Recent Advances in Modelling Wind Parks in STAR‐CCM+

Steve Evans

Agenda

• Introduction

– Company

– STAR-CCM+

• Wind engineering at CD-adapco

• STAR-CCM+ & EnviroWizard

– Developments for Offshore Simulation

CD-adapco: Engineering Success

3

We are a growing and successful engineering simulation company

• 20%+ growth in FY2011 global software sales

• $130m End User Spend in FY2011

• >560 employees in ~25 offices

• 40% of employees involved in Research and Development activities

• >9000 users worldwide

Our purpose is to ensure the customer’s success through the use of engineering simulation

• Enable & inspire innovation

• Reduce engineering time & costs

We provide successful engineering simulation solutions

• Software products like STAR-CCM+ that are accurate, efficient, and easy to use

• Flow, Thermal and Stress simulation in a single tool.

• Local dedicated support

• Engineering services: technology transfer, burst engineering resources, custom software tools

Our independence breeds engineering success

• Largest independent CAE/CFD provider

• Heavily invest in employees

• Continuously invest in development of new technology

Why our software technology? From our customers perspective

• A single workflow environment

– Integrated Flow, Thermal, Stress Process

– One tool to learn with all the major physics

– Allows easy toggle from one task to another

– “On the fly” solver setting change

– Streamlined and effective modelling

• Rapid pre-processing & design change

– Reduced man-hours on model prep

– Streamlined meshing for highly complex models

– Rapid design change analysis: Stop, change, start from last

• Client-Server

– Efficiency of large models over multiple cores

– Eliminate lag-time in transferring models to/from clusters to workstation

• Custom automation

– Design of Experiment

– Deploy best-practices to new users quickly

– Ensure consistency

Techn

ical V

alu

e

Wind Engineering with STAR-CCM+

• We have been working with our customers in the Wind Energy Business for the past 5 years.

• Today we have customers working

– Automated wind and site

– Automated blade design

– Offshore and ship engineering

– Code coupling (CFD to FE)

– Acoustics

STAR-CCM+ EnviroWizard

• The EnviroWizard is a GUI driven work process allowing quick & efficient setup of investigations of Wind & Site problems using STAR-CCM+

• Workflow process

– Terrain import

– Mesh Creation

– Boundary Conditions

– Polars (N directions)

– Post processing

» Quantitative

Wake Interactions

• Modelling the turbine interaction problem can generally be split into two problems

– Near Wake Effects

» 3D & tip effects, stall

- High fidelity models BEM/CFD required

– Far wake (Wind Park Level) including

» Wake interaction, turbulence & terrain

- Lower fidelity model such as actuator discs can be used

• EnviroWizard allows the User to investigate wake interactions

– Automatic setup of mesh and actuator functions

NASA AMES Wind Tunnel

Wake Interactions

• Each turbine is modelled individually as a momentum source.

– Torque

– Thrust

» User can choose

– Uin is area averaged velocity upstream of the disc

– Embedded meshing

» Hexahedral dominant mesh in main region

» Polyhedral disc & buffer region

270 degrees, flow aligned grid

Uin determined here

Buffer Region

Disc

EnviroWizard Developments

• While this automatic wake methodology works, the setup requires remeshing for each wind direction.

• In STAR-CCM+ 7.02 (end Feb 2012), CD-adapco will release a version containing the Overset method,

– This has the possibility to simplify the array problem

» No remesh.

» Just change the wind direction and disc orientation.

• The EnviroWizard will be released at the same time incorporating this functionality.

Overset Methodology

• Cells are marked according to three types:

– active, inactive, and acceptor.

• Active cells » regular discretized equations are solved.

» Donor for the interpolation.

• Inactive cells

– no equation is solved – they are temporarily de-activated.

– Need to be surrounded by acceptor cells.

• Acceptor cells

– discretized equations are replaced by interpolation equations which express cell-centre value of a variable as a linear combination of values at another grid.

Overset Methodology

Overset Validation

• Steady State Re=50 cross flow cylinder, 24K elements

Steady State Pressure

Steady State Velocity

Continuity Residuals Red – overset Green – no overset

Overset Validation

• Transient Re=200 cross flow cylinder, 24K elements

Time 0 – 150s

Y F

orc

e

Overset Features

• Release features for v702 (end Feb 2012)

– Any number of overlaps, restricted to:

» Not overlapping each other

» Not overlapping any solid body or exit background mesh

– Physics / Solver

» Steady, moving, or sliding grid.

» Parallel

» VOF, cavitation etc.

» Not particle tracking, liquid film

EnviroWizard with Overset

• New option in the Disc Models

– Setup of N turbines in array is performed with the Wizard.

• Test against a known case, Hornsref

Overset disc

The author wishes to acknowledge Elkraft who provided this production data and the owners of the array, Dong Energy and Vattenfall.

EnviroWizard with Overset

• Computational requirements

– Approximate timings for 5.9M cells

» 1 background mesh with 80 overset regions

– Test machine 2*4 core Intel Xeon X5560 2.8GHz

– Setup & mesh

» 15m

– Solver

» elapsed time on 8 cpus = 38 s/iter

– Peak memory (coupled solver)

» ~40 G

Convergence

EnviroWizard with Overset

6 m/s case

EnviroWizard with Overset

4

4,5

5

5,5

6

6,5

1 2 3 4 5 6 7 8

Upwind Nearly Neutral

STAR-CCM+ Overset

6 m/s case

Turbine number

Velo

city

Conclusions

• STAR-CCM+ is an open toolbox for simulating many aspects of wind engineering.

• Here we demonstrate a new feature of STAR-CCM+ v702 which has the possibility to greatly simplify the setup and calculation of offshore arrays using the overset method.