Abstract
Computational and experimental methods were used to study a propeller coated with hydrophobic material and a propeller with a conventional surface for comparison. In CFD simulations, the blade surface mesh was arranged in a way to set non-slip or free slip wall boundary conditions with different proportions to define the level of surface slip. The conventional and the hydrophobic material propellers defined by different surface slip rates were simulated under different advance speed coefficients and different rotational speeds. Propeller performance results, blade pressure, and the Liutex vorticity distribution were studied. An experimental platform was established to study the velocity field around the propeller using a Particle Image Velocimetry (PIV) device. The CFD calculation results were compared with the PIV results. It was found that the calculation results using a 75% surface slip rate were closer to the experimental results. The calculation results show that the propeller coated with hydrophobic material has improved thrust and efficiency compared with the propeller with conventional material. The hydrophobic material can significantly reduce the low-speed region downstream of the propeller hub. The hub and the tip vortices shown by the Liutex are also significantly reduced. Those changes help to improve the propulsion efficiency.
Highlights
As one of the most important propulsion devices of ships, propellers are extensively studied by many researchers for different scenarios
The computed results of the conventional propeller and the propeller coated with the hydrophobic material with a surface slip rate of 75% were further postprocessed to show the vorticity defined by the Liutex [25]
For the propeller coated with the hydrophobic material, both the Particle Image Velocimetry (PIV) result shown in Figure 12c and CFD result assuming a 75% slip rate shown in Figure 12d show clearly a shortened low-speed region downstream of the propeller hub, represented by the dark blue region with a length of about 0.15 m, on the left part of the propeller hub
Summary
As one of the most important propulsion devices of ships, propellers are extensively studied by many researchers for different scenarios. Lee et al [9] conducted a study on selecting cavitation models for CFD prediction of propeller flows They found that the cavitation simulation had limitations, the simulation results of foam cavitation and sheet cavitation around the tip were good compared with experiment. Nouri et al [16] computed the drag reduction effect of some superhydrophobic surfaces in turbulent flow channels by using a slip length concept in the wall shear stress expression. Katsuno et al [19] conducted CFD research on a super-hydrophobic coated propeller and used the concept of boundary layer slip length to simulate the effect of hydrophobic slip. A concept of surface slip rate is used for setting surface boundary conditions in numerical simulation for flow of the propeller coated with a hydrophobic material. In order to save computing resources for the propeller, which has rotational periodicity, aIInnvooorldrudemerrteototshasvaetvcehoacmodmpoupntuientgitnhrgeisrrodeusorcufersacfecosyrfltoihnredtphereroppweroallpsere,slwelelhre,iccwthehdhiacashsrhotathasetiroconotaamtlipopenuraitoladptiieocrinitoya,-l domaaidnvi,coaitlsuy,mshaeovtwohlanutmihneadFthioganuterhetahd4ir.odTnohefetahcicorydmlinopfduaetractwyiolains dasleerldewoctmaesdasiaensleitcshteecdocomamspptohuseteadctoioomnfpaaulndtaoitnimonnaeiarnl ,rdoaost-ating wdtrhoohetmawsatsewmdtrhpuhtnhroahioereordhnaetiirmoawnnliegoDaenptproauinn,reantdmeionihannoglisDopdselniudnematdeisiithrFnannlsoeha,laligedrlemogtnewdihrsnwtunta,iahteoahrnboawinsemenuntiomuilohpiout4oeesnrueirim.untnrlnoretteFToadrehriparirsnhuratgeoeloyhtarensaulufdyellidttcderntnaidiohiieoratodilsnimeinmemia4onil5stnegmp.anDpate1gTbirarutne.tobho5hayrtettpohyDe[weuare2eudretndc2aolipanoolopo]ydoefndr.fmnmrrmaodtfT.aotahrhrpparTphaoliyeyetiuiehmeedsnnlltppeiiorllaassea[ter[rmotxh2o2rd5oir5uio2ep2DaaiipDit]usni]elslp.ene.sal1alTrl1altelT.woleoi5hn.wbesdrp5fhDaegor.coDetaey.TuthormlhayTlanhemrfeanadrahiderfsndsop.idriatenoudmoa0Toriiuotts.yumsih5isisteuottsoeDlihadsescntftrxoe.otlah1aatoeifmbrh3apdxetfyoDlteriipabhuapuoldnsoeoalespnrotnswuaoliedomesgnetlpnfdaatilntnaoaeyrhtedigehoyrntlnafr.iiltfearsoierhTirosrarsyrn0oyhmon1.i.5ats5eti3adTDiasrDtDnt0ryothhi,1ian..nmne5we3addeggDwpDarihroudirdae.ramnosooadroypetwomimaiasefufDirtlaaan5lsoiteiniyhDimnnrsoige,s,ffr5othDme,
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