Numerical Modeling of Ship-Propeller Interaction under - PowerPoint PPT Presentation

STAR Global Conference 2014 Vienna, Austria, March 17-19 Numerical Modeling of Ship-Propeller Interaction under Self-Propulsion Condition Vladimir Krasilnikov Department of Ship Technology, MARINTEK Trondheim, Norway Norsk Marinteknisk Forskningsinstitutt

Content of the presentation 1) Examples of research problems involving ship-propeller interaction 2) Approaches to numerical modeling of ship-propeller interaction 3) Validation example of the benchmark KCS container ship 4) Aspects of numerical modeling that require closer attention

1) Examples of research problems involving ship-propeller interaction

N = 0.736 Nominal wake 1-W T Design of wake adapted propeller  In order to achieve desired high propulsive efficiency and ensure favorable cavitation and acoustic characteristics of propeller, one has to design the propeller well adapted to the wake field behind ship hull.  Interaction between ship hull and propeller results in effective wake field on propeller that may differ considerably from nominal wake, which is normally measured during model E = 0.769 Effective wake: 1-W T tests.  At MARINTEK we employ a coupled viscous/potential method to extract the effective wake field and optimize propeller design, using our in-house propeller design and analysis software. In this coupled method, STAR-CCM+ performs as a viscous flow solver.

Analysis of propeller characteristics under extreme off-design conditions  These studies are relevant to the problems of low-speed maneuvering of ships, backing and crash-back situations.  Off-design propeller analysis involves extremely complex flows, where the blade back side performs as a pressure side, and the whole blade is stalled.  Extended domains of separated and re- circulated flows exist, giving rise to unsteady vortex shedding.  The example shown on this slide presents the comparsion between the experimental data and numerical predictions obtained with STAR-CCM+ (unsteady RANS method) for the B-series propeller operating in the entire 1st quadrant.

Investigations into scale effect on ducted propellers  Interaction between propeller and duct is a crucial mechanism behind scale effect.  The regions of blade tip clearance and duct T.E. are of particular importance.  Ducted propeller flow is most adequately solved in the unsteady formulation, by employing the Sliding Mesh method.  Scale effect depends significantly on the duct type, propeller geometry, and radial loading distribution towards blade tip, which complicates greatly the application of simplified engineering scaling methods.  Within the frameworks of the ongoing R&D project “PROPSCALE” we use STAR-CCM+ to quantify scale effect on ducted propellers of different types.

Studies on formation and development of blade vortices  The physical mechanisms associated with the formation and development of blade tip and leading edge vortices are still not investigated to a sufficient degree.  In particular, unsteady phenomena, such as vortex bursting and breaking- up, represent substantial interested from the point of view of propeller noise, erosion and induced pressure impulses.  In this example, we used an unsteady RANS method of STAR-CCM+ to study the behavior of the leading edge vortex that caused erosion on the blades of a pulling podded propeller operating at bollard condition.

2) Approaches to numerical modeling of ship-propeller interaction

Challenges associated with numerical modelling of ship-propeller interaction  Unsteady (time-dependent) nature of the problem due to the interaction between the rotating parts (propeller) and stationary parts (hull, appendages, rudder).  Presence of free surface of unknown geometry.  Flow turbulence of various scales that need appropriate modeling assumptions.  Scale effects, including those related to the presence of laminar and transient flow regimes in model scale.

Approaches and software employed in ship-propeller interaction simulations Approaches: 1) Iterative coupled viscous/potential method with Actuator Disk Hull – RANS, Propeller – Panel method or Lifting surface, Coupling – Actuator Disk (Circumferential-averaged volumetric momentum source model), Free surface – VOF. 2) Unsteady RANS method with simplified account for free surface effect Hull – RANS, Propeller – RANS (Sliding Mesh), Free surface – not included (symmetry plane – «double-body model»). 3) Fully unsteady RANS method with free surface Hull – RANS, Propeller – RANS (Sliding Mesh), Free surface – VOF. Software: RANS solver: STAR-CCM+ (CD-Adapco) Panel method solver: AKPA (MARINTEK, in-house propeller analysis program) Lifting surface solver: AKPD (MARINTEK, in-house propeller design program) Actuator Disk setup: ADM (MARINTEK, in-house)

Coupled method: Main principles Actuator disk model  Disk thickness: 0.01D . Constant loading along the disk axis.  Radial distribution of elemental thrust identical to realistic propeller calculated by PM – dT(r).  Equivalent, but not identical distributions of circulation and elemental torque -  (r) and dQ(r).  Circumferential averaged distribution of momentum sources (axial and tangential). Effective wake field  All-component wake field .  AD induced velocities are defined from an additional Open Water calculation with the AD, having the same dT(r) as the AD behind hull.  Velocities are sampled at the wake control section 0.1D upstream of propeller plane.

