cfd for aerodynamics of fast ships volker bertram l.
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CFD for Aerodynamics of Fast Ships Volker Bertram. Scenario - what, why, etc. Aerodynamic flow around a ship superstructure is important in many ways: Exhaust dispersal Ventilation of occupied spaces Wind forces, especially for maneuvering

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scenario what why etc
Scenario - what, why, etc.
  • Aerodynamic flow around a ship superstructure is important in many ways:
    • Exhaust dispersal
    • Ventilation of occupied spaces
    • Wind forces, especially for maneuvering
    • Special operational conditions - helicopter landing, etc.
  • Used to make design & operational decisions
wind tunnel proven tool
Wind tunnel proven tool

This information now predominantly from wind tunnel tests

Wind tunnel proven tool to provide useful information about the airflow.

aero cfd an alternative now
Aero CFD: An alternative now!
  • Aerodynamics CFD effective in other engineering fields:
  • aerospace
  • automotive
  • civil engineering
  • Advantages:
  • All information available at any time
  • More precise control over what is viewed
  • More details are possible
  • Full scale (but still idealized...)
  • Non-intrusive
cfd for ship aerodynamics now a topic
CFD for ship aerodynamics now a topic
  • Problem difficult due to various factors:
    • Grid generation very difficult
    • Large grid cell count
    • Complex physics
  • Recent progress addresses these issues:
    • Unstructured, more robust solvers
    • Improved, automatic grid generation tools
    • Advanced numerical modeling techniques
    • Affordable parallel computing
several applications in last years
Several applications in last years
  • DMI
  • Sirehna
  • Marintek
  • NRL
  • JJMA
  • Stanford
  • KRISO
  • ... (?)

DMI

JJMA

NRL

Sirehna

tools and methods used
Tools and Methods Used

Typical geometry imported from IGES format

Unstructured, tetrahedral grids generated using ICEM-CFD, cell count of up to 5 million cells

Calculations with Comet on a parallel PC cluster

baffle elements tested
Baffle Elements Tested

model global effect of replacing filigree structures

by semi-permeable cell boundaries

cell count for a 2D case

22 000 cells

6 000 cells

baffle elements disappointed
Baffle elements disappointed

k and |v| for mast

geometric model

Assorted baffle parameters

simple block does the trick
Simple block does the trick

k and |v| for mast

geometric model

Simple block

application to fast ferry
Application to fast ferry

Superfast VI, HDW, 29 kn

IGES file from yard too detailed: several weeks work

to downstrip

model tests performed at ifs wind tunnel
Model tests performed at IFS wind tunnel

Physical model (1:150) in wind tunnel

slide18

Some similarity laws always violated

ratio of velocities

ratio of mass flux

ratio of momentum flux

Reynolds number of the inflow

Reynolds number of the jet

Froude number ofthe jet

geometric similarity

They cannot be fulfilled all at the same time!

parameter studies
Parameter studies

exhaust gas temperature 300°C

model test parameters

full scale Rn

inviscous computation

visualisation of different quantities
Visualisation of different quantities

pressure distribution (30°)

stream lines (0°)

turbulent kinetic energy k (0°)

forces ok for small to medium angles
Forces OK for small-to-medium angles

Drag

Roll

moment

Side

force

Differences for large oblique angles

attributed to flow separation

insufficiently captured by turbulence model

application to fast ses
Application to fast SES

AGNES 200, French SES, 40 kn

First step:

Create IGES

description

grid topology allows easy re gridding
Grid topology allows easy re-gridding

Inner cylinder in outer block

Matching every 5°

2.9 million cells

strongly 3 d flow
Strongly 3-d flow

streamlines =180°

5 cm higher

features similar for 170
Features similar for 170°

streamlines =170°

less complex foil flow for for 150
Less complex “foil” flow for for 150°

Flow follows

low-pressure

side of SES

streamlines =150°

Streamlines return to original

direction further downstream

flow strongly 3 dimensional
Flow strongly 3-dimensional

Virtual Reality may help understanding the flow

virtual reality comes in many shapes
Virtual Reality comes in many shapes

Poor man’s VR suffices!

Sources: VRL, Univ. Of Michigan; VRCA RWTH Aachen

cave head-gear PC

VRML

what is vrml
What is VRML?

VRML = Virtual Reality Modeling Language

  • 3D file interchange format
  • 3D analogue to HTML
  • ISO standard
steps creating a cfd vrml model
Steps creating a CFD VRML model
  • Study experience of others

VRL, Univ. of Michigan

INSEAN INSEAN+TUHH TUHH

slide33

Steps creating a CFD VRML model

  • Study experience of others
  • Export geometry data from RANSE solver
  • Downsize geometry

Direct export:

43000 polygons

2810 KByte

slide34

Steps creating a CFD VRML model

  • Study experience of others
  • Export geometry data from RANSE solver
  • Downsize geometry

Direct export:

43000 polygons

2810 KByte

After merging:

900 polygons

130 KByte

steps creating a cfd vrml model35
Steps creating a CFD VRML model
  • Build VRML geometry model
  • Process and downsize flow data
  • Add flow data to VRML model
  • Add interaction to VRML model

Interactive

selection

Interactive

high-lighting

pressures use colour vrml interpolation
Pressures use colour VRML interpolation

Work continues:

  • Refine algorithm to downsize model
conclusions
Conclusions
  • CFD offers more insight than wind tunnel
  • Further work required for validation
  • Wind tunnel may be too optimistic for smoke tracing
  • VRML suitable for post-processing