Norsk Marinteknisk Forskningsinstitutt Numerical Modeling of Ship-Propeller Interaction under Self-Propulsion Condition Vladimir Krasilnikov Department of Ship Technology, MARINTEK Trondheim, Norway STAR Global Conference 2014 Vienna, Austria, March 17-19
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Norsk Marinteknisk Forskningsinstitutt
Numerical Modeling of Ship-Propeller Interaction under Self-Propulsion Condition
Vladimir KrasilnikovDepartment of Ship Technology, MARINTEK
Trondheim, Norway
STAR Global Conference 2014
Vienna, Austria, March 17-19
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
Nominal wake 1-WTN = 0.736
Effective wake: 1-WTE = 0.769
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 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
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.
Challenges associated with numerical modelling of ship-propeller interaction
Approaches:
1) Iterative coupled viscous/potential method with Actuator DiskHull – 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 effectHull – RANS, Propeller – RANS (Sliding Mesh), Free surface – not included (symmetry plane – «double-body model»).
*) Origin of coordinate system at CP, midship, WL; x -downstream
Propeller elements Model scalePropeller diameter DP, [m] 0.25Hub ratio dH/DP 0.18Number of blades Z 5Blade area ratio AE/A0 0.8Pitch ratio P(0.7R)/D 0.9967Sections NACA66/a=0.8
ConditionsCalm water, Fixed position and Free motionWithout rudderFroude number Fr=V/(g*LPP)1/2 0.26
Reynolds number Re=(V*LPP)/ν 1.4*107
Ship speed V, [m/s] 2.19663Propeller RPS *) n, [Hz] 9.5*) Measured during self-propulsion tests
KRISO container ship KCS
KRISO Propeller KP505
Main particulars of ship and propeller
Time step, interface scheme Cp Cv Ct
dt=0.01 [s], pure HRIC 0.000633 0.002840 0.003473dt=0.02 [s], pure HRIC 0.000630 0.002842 0.003472
dt=0.03 [s], pure HRIC 0.000628 0.002842 0.003470dt=0.04 [s], pure HRIC 0.000630 0.002842 0.003472
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
Resistance calculation: Ship Resistance – Influence of interface scheme
Calculations with blended HRIC scheme
Calculations with pure HRIC scheme
Experiment
Solution appears dependent on time step due to the Courant number limits in the blended HRIC scheme
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
Resistance calculation: Ship Resistance – Influence of turbulence model
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 dt=0.02 [s]
Turbulence model Cp Cv Ct
SST k-w 0.000711 0.002843 0.003554
Real k-e 0.000717 0.002853 0.003570RSM *) 0.000697 0.002972 0.003669
SST k-w + RSM *) 0.000703 0.002971 0.003674
*) RSM Model: Linear Pressure Strain, High-Re
Turbulence model Cp Cv CtSST k-w 0.000630 0.002842 0.003472
Real k-e 0.000636 0.002852 0.003488RSM *) 0.000618 0.002970 0.003588
Calculations with pure HRIC scheme, Time step dt=0.02 [s]
Resistance calculation: Nominal wake field
Influence of turbulence model. Symmetry of calculated wake field: Half
ship and full ship. Influence of the inclusion of a new region:
Propeller block and Actuator Disk block.
Objectives of the study
Resistance calculation: Free sinkage and trim, different Froude numbers
Oscillatory convergence is observed for all conditions.
At lower Fr, oscillations show larger amplitude, and levels of residuals are higher.
The presented results are obtained with blended HRIC, dt=0.02 [s]. Calculation done with pure HRIC reveal large oscillations and become unstable at lower Fr.
Observations
Calculation of open water propeller characteristics
Self-propulsion calculation: Ship resistance and propeller characteristics
Ct, S-P RPS KTB KQB
Coupled method 0.003991 9.55 0.1703 0.02942
, % +0.63 +0.53 +0.18 +2.15
Unsteady RANS method 0.003907 9.53 0.1650 0.02933
, % -1.48 +0.32 -2.94 +1.84
Experiment 0.003966 9.50 0.170 0.0288
Coupled methodBlended HRIC, dt=0.05 [s]; SST k-; 5 iterations between the RANS and panel method solvers.
Unsteady RANS method:MRF+SM; Pure HRIC and Blended HRIC *), dt=0.02 [s] at MRF stage, dt 2 at SM stage; SST k-; About 50 propeller revolutions are performed at the SM stage.
Calculation results at «ship point», SFC=30.3 [N] from model tests
*) Both the calculation with pure HRIC scheme and blended HRIC scheme result in very close predictions of resistance and propeller forces, since the pure HRIC scheme is used effectively at the SM stage due to small time step.
Self-propulsion calculation: Pressure distribution on the hull
*) Results obtained with Unsteady RANS method
Self-propulsion calculation: Velocity field downstream of propeller
4) Aspects of numerical modeling that
require closer attention
Pure HRIC Offers solution independent on time step, which is advantageous in self-propulsion simulations using realistic propeller.
Blended HRIC Shows more stable performance in simulations involving free motion.
What is the best practice for self-propulsion simulations with free motion?
VOF: Interface capturing scheme
Wetted transom flow and vortex separation
A small wetted area is predicted at the transom, in the vicinity of CP.
Wave elevation is over-predicted at the stern end, but agrees well with the measurements aft of the transom.
The flow in this region is influenced by vortex separation that occurs at the transom, both below and above the free surface.
Resolution of vortices in propulsor slipstream
With standard two-equation turbulence models the computed slipstream vortices are excessively diffusive, and they dissipate too soon downstream of propulsor.
Before making the final shift toward the use of LES and DES methods, one should explore the possibilities of improvement offered by: Anisotropic turbulence models (RSM); Vorticity confinement method; Curvature correction model.