Unsteady RANS method: Main principles Hull-propeller interaction  Rotation motion of propeller region  Sliding interface mesh  Time-accurate 1st order,  t  2  of propeller revolution  Two-stage solution MRF+SM Turbulence *) SST k-  , All Y+ Treatment  (used routinely)  Other turbulence models Free surface *) DOF *) (RSM, DES – investigated)  VOF, 2nd Order, FlatVofWaves  Fixed position  Blended HRIC; Pure HRIC  2DOF (free sinkage and trim)  Time-accurate 1st order,  t=(0.005 ÷ 0.01) × L PP /V *) Also apply with the Coupled Method

Meshing considerations: Ship hull – (1) Coarse mesh: Hex trimmed mesh, (5 ÷ 7) prism layers, stretching factor (1.25 ÷ 1.35), 1.5 mio cells per half ship without appendages, 30<Y + <90.

Meshing considerations: Ship hull – (2) Free surface treatment  About 30 cells in vertical direction, 3 volumetric controls.  About 100 cells per wave length near ship hull, about 30 cells per wave length in the far field.  Wave damping at the Inlet, Outlet and Side boundaries; Damping length is chosen so that damping begins in the refinement zone.  The size of the domain in transverse direction is large enough to avoid intersection of the Kelvin’s wake with the side boundaries.

Meshing considerations: Propeller Fine mesh: Poly mesh, (10 ÷ 30) prism layers, stretching factor (1.1 ÷ 1.2), (1.3 ÷ 1.5) mio cells per blade passage, Y + <1. Coarse mesh: Tet mesh, no BL mesh, (0.3 ÷ 0.5) mio cells per blade passage, 30<Y + <250.

3) Validation example of the benchmark KCS container ship

Main particulars of ship and propeller Main particulars Model scale Length between PP L PP , [m] 7.2786 Maximum beam at B WL , [m] 1.019 WL Depth D, [m] 0.6013 Draft T, [m] 0.3418 S W , [m 2 ] KRISO container ship KCS Wetted surface area 9.4379 Block coefficient C B 0.6505 Midship section C M 0.9849 coefficent Coordinates of (x/L PP , y/L PP , (0.4825, 0.0, propeller center *) z/L PP ) -0.02913) *) Origin of coordinate system at CP, midship, WL; x - downstream Propeller elements Model scale Propeller diameter D P , [m] 0.25 Hub ratio d H /D P 0.18 Number of blades Z 5 KRISO Propeller KP505 Blade area ratio A E /A 0 0.8 Pitch ratio P(0.7R)/D 0.9967 Sections NACA66/a=0.8 Conditions Calm water, Fixed position and Free motion Without rudder Fr=V/(g*L PP ) 1/2 Froude number 0.26 Re=(V*L PP )/ ν 1.4*10 7 Reynolds number Ship speed V, [m/s] 2.19663 Propeller RPS *) n, [Hz] 9.5 *) Measured during self-propulsion tests

Resistance calculation: Ship Resistance – Influence of interface scheme Experiment with Rudder (KRISO) without Rudder (SRI) friction line Ct Cp Cf Ct Cp -residual Cf Cf0 (ITTC-57) 0.003557 0.003534 0.000689 0.002845 0.002832 Calculations with blended HRIC scheme Time step, interface scheme Cp Cv Ct dt=0.02 [s], blended HRIC 0.000711 0.002843 0.003554 dt=0.03 [s], blended HRIC 0.000726 0.002846 0.003572 dt=0.05 [s], blended HRIC 0.000756 0.002849 0.003605 Solution appears dependent on time step due to the Courant number limits in the blended HRIC scheme Calculations with pure HRIC scheme Time step, interface scheme Cp Cv Ct dt=0.01 [s], pure HRIC 0.000633 0.002840 0.003473 dt=0.02 [s], pure HRIC 0.000630 0.002842 0.003472 dt=0.03 [s], pure HRIC 0.000628 0.002842 0.003470 dt=0.04 [s], pure HRIC 0.000630 0.002842 0.003472 dt=0.05 [s], pure HRIC 0.000630 0.002842 0.003472 Solution is independent on time step *) SST k-  turbulence model is used in this exercise

Resistance calculation: Wave profiles

Resistance calculation: Pressure distribution on the hull