EXPERIMENTAL & NUMERICAL INVESTIGATION OF WIND LOADS ON ROOFS

FOR VARIOUS GEOMETRIES

İsmail EKMEKÇİ , Mustafa ATMACA* and Hakan Soyhan

The University of Sakarya, Engineering Faculty, Sakarya, Turkey

* Marmara University,Technical Education Faculty, İstanbul,Turkey

• Background and Problem Statement• Goals and Requirements• Wind Tunnel and Measurements• Experimental Roof Setup and Measurements• Model and Calculation Method• Experimental wind pressure coefficients• Numerical wind pressure coefficients• Comparison of Experimental & Numerical Results• Conclusions• Future Work

Outline

Wind Tunnel

1- Inlet part, 2- turbulence regulating chamber, 3- collector, 4- Section area, 5- Diffuser Adapter 6- Diffuser, 7- Outlet chamber, 8- Fan connection, 9- Fan cabin,

10- Fan, 11- Tunnel chassis, 12- Tunnel carrying wheel, 13- Velocity control unit, 14- Pitot tub, 15- Manometer, 16- Temperature probe, 17- Computer 18- Hot wire anemometer unit, 19- Oscilloscope,

20- Table, 21-Roof model, 22- Differential pressure sensor 23-Interface console 24- Wattmeter 25-Interface

Experimental Roof Setup and Measurements

Dimensions of the Roof Model Measurement Points

Calculation Method for Measured Data

• Dimensionless pressure coefficients (Cp) [3] :

• Mean Wind Pressure (Pmean) and mean wind pressure coefficients ( ) :

2

0

21V

PPCP

n

ii

n

iii

mean

A

APP

1

1

n

ii

n

iii

mean,p

A

ACC

1

1

mean,pC

Numerical Calculations

Effects of Mesh refinement in the 3-D simulations

Mesh ClassMaximum

Number of NodsMaximum Number

of ElementsMean Relative Error of the Cp

Values %

A 4812 23668 40,18

B 5813 29538 33,46

C 6945 35574 20,45

D 8689 45512 8,32

E 11761 63160 10,22

Effects of Mesh refinement on the Mean Error of the Cp Values

Effects of different turbulence models on the Pressure distribution(3-D simulations)

Numerical Calculations

Cross section computational domain

Experimental wind pressure coefficients of α=10o roof slope for several wind directions

Φ=0o Φ=30o

Φ=60o Φ=90o

Experimental wind pressure coefficients of α=20o roof slope for several wind directions

Φ=0o Φ=30o

Φ=60o Φ=90o

Experimental wind pressure coefficients of α=30o roof slope for several wind directions

Φ=0o Φ=30o

Φ=60o Φ=90o

Numerical wind pressure coefficients of α=10o roof slope for several wind directions

Φ=0o Φ=30o

Φ=60o Φ=90o

Numerical wind pressure coefficients of α=20o roof slope for several wind directions

Φ=0o Φ=30o

Φ=60o Φ=90o

Numerical wind pressure coefficients of α=30o roof slope for several wind directions

Φ=0o Φ=30o

Φ=60o Φ=90o

Table1. Comparison of Experimental and Numerical Results for Mean Pressure Coefficients

Mean Pressure Coefficients (z/d=0,5) Roof Angle

Φ α =10o α =20o α =30o Exp. Num. %Ratio Exp. Num. %Ratio Exp. Num. %Ratio

Φ=0o -0,65 -0,66 0,44 -0,46 -0,64 17,66 -0,33 -0,34 5,05

Φ=30o -0,52 -0,59 13,63 -0,43 -0,54 11,16 -0,42 -0,58 36,02

Φ=60o -0,72 -0,80 11,84 -0,40 -0,42 2,31 -0,42 -0,46 10,31

Φ=90o -0,29 -0,27 7,13 -0,68 -0,67 1,37 -0,26 -0,26 0,96

Comparison of Experimental and Numerical Results for Mean Pressure Coefficients

CONCLUSIONS - I

•Although it is obtained convenient pressure coefficient (Cp) values between experimental measurements and numerical computations, there are some inconveniences at some points. These deviations mostly occurred at roof corner points and back surfaces. Reasons for those differences are grid structure, mesh dimension, sample space dimension, insufficiency of selected turbulence model and could not making experimentally sensitive measures at these points.

•In numerical computation initially the effect of mesh structure is investigated.

•In numerical computations to investigate the effect of turbulence model 6, turbulence models (k-ε, RNG, Grimaji, Zero-equation, New k-ε, Shi-Zhu-Lumley) are tested at ANSYS-Flotron. Zero-equation turbulence model gives more accurate results comparing to other turbulence models. Hence Zero-equation model is used at all numerical computations.

• For 100 roof slope critical suction pressure coefficients are obtained for 00 and 300 wind directions at x/s=0,1 and x/s=0,5, for 600 and 900 wind directions at x/s=0,5. For 200 and 300 roofs slope critical pressure coefficients are obtained for 00, 300, 600 and 900 wind directions at x/s=0,5.

• For 100, 200 and 300 roofs slope, at 900 wind direction and at z/d=0.16, 0.33, 0.5, 0.66 suction pressure coefficients are observed smaller than other wind directions.

• For 100, 200 and 300 roofs slope at 600 and 900 wind directions maximum suction pressure coefficients have been obtained at z/d=0,83.

• For 300 roof slope at 00, 300 and 600 wind directions, positive pressure coefficients have been obtained between x/s=0-0,4.

CONCLUSIONS - II