Coefficients of Propeller-hull Interaction in Propulsion System of Inland Waterway Vessels with Stern Tunnels

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1 hp:// he Inernaional Journal on Marine Navigaion and Safey of Sea Transporaion Volume 8 Number 3 Sepember 214 DOI: / Coefficiens of Propeller-hull Ineracion in Propulsion Sysem of Inland Waerway Vessels wih Sern Tunnels J. Kulczyk & T. Tabaczek Wrocław Universiy of Technology, Wrocław, Poland ABSTRACT: Propeller hull ineracion coefficiens he wake fracion and he hrus deducion facor play significan role in design of propulsion sysem of a ship. In he case of inland waerway vessels he reliable mehod of predicing hese coefficiens in early design sage is missing. Based on he oucomes from model ess and from numerical compuaions he presen auhors show ha i is difficul o deermine uniquely he rends in change of wake fracion and hrus deducion facor resuling from he changes of hull form or operaing condiions. Nowadays he resisance and propulsion model ess of inland waerway vessels are carried ou rarely because of relaively high coss. On he oher hand, he degree of developmen of compuaional mehods enables o esimae he reliable values o ineracion coefficiens. The compuaions referred o in he presen paper re carried ou using he auhors own sofware HPSDKS and he commercial sofware Ansys Fluen 1 INTRODUCTION For correc design of propulsion sysem wih screw propeller for inland waerway vessel he precise deerminaion of propeller hull ineracion coefficiens is required. These coefficiens are he wake fracion (denoed wih w) and he hrus deducion facor (denoed wih ). The former coefficien describes he acual inflow velociy o propeller, ha is usually lor han ship speed because of wake behind he ship. The laer describes he increase in hull resisance due o he sucion of propeller, and is used o deermine he hrus required o achieve he assumed ship speed. Propeller hrus a given ship speed is usually greaer han he resisance of od ship hull. The proporion (1 )/(1 w) in naval archiecure is called he hull efficiency. Acually, i is no he efficiency in meaning of echnology. I is raher he coefficien ha accouns for he influence of propellerhull hydrodynamic ineracion on he efficiency of propulsion sysem. Hull efficiency greaer han 1. means ha here is he beneficial muual fi of propeller and hull, and increases he overall efficiency of propulsion sysem. Errors in deerminaion of values of ineracion coefficiens in he course of ship design are bad for operaion of propulsion sysem in real operaing condiions [8]. The error in deerminaion of wake fracion resuls in errors in advance speed VA and in open waer efficiency of propeller η. The difference been assumed and acual value of efficiency is deermined by he following equaion: d o w dw 1 KQ 1 KT 1 J o 1 w w KQ J KT J J (1) 377

2 and affecs he ship speed: dv w dw (2) V 1 w w where: η open waer efficiency of propeller, J advance coefficien of propeller, w wake fracion, KT hrus coefficien, KQ orque coefficien, V ship speed. When w<.5 he relaive error in speed dv/v is smaller han he error in wake fracion dw/w. Posiive value of dw/w resuls in higher acual speed. In predicion of ship speed he underesimaed values of wake fracion may become beneficial, especially when he highes possible ship speed is he goal of propeller design. For sea going ships here is a number of reliable empirical formulae in he lieraure for deerminaion of values of ineracion coefficiens. Those formulae are based on he resuls of sysemaic model ess wih various hull forms. For inland waerway vessels such formulae are missing because of lack of sysemaic model ess. The effecs of waer deph, ship speed (propeller loading) and heigh of sern unnel(s) on wake fracion and hrus deducion facor have no been sufficienly invesigaed. The oucomes from ess carried ou wih moor cargo vessel GUSTAW KOENIGS [1] show ha he effec of sream in waer on wake fracion and hrus deducion facor is also significan. Available oucomes from model ess and resuls of numerical compuaions are no numerous enough o predic he values of ineracion coefficiens reliably in he case of newly designed vessels or in he case of variable operaing condiions. 