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Influence of wind on receivers for solar power towers

OpenFOAM user conference 2014 Institute of Solar Research, German Aerospace Center Robert Flesch

> Influence of wind on receivers for solar power towers > Robert Flesch • 2014-10-08_OFUC_Flesch_WindSolarReceiver > 2014/10/08 DLR.de • Chart 1

German Aerospace Center (DLR)

> Influence of wind on receivers for solar power towers > Robert Flesch • 2014-10-08_OFUC_Flesch_WindSolarReceiver > 2014/10/08 DLR.de • Chart 2

Aeronautics Space

Transport Energy

Outline

> Influence of wind on receivers for solar power towers > Robert Flesch • 2014-10-08_OFUC_Flesch_WindSolarReceiver > 2014/10/08 DLR.de • Chart 3

1. Introduction

2. Experiment

5. Validation 3. CFD setup

4. CFX comparison 6. Heat loss mechanism

Cavity Receiver for Solar Power Towers

> Influence of wind on receivers for solar power towers > Robert Flesch • 2014-10-08_OFUC_Flesch_WindSolarReceiver > 2014/10/08 DLR.de • Chart 4

Questions Approach

Aim and Approach

(1) What influence has wind on the losses?

• Different receiver inclinations

• Different wind directions

• Different wind speeds

(2) Can the influence of wind be analyzed with CFD?

• RANS approach

(1) Experiment

• Wind tunnel experiment

• Similarity approach

(2) CFD simulations

• Wind tunnel setup

> Influence of wind on receivers for solar power towers > Robert Flesch • 2014-10-08_OFUC_Flesch_WindSolarReceiver > 2014/10/08 DLR.de • Chart 5

Experimental Approach

• Similarity – main dimensionless numbers • Reynolds number Re = 𝑢∞ 𝐷𝑖 𝜌

𝜇ref

• Grashof number Gr = 𝑔 𝐷𝑖3𝜌2

𝜇ref2

Tw−T∞𝑇ref

> Influence of wind on receivers for solar power towers > Robert Flesch • 2014-10-08_OFUC_Flesch_WindSolarReceiver > 2014/10/08 DLR.de • Chart 6

• Cryogenic wind tunnel cologne • Ambient temperature -173°C • Scaling factor 3.5

Inclination Angle ϕ

Reducing the ambient temperature

Upscaling

Experimental Approach Local heat transfer

> Influence of wind on receivers for solar power towers > Robert Flesch • 2014-10-08_OFUC_Flesch_WindSolarReceiver > 2014/10/08 DLR.de • Chart 7

Zone 0 Zone 1 Zone 2 Zone 3 Zone4

Benefits using OpenFOAM Concerns about using OpenFOAM

CFD approach Why using OpenFOAM?

• License costs

• High computational effort for heat loss simulation

• Open source code

• Expandability

• Clarity concerning the used models

• Training period

• Lack of documentation

• Reliability (Results)

• Prevalence

> Influence of wind on receivers for solar power towers > Robert Flesch • 2014-10-08_OFUC_Flesch_WindSolarReceiver > 2014/10/08 DLR.de • Chart 8

CFD approach Model setup

• Mesh creation

• ANSYS ICEM

• Appr. 3.5∙106 Elements

• Environment

• Wind tunnel setup

• Nitrogen -173°C

• Ideal Gas

• Janaf thermo

• Polynomial transport

> Influence of wind on receivers for solar power towers > Robert Flesch • 2014-10-08_OFUC_Flesch_WindSolarReceiver > 2014/10/08 DLR.de • Chart 9

• Turbulence model

• k-ω-SST

• Prt=0.85

• Solver

• OpenFOAM 2.3.0

• buoyantPimpleFoam

CFD approach Boundary conditions I

> Influence of wind on receivers for solar power towers > Robert Flesch • 2014-10-08_OFUC_Flesch_WindSolarReceiver > 2014/10/08 DLR.de • Chart 10

Inner walls

mut mutLowReWallFunction;

k → 0

omega compressible::omegaWallFunction;

alphat calculated;

T fixedValue;

Outer walls

mut mutkWallFunction;

k compressible::kqRWallFunction;

omega compressible::omegaWallFunction;

alphat calculated;

T zeroGradient;

CFD approach Boundary conditions II

> Influence of wind on receivers for solar power towers > Robert Flesch • 2014-10-08_OFUC_Flesch_WindSolarReceiver > 2014/10/08 DLR.de • Chart 11

