Wind tunnel setup

First, given that overhang effectiveness is calculated and quantified based on field measurement on Vancouver Building, results should be generalized for similar mid-rise building geometries located in similar terrain. To fulfill this objective wind velocity near the Vancouver building east facade and Fredericton south-west façade that have almost similar geometry has been measured and normalized velocities has been compared. Later, the effect of overhang on wind flow deflection and wind velocity reduction near the mentioned facades has been studied by adding 0.6 cm (1.2 m) overhang on the rooftop of 1:200 scale model of both test buildings.

In Fredericton test building, the weather station is installed on the main roof with enough distance from the mechanical room. The height of the anemometer is 4.5m above the main roof, which is comparable to the height of the mechanical room. The second objective is to confirm whether the presence of the mechanical roof has an influence on the wind flow at the anemometer location. The wind velocity has been measured at the place of anemometer of Fredericton down scaled model with and without presence of mechanical room on the model. Prior to the studies, a suburban exposure has been created using roughness elements and a suburban exposure of south-west facades of Fredericton building has been verified.

3.2.1. Concordia Atmospheric Boundary Wind Tunnel

Concordia University’s atmospheric boundary-layer wind tunnel is located in the Building Aerodynamics lab of the Engineering, Computer Science and Visual Arts Integrated Complex at the Sir George Williams campus. It is an open-circuit blow down wind tunnel with a centrifugal blower and a rectangular cross-section. The tunnel has a test section 12.20 m long, 1.80 m wide and has an adjustable suspended roof with a minimum and maximum height of 1.40 m and 1.80 m, respectively. The wind tunnel is equipped with a 1.21 m diameter turntable downstream of the test section (Chiu 2016).

A MARK HOT double inlet centrifugal blower with a capacity of 40 m³/s at a static pressure of 4 cm of water is capable of producing a maximum wind velocity of 14 m/s. The velocity distribution in an empty tunnel is approximately symmetric with respect to the vertical axis passing through the center of the turntable. Measurements show that there is a ±4% deviation from the

32 mean velocity below 250 mm height (Stathopoulos 1984). A schematic of the wind tunnel is shown in APPENDIX A.

3.2.2. Exposure and Model

The model of two study buildings (Vancouver and Fredericton) have been tested in the wind tunnel. As both buildings are located in a suburban environment, a suburban exposure is simulated in the wind tunnel. Similar to the experiment conducted by Chiu (Chiu 2016), a mixture of roughness elements have been placed along the length of the test section of the tunnel to obtain a similar exposure with the right mean speed exponent for suburban terrain. The roof of the wind tunnel was adjusted along the length of the test section to satisfy the condition of zero longitudinal pressure gradient for a suburban exposure. The blower was set to the maximum speed.

Figure 3.4 - Wind tunnel exposure simulation, Suburban terrain

3.2.3. Test Buildings Model

For the first objective, a 1:200 scale of stand-alone models of Vancouver and Fredericton building was placed in ABL wind tunnel. Due to high wind velocity in wind tunnel, the effect of 1.2 m overhang was not evident at the measurement points of 1:400 model.

33 Each model was fabricated of plywood and placed in the middle of turning table. The wind velocity was measured at the distance of 14 mm from the façade due to the profile of Cobra probe and size of the overhang added to the models, 6 mm, making sure the velocity is measured at the similar points with and without overhang. The measurement grids over the facades are mainly defined based on the location of WDR gauges on the Vancouver building. For comparison purposes an almost similar grid is defined for Fredericton model. In total the wind velocity is measured at 29 points and 52 points near Vancouver and Fredericton model respectively. Dimensions of 1:200 scale models and location of measuring points of each test building is shown in Figure 3.5 and Figure 3.6.

(a)

(b)

Figure 3.5 - East elevation (a) and top view (b) of the Cassiar building model with 1.2 m overhang (scale 1:200). The measurement points near the east facade are shown in addition to the wind monitor location. All values are in cm.

34 (a)

(b)

Figure 3.6 - South-west elevation (a) and top view (b) of the McLeod House building model with 1.2 m overhang (scale 1:200). The measurement points near the south-west facade are shown in addition to the wind monitor location. All values are in cm.

For the second objective, a 1:400 scale model of the Fredericton building and its surroundings within a 200 m radius have been fabricated and placed in an ABL wind tunnel. The 1:400 scale was selected based on the surroundings and successful simulations at this scale of the most important variables of the atmospheric boundary layer under strong wind conditions, carried out in this wind tunnel (Stathopoulos, 1984). The wind velocity was measured at the place of anemometer

35 for eight wind directions with 45 degrees interval with and without the mechanical room, as shown in Figure 3.7. The same experiment was repeated for the 1:400 and 1:200 standalone models of Fredericton building for comparison purposes.

(a) (b)

Figure 3.7 - McLeod House model for wind tunnel experiment, (a) 1:400 model with surroundings, (b) 1:200 model without surroundings

3.2.4. Wind Velocity Measurement

To measure the velocities in the wind tunnel, a Series 100 Cobra Probe was used. The Cobra Probe is a multi-hole pressure probe that provides dynamic, 3-component velocity and local static pressure measurements in real-time. The Probe is capable of a linear frequency response from 0 Hz to more than 2 kHz and is available in various ranges for use between 2 m/s and 100 m/s (Turbulent Flow Instrumentation, 2011). Also, the angles between velocity vectors is provided which is used to determine the flow direction near the façade. Yaw angle can be defined as the azimuth and the pitch is the angle between the flow velocity vector and the XY plane, Figure 3.8.

Figure 3.8 - (a) Flow axis system with respect to the Probe head, (b) Positive flow pitch and yaw angels {Formatting Citation}

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