2 DETERMINATION OF INTERACTION COEFFICIENTS Wake fracion and hrus deducion facor for given ship are deermined using he resuls of resisance and propulsion model ess, he resuls of numerical compuaions, or empirical formulae. Model ess are ime consuming and expensive. In he case of inland waerway vessel he coss of model ess are high in comparison o he coss of ship design and consrucion. Therefore hey are carried ou rarely. Numerical compuaions using he commercial CFD sofware provide reliable resuls, bu are also labour consuming and require he efficien hardware. Compuaions are also expensive. Empirical formulae based on oucomes from numerous model ess and on daa from operaion of real vessels, are commonly used in early design sages, as ll as in real ime conrol of propulsion sysem. The mehods developed for sea going ships are precise enough owing o numerous experimenal daa from model ess. For inland waerway vessels he reliable empirical formulae are missing due o much less number of model ess carried ou in he pas.. The deerminaion of hrus deducion facor based on daa from model ess or resuls of numerical compuaions of ship flow (wih operaing propeller and wihou propeller) is sraighforward. Using values of hull resisance R and propeller hrus T he value of hrus deducion facor is calculaed according o is definiion: = (T R)/T. Two wake coefficiens are used in design of screw propellers: he nominal wake fracion (in propeller disk behind he hull od wihou propeller, denoed wih wn) and he effecive wake fracion (for propeller operaing in ship wake, denoed wih ). The nominal wake fracion represens he acual mean velociy of wake flow in propeller disk Vn. I is defined as proporion wn = (VS Vn)/VS, and is deermined based on direc measuremens or compuaions of flow velociy. The effecive wake fracion represens he men inflow velociy o he propeller operaing in ship wake or, oherwise he advance speed of propeller VA. I is defined as proporion = (VS VA)/VS, and accouns for he influence of he running propeller on flow in hull boundary layer and wake. Effecive wake fracion is deermined using he magniudes measured in propulsion es and he open waer hydrodynamic characerisics of propeller. Performance of propeller operaing in ship wake (hrus or orque) is compared o he performance of he same propeller in open waer, wih assumpion of hrus ideniy or orque ideniy, in order o deermine advance speed VA. Thrus ideniy is usually applied in model ess. Torque ideniy is applied o full scale measuremens when only orque is measured on propeller shaf. Values deermined wih he assumpion of orque ideniy may differ considerably from values deermined wih he assumpion of hrus ideniy. Recommended procedures prepared by he Inernaional Towing Tank Conference [9] sandardize he mehodology of deerminaion of propeller hull ineracion coefficiens. In he following secions he auhors presen he analysis of he influence of operaing condiions (i.e. ship loading, waer deph and ship speed) and heigh of sern unnel on propeller hull ineracion coefficiens for inland waerway vessels. The analysis is based on oucomes from model ess and resuls of numerical compuaions. I refers o convenional inland waerway cargo ships wih sern unnels moor cargo vessels and pushed barge rains made up of dumb barges coupled wih a pushboa. 3 INTERACTION COEFFICIENTS FOR MOTOR CARGO VESSELS Main pariculars and hull forms of considered moor cargo vessels are presened in Table 1 and in Figures 1 and 2. Model ess of moor cargo vessel BM DUISBURG [3] included he measuremens of flow velociy in propeller disk wihou propeller (nominal wake) and he measuremens of flow velociy in plane locaed in 378