Inlet (natural convection) U pressureInletOutletVelocity p_rgh totalPressure T inletOutlet

Outer walls

mut mutkWallFunction;

k compressible::kqRWallFunction;

omega compressible::omegaWallFunction;

alphat calculated;

T FixedValue T∞

Inlet (forced convection) U fixedValue p_rgh zeroGradient T fixedValue

CFX Nu = 305

OpenFOAM Nu = 308

Results CFX comparison

> Influence of wind on receivers for solar power towers > Robert Flesch • 2014-10-08_OFUC_Flesch_WindSolarReceiver > 2014/10/08 DLR.de • Chart 12

• Highest velocity 5 m/s • Horizontal receiver • Head-on wind • Same fluid property functions

Validation

DLR.de • Chart 13

ϕ

> Influence of wind on receivers for solar power towers > Robert Flesch • 2014-10-08_OFUC_Flesch_WindSolarReceiver > 2014/10/08

ϕ ϕ

Validation

DLR.de • Chart 14

ϕ

> Influence of wind on receivers for solar power towers > Robert Flesch • 2014-10-08_OFUC_Flesch_WindSolarReceiver > 2014/10/08

ϕ ϕ

Validation

DLR.de • Chart 15

ϕ

> Influence of wind on receivers for solar power towers > Robert Flesch • 2014-10-08_OFUC_Flesch_WindSolarReceiver > 2014/10/08

ϕ ϕ

Validation

DLR.de • Chart 16

ϕ

> Influence of wind on receivers for solar power towers > Robert Flesch • 2014-10-08_OFUC_Flesch_WindSolarReceiver > 2014/10/08

ϕ ϕ

Validation Loss Mechanism

> Influence of wind on receivers for solar power towers > Robert Flesch • 2014-10-08_OFUC_Flesch_WindSolarReceiver > 2014/10/08 DLR.de • Chart 17

Re2

Gr = 0 Re2

Gr = 1,29 Re2

Gr = 3,59

Experiment CFD Experiment CFD Experiment CFD

Zone 0

Zone 1

Zone 2

Zone 3

Zone 4

Validation Loss Mechanism

> Influence of wind on receivers for solar power towers > Robert Flesch • 2014-10-08_OFUC_Flesch_WindSolarReceiver > 2014/10/08 DLR.de • Chart 18

Re2

Gr = 0 Re2

Gr = 1,29 Re2

Gr = 3,59

Experiment CFD Experiment CFD Experiment CFD

Zone 0

Zone 1

Zone 2

Zone 3

Zone 4

Simulation Experiment

Validation Model errors

> Influence of wind on receivers for solar power towers > Robert Flesch • 2014-10-08_OFUC_Flesch_WindSolarReceiver > 2014/10/08 DLR.de • Chart 19

• Constant wall temperature

• Constant heat flux in zones

• Deviation in cases of nonuniform heat transfer

• No conduction

• Conduction in cylinder and through insulation

• Aperture is adiabatic

• Aperture is not adiabatic

Summary Outlook

Summary and Outlook

• Influence of wind • horizontal receivers → small influence • increasing inclination angle → increasing influence

• CFD simulations • Capable to predict the changes due to wind

• Absolute values are slightly underpredicted

• OpenFOAM • Powerful CFD tool • Improvable documentation

• Analysis of reduction strategies using OpenFOAM

• Prospective use of OpenFOAM in solar research

> Influence of wind on receivers for solar power towers > Robert Flesch • 2014-10-08_OFUC_Flesch_WindSolarReceiver > 2014/10/08 DLR.de • Chart 20

Thank you for your attention! Questions? Project Start-SF contract 323-2010-006

Backup

> Influence of wind on receivers for solar power towers > Robert Flesch • 2014-10-08_OFUC_Flesch_WindSolarReceiver > 2014/10/08 DLR.de • Chart 21

Validation

DLR.de • Chart 22

ϕ

> Influence of wind on receivers for solar power towers > Robert Flesch • 2014-10-08_OFUC_Flesch_WindSolarReceiver > 2014/10/08

ϕ ϕ

Turbulent heat transfer

> Influence of wind on receivers for solar power towers > Robert Flesch • 2014-10-08_OFUC_Flesch_WindSolarReceiver > 2014/10/08 DLR.de • Chart 23