Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Engineering Science

Program

Civil and Environmental Engineering

Supervisor

Kopp, Gregory A.

Abstract

Wind effects on buildings are commonly studied by testing 3D printed building models in a wind tunnel. A challenge with 3D printing is that the edges of these models may not be perfectly sharp, but rounded with a radius of curvature, R. It is well known that when edges are significantly rounded, the aerodynamics of the building can be altered (Robertson, 1991; Mahmood 2011), leading to inaccurate predictions of full-scale surface pressures and wind loads. However, there is presently no guidance on model edge radii prescribed in wind tunnel testing standards such as ASCE 49-12. The objective of the present study is to define a practical limit for edge curvature, beyond which, separating flow behaviour is no-longer representative of flow around a sharp-edged bluff body.

To investigate the effect of edge radii, a wind tunnel study was conducted on a generic low-rise building. Models of the building were constructed in four scales (1:200, 1:100, 1:50 and 1:25) and with five non-dimensional radii, R/H, where H is the model height. In total, twenty model configurations were tested in similar upstream flow conditions. It was found that pressure coefficients in regions of separated flow were most sensitive to changes in R/H. Changes in the pressure distributions with R/H suggest that the increased curvature weakens and suppresses the vortices near model edges responsible for severe suctions. These changes in the pressure distributions in these regions lead to changes in area-averaged pressure coefficients and overall uplift coefficients.

The change in pressure distributions appeared to be a continuous function of R/H. As a result, differences in the pressure distributions may continue to appear as R/H continues to decrease and, thus, it is suggested the edges of wind tunnel ought to be as sharp as possible. However, within the limitations of measurement uncertainty in the current experimental setup, it was determined that discrepancies in pressure distributions may continue to be discernable up to R/H =1.3%. As a result, it is proposed that edge radii of wind tunnel models should not exceed R/H = 1.3% to ensure similarity of model-scale and full-scale results.

Summary for Lay Audience

Wind effects on buildings are commonly studied by testing scaled, 3D printed building models in a wind tunnel. As the wind tunnel operates, pressure taps across the model surfaces measure surface pressures which are used to predict full-scale wind loads. A challenge with 3D printed models is that the edges may not be perfectly sharp, but rounded with a radius of curvature, R. It is well known that when edges are significantly rounded, the aerodynamics of the building can be altered (Robertson, 1991; Mahmood 2011), leading to inaccurate predictions of full-scale wind loads. However, there is presently no guidance on model edge radii prescribed in wind tunnel testing standards such as ASCE 49-12. The objective of the present study is to define a practical limit for edge curvature, beyond which, the aerodynamics and predicted wind loads have significantly changed.

To investigate the effect of edge radii, a wind tunnel study was conducted on a generic low-rise building. Models of the building were constructed in four scales (1:200, 1:100, 1:50 and 1:25), each with five non-dimensional radii, R/H, where H is the model height. In total, twenty model configurations were tested. It was found that surface pressures in regions near model edges are most sensitive to changes in R/H. These changes in the surface pressures subsequently lead to discrepancies in the predicted wind loads.

The change in surface pressures appear to be a continuous function of R/H. As a result, differences in the pressure distributions may continue to appear as continues to decrease and, thus, it is suggested the edges of wind tunnel ought to be as sharp as possible. However, within the limitations of measurement uncertainty in the current experimental setup, it was determined that discrepancies in pressure distributions may continue to be discernable up to R/H =1.3%. As a result, it is proposed that edge radii of wind tunnel models should not exceed R/H = 1.3% to ensure similarity of model-scale and full-scale results.

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

Share

COinS