3 disance.4 of propeller diameer in fron of operaing propeller (Fig. 1). Effecive wake fracion was deermined wih assumpion of hrus ideniy. Tess re carried ou a various operaing condiions (ship draugh, waer deph and ship speed see Table 1). Convenional resisance and propulsion ess re carried ou wih moor cargo vessel OBM [2]. Effecive wake fracion was deermined wih he assumpion of hrus ideniy as ll as orque ideniy, in wide range of ship speed, for he vessel sailing alone ( solo ) and coupled wih a single dumb barge ( kombi ). Model ess of OBM in boh arrangemens re also reproduced in numerical compuaions [7]. Tess and compuaions re carried ou a wo values of draugh, in deep and in shallow (h/t=1,56) waer. Resuls are presened in Table 2. Figue 1. Hull form of moor cargo vessel BM DUISBURG Figue 2. Hull form of moor cargo vessel OBM Table 1. Main pariculars and operaing condiions of model ships, [3], [2] Vessel BM DUISBURG OBM Scale 1 : : 16 LWL [m] B [m] T [m] CB [ ] h [m] V [m/s ] Propellers ype screw propeller duced propeller Ka4 55 D [ m ] P/D [ ].65.9 AE/AO [ ]

4 Table 2. Resuls of model ess and numerical compuaions Vessel BM DUISBURG OBM Scale 1 : : 16 T [m] h [m] h/t V [m/s] Fnh n [rps] Coefficiens of propeller hull ineracion Tes wn T Q wzp Compu. wn Fluen wzp Compu. wn HPSDK wzp T - effecive wake fracion based on hrus ideniy Q - effecive wake fracion based on orque ideniy wzp = (VS-Vzp)/VS where Vzp denoes he mean velociy in fron of operaing propeller, and VS is he corresponding ship speed wzp = (VS-Vzp)/VS where Vzp denoes he mean velociy in fron of operaing propeller, and VS is he corresponding ship speed OBM OBM : T=1.6m, deep waer,2,2,15,15,1,5 T=1.6m, deep w. T=2.36m, deep w. T=1.6m, h=2.5m,1, , ,5 -,1 -,1 OBM OBM : T=1.6m, deep waer,6,5,4,3,2,1 -, ,2 T=1.6m, deep w. T=2.36m, deep w. T=1.6m, h=2.5m,6,5,4,3,2,1 -, ,2 Figure 3. Wake fracion ( T) and hrus deducion facor () for moor cargo vessel OBM (in model scale),2,15 OBM : T=2.36m, deep waer,1, ,5 -,1 38

5 ,6,5,4,3,2,1 -,2 OBM : T=2.36m, deep waer -, ,2,15,1,5 -,1 OBM : T=1.6m, h=2.5m ,5,6,5,4,3,2,1 -,2 OBM : T=1.6m, h=2.5m -, Figure 4. Comparison of wake fracion ( T) and hrus deducion facor () for moor cargo vessel OBM sailing alone ( solo ) and coupled wih a single dumb barge ( kombi ),7,6,5,4,3,2,1 OBM 'soko' -, OBM T, T=1.6m, deep w. T, T=2.36m, deep w. T, T=1.6m, h=2.5m Q, T=1.6m, deep w. Q, T=2.36m, deep w. Q, T=1.6m, h=2.5m,7,6,5 T, T=1.6m, deep w. T, T=2.36m, deep w.,4 T, T=1.6m, h=2.5m Q, T=1.6m, deep w.,3 Q, T=2.36m, deep w.,2 Q, T=1.6m, h=2.5m,1 -, Figure 5. Comparison of effecive wake fracion deermined wih assumpion of hrus ideniy (T) and deermined wih assumpion of orque ideniy (Q) for moor cargo vessel OBM sailing alone ( solo ) and coupled wih a single dumb barge ( kombi ),3,25,2,15,1,5,3,25,2,15,1,5 BM-DUISBURG 2 2,5 3 3,5 T [m] BM-DUISBURG 2 2,5 3 3,5 T [m] Figure 6. The effec of ship loading (ship draugh) on wake fracion () and hrus deducion facor () for moor cargo vessel BM DUISBURG a consan deph of waer h=5.m (in model scale),3,25,2,15,1,5,35,3,25,2,15,1,5 BM-DUISBURG h [m] BM-DUISBURG h [m] Figure 7. The effec of waer deph on wake fracion () and hrus deducion facor () for moor cargo vessel BM DUISBURG a consan draugh T=2.5m (in model scale) When ship speed increases he effecive wake fracion is geing aker (Fig. 3). In deep waer, a speeds higher han 12km/h becomes almos seady. In shallow waer (h/t=1.56) he wake fracion decreases faser, and a speed of 12km/h (Fnh=.67) is considerably less han in deep waer, because of inensive sinkage and rim by sern. The change of draugh in deep waer does no affec he wake 381

6 fracion as far as op of sern unnel is below he free surface in calm waer. In arrangemen wih dumb barge ( kombi ) boh values and rends in change of he effecive wake fracion are almos he same as when sailing alone (Fig. 4). When ship speed increases he hrus deducion facor also increases (Fig. 3). In shallow waer he values are greaer han in deep waer. The effec of draugh a highes speed in deep waer is negligible. Based on daa shown in Fig. 4 one can no conclude he changes in hrus deducion facor caused by enlargemen of ship lengh (by coupling wih a barge). The diagrams shown in Fig. 5 illusrae he difference been values of wake fracion deermined wih he assumpion of hrus ideniy and deermined wih he assumpion of orque ideniy. The exen of model ess wih he moor cargo vessel BM DUISBURG allows o idenify he variaion of ineracion