEC TIVELY ONE CAN NOTICE SLIGHT DIFFERENCES ON THE POSITIONNING OF THE MAIN CONVERGENCE LINE WHICH REFER TO THE DIFFERENT IN TENSITY OF THE LONGITUDINAL VORTEX THE STERN WAVE HEIGHT IS ALSO LARGER AT FULL SCALE THAN AT MODEL SCALE A FACT ON WHICH WE WILL COME BACK IN THE REMAINDER OF THIS ARTICLE FIGURE 3 FREE SURFACE AND WALL STREAMLINES AT MODEL SCALE FIGURES 5 AND 6 SHOW A GLOBAL VIEW OF THE FREE SURFACE ELE VATIONS AROUND THE NAWIGATOR AT 12 KNOTS OBTAINED BY HSVA AND CNRS BOTH TEAMS USING THE FREE SURFACE CAPTURING STRAT EGY THESE COMPUTATIONS ARE PERFORMED ON IDENTICAL GRIDS COMPRISING ROUGHLY 3 MILLION POINTS AND DESPITE DIFFERENT DISCRETISATION SCHEMES AND CODES THE RESULTS APPEAR QUITE SIMILAR THE SECOND SET OF RESULTS G 7 AND 8 OBTAINED BY NTUA AND HUT IS REPRESENTATIVE OF THE FREE SURFACE TTING STRAT EGY ONE MAY NOTICE THE ATTENUATION OF THE WAVES IN THE FAR ELD WHICH IS LIKELY DUE TO THE LACK OF GRID POINTS IN THIS REGION AND IS NOT RELATED TO THE FREE SURFACE TTING METHODOL OGY LASTLY GURE 9 SHOWS THE FREE SURFACE ELEVATION COM FIGURE 4 FREE SURFACE AND WALL STREAMLINES AT FULL SCALE X Y 60 40 20 0 20 0 10 20 30 40 0 5 0 4 0 3 0 2 0 1 0 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 1 0 1 1 1 2 1 3 HSVA FS K W SST 12 KNOTS WAVE ELEVATIONS FIGURE 5 WAVE ELEVATIONS HSVA 12 KNOTS FS CAPTURING X Y 60 40 20 0 20 0 10 20 30 40 0 5 0 4 0 3 0 2 0 1 0 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 1 0 1 1 1 2 1 3 CNRS FS K W SST 12 KNOTS WAVE ELEVATIONS FIGURE 6 WAVE ELEVATIONS CNRS 12 KNOTS FS CAPTURING X Y 60 40 20 0 20 0 10 20 30 40 0 5 0 4 0 3 0 2 0 1 0 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 1 0 1 1 1 2 1 3 HUT FS K W SST 12 KNOTS WAVE ELEVATIONS FIGURE 7 WAVE ELEVATIONS HUT 12 KNOTS FS TTING PUTED BY THE NON LINEAR POTENTIAL CODE RAPID DEVELOPED BY MARIN ONE MAY NOTICE THE CAPABILITY OF THIS METHODOLOGY TO CAPTURE ACCURATELY WAVES IN THE FAR ELD ALTHOUGH THESE SPECI C COMPUTATIONS ARE AFFECTED BY SOME SPURIOUS SHORT WAVES OCCURRING IN THE INNER SECTOR OF THE WAVE PATTERN APPLIED TURBULENCE MODELLING IN MARINE WATERS 3