coefficiens caused by change of draugh in shallow waer (1.56 h/t 2.; see Fig. 6). When ship draugh increases he wake fracion evidenly decreases due o decreasing under keel clearance been ship and boom of waerway. A he same ime he hrus deducion facor slighly increases. Reducion of waer deph a consan ship draugh caused he akening of wake and inensificaion of propeller sucion (Fig. 7). Reducion of under keel clearance is considerable and one migh expec greaer difference been values of wake fracion. Hover, he rends are he same as in he case of reducion of under keel clearance by increasing ship draugh a consan waer deph, or in he case of ransiion from deep o shallow waer in ess wih moor cargo vessel OBM. 4 INTERACTION COEFFICIENTS FOR PUSHED BARGE TRAINS Model ess of pushed barge rains wih winpropeller pushboa and riple propeller pushboa re carried ou in research cenre in Duisburg [4], [5]. The win propeller pushboa was esed in rain wih 4 dumb barges arranged in wo rows, a barge draugh of 2.8m (.175m in model scale) and 3.2m (.2m in model scale). The riple propeller pushboa was esed in rain wih 6 dumb barges arranged in wo rows, a barge draugh of 3.m (. 188m in model scale). Numerical compuaions re carried ou using heoreical model described in [6], a he same operaing condiions as in model ess. Main pariculars of pushboas and dumb barge EUROPA II are given in Table 3. Hull forms of considered pushboas are shown in Figures 8 and 9. Table 3. Main pariculars of esed pushboas and dumb barges [4], [5] Vessel Twin Triple Dumb barge screw screw EUROPA II pushboa pushboa Scale 1 :16 1 : 16 1 : 16 LOA [m] LWL [m] B [m] T [m] CB [ ] Screw propeller z 4 4 D [m] P/D [ ] Ag/A [ ] h [m].3125 Table 4. Resuls of model ess and numerical compuaions Vessel Twin screw Triple screw pushboa pushboa h [m] T [m] (pushboa) TB [m] (dumb barges) h/tb V [m/s] Fnh n [rps] Cenral Side Side propeller propeller propeller (screw (duced prop.) prop.) Model es wn wzp Compu. wn (HPSDK) wzp KT

7 Figur 8. Hull form of win screw pushboa Figure 9. Hull form of riple screw pushboa The resuls of model ess and numerical compuaions are presened in Table 4. In he case of esed pushed barge rains in shallow waer he increase of barge draugh a consan waer deph caused increase of wake fracion. The rend is opposie o ha observed in he case of moor cargo vessels and described in he preceding secion. The reason is ha he draugh of pushboa remained unchanged and, in fac, i was he change of hull form and no only of ship draugh. Some regulariies in variaion of ineracion coefficiens observed in he case of moor cargo vessel do no refer o pushed barge rains. Moreover, in he case of pushboas ha operae a almos consan draugh, regardless of he draugh of barges, he heigh of unnels is usually greaer han draugh, in order o accommodae propeller of sufficien diameer. Tha is why he values of nominal and effecive wake fracion are, in general, greaer han in he case of moor cargo vessels where he op of sern unnel is below he free surface of waer. The effec of unnel heigh on coefficiens of propeller hull ineracion was sudied heoreically for virual pushboa of simplified hull form [7]. Main pariculars of virual pushboa are given in Table 5. The secion along he sern unnel of virual pushboa is shown in Fig. 6. According o he pracice in design of inland waerway vessels, he unnel heigh of 1.3m is considered he maximum applicable a ship draugh of 1.m. Table 5. Main pariculars of virual pushboa [7] Lengh, L [m] 2. Beam, B [m] 9. Draugh, T [m] 1. Heigh of unnel, hw [m] 1.1; 1.3; 1.5 Slope of unnel, [deg] 25 Figure 6. Secion along he sern unnel of virual pushboa 383

8 Three values of unnel heigh re considered (Table 6). For each heigh he diameer of duced propeller was deermined wih assumpion, ha nozzle is inegraed wih ship hull. Using he es daa of Ka4 7 screw series in nozzle 19A he propeller pich was designed so as o achieve maximum hrus a given advance speed VA=2.1m/s. Thrus of propeller and mean pressure gradien in propeller disk re deermined for hree values of ship speed, based on propulsive characerisics. The resuls are presened in Table 6. Table 6. Diameer and hrus of duced propellers designed for virual pushboa hw D Z n VS T p [m] [m] [m] [rps] [m/s] [kn] [kpa] Using CFD sofware Ansys Fluen and he acuaor disk wih pressure gradien o simulae he acion of propeller a series of numerical compuaions re carried ou a waer deph of 1.5 and 3.m. The values of nominal wake fracion and hrus deducion facor deermined for virual pushboa are presened in Table 7. Table 7. Nominal wake fracion and hrus deducion facor deermined for virual pushboa hw [m] VS [m/s] h/t wn CONCLUSIONS Due o he lile amoun of daa he conclusions are raher qualiaive han quaniaive and refer o model scale, hover, shall be valid also in full scale. The resuls of model ess and numerical compuaions show ha operaing parameers considered in his paper, i.e. ship loading (or corresponding ship draugh), waer deph and ship speed, affec he values of boh wake fracion and hrus deducion facor. Considering inland waerway vessels wih sern unnels ha do no rise above free surface of waer (hw < h), as moor cargo vessels wih full or parial loading, one may expec ha: The increase of ship speed in deep as ll as in shallow waer causes he decrease of wake fracion and increase of hrus deducion facor. A higher speeds in deep waer he wake fracion becomes seady. In shallow waer he wake fracion decreases unil deph Froude number (Fnh = VS/(gh) 1/2 ) reaches he value of.65. Operaion of cargo vessels a higher speed is unprofiable and may cause grounding due o inensive rim and sinkage of ship. Change of ship loading (and corresponding change of ship draugh) in deep waer does no affec he propeller hull ineracion coefficiens. In shallow waer boh he reducion of waer deph as ll as he increase of ship draugh resul in decrease of under keel clearance and in he same rends in variaion of ineracion coefficiens: when he disance been hull and waerway boom (or h/t raio) decreases, wake fracion also decreases and hrus deducion facor increases. The effecive wake fracion deermined wih assumpion of orque ideniy differs significanly from ha deermined wih assumpion of hrus ideniy. In he case of pushed barge rains he change of barge loading (or change of barge draugh) does nor affec he draugh of pushboa, and implies he change of hull form. Regulariies in variaion of ineracion coefficiens observed in he case of moor cargo vessel may no obey in he case of pushed barge rains. The resuls of model ess and numerical compuaions also show ha he heigh of sern unnels affecs he flow around ship considerably, and, in consequence, he value of hrus deducion facor. REFERENCES [1] Graff, W.: Unersuchungen über Änderungen von Sog und Nachsrom auf beschranker Wasseriefe in sehenden und sromendern Wasser, Schiffsechnik, Bd. 8, H.44, 1961 [2] Badania modelo OBM, Cenrum Techniki Okręoj, Gdańsk 1975 [3] Luhra, G.: Unersuchung der Nachsromvereilung an einem 2 Schrauben Binnenguermoorschiff, Versuchsansal für Binnenschiffbau E.V., Duisburg, Berich Nr. 788 [4] Luhra, G.: Unersuchung der Nachsomvereilung eines im Verband schiebenden Schubboos in Pononform mi einer zcks Verbesserung zum Propeller geänderen Zwierumpf Unerwasserformgebung, Versuchsansal für Binnenschiffbau E.V., Duisburg, Berich Nr. 72 [5] Luhra, G.: Unersuchung der Nachsromverhälnisse an Drei und Vier Schrauben Schubbooen, Versuchsansal für Binnenschiffbau E.V., Duisburg, Berich Nr. 919 [6] Kulczyk, J.: Modelowanie numeryczne oddziaływań hydrodynamicznych w układzie napędowym saku śródlądogo, Prace Nauko Insyuu Konsrukcji i Eksploaacji Maszyn, Poliechnika Wrocławska, Seria: Monografie, Nr 17, Wrocław, 1992 [7] Kulczyk, J., Tabaczek, T., Zawiślak, M., Zieliński, A., Werszko, R.: Numeryczne modelowanie przepływu lepkiego wokół kadłuba saku śródlądogo na ograniczonej drodze wodnej, Insyu Konsrukcji i Eksploaacji Maszyn, Poliechnika Wrocławska, Rapor z serii Prepriny, Nr S 43/3, Wrocław, 23 [8] Kulczyk, J.; Winer, J.: Śródlądowy ranspor wodny, Oficyna Wydawnicza Poliechniki Wrocławskiej, Wrocław, 23 [9] Inernaional Towing Tank Conference: Qualiy Sysems Manual, Version 211, ITTC Recommended Procedures and Guidelines 384