Dynamic Flow Simulator

The DFS is used to determine ultimate wind uplift capacities of discontinuous roofing systems (such as tiles, asphalt- or metal- shingle systems), for which the uplift capacity is dependent on the geometric profile (high-profile versus near-flat profile) and effectiveness of air seals between rows of tiles. The unique features of the DFS include the maximum velocity at the test section – approximately 100 m/s – and the ability to replicate up to a 2 Hz waveforms. The DFS was designed to test full-scale roof specimens up to 2 m wide by m by yy m. The tile geometry affects the air leakage through the system and therefore the overall uplift loads generated. The wind field generated in a vertical plane above the shingle test specimen represents the variation of near-surface wind flowing above a roof.

Capabilities and Principle of Operation DFS air supply is provided by the same system that is used to power the MAWLS. Valves in the ducting system are adjusted to direct air flow into the DFS test section, which is 2.1 m wide by 2.6 m long. The height of the section increases alongwind to regain static pressure lost by friction to achieve a zero longitudinal pressure gradient in the test section. Before air enters the test section it travels through a settling chamber consisting of a wide-angle diffuser, turbulence screens, honeycomb (68% porosity), and a duct contraction. The settling chamber mitigates undesired fine-scale turbulence and improves flow uniformity across the duct cross-section. The duct contraction causes the wind to accelerate to its target velocity through the test section. Test specimens inside the DFS are subjected to the mean and turbulent components of near-roof wind, providing a unique tool to accurately measure the wind load and resistance of discontinuous roofing systems.

Instrumentation

  • Scanivalve Corp. 512 Channel Pressure Scanning System
  • [2 units] ATI Industrial Automation Nano25 6-Axis Load Cell
  • [4 units] Turbulent Flow Instrumentation Cobra Probe
  • Phantom V5.2C High Speed Camera
  • [2 units] GoPro Hero3+ Cameras

Calibration

Full-scale wind velocity data collected from Hurricane Katrina were resampled at four intensity levels with mean wind velocity = 15, 25, 35 and 45 m/s. The figure below compares the measured velocity to the command signal. The solid black line represents the input (or “command”) velocity signal, and the dash-dot gray line describes the measured (or “response”) signal. It can be seen that the simulator follows the commanded signal well. The table lists the statistics of the input and measured wind velocity time histories. It is seen that the means, coefficients of variation, kurtosis values, maximum values agree well. The skewness values match well for levels 1 and 2, but have a difference of 0.26 and 0.27 respectively for levels 3 and 4.

 

  Level 1
Command
Level 1
Measured
Level 2
Command
Level 2
Measured
Level 3
Command
Level 3
Measured
Level 4
Command
Level 4
Measured
Mean 15.8 14.6 25.7 25.3 35.7 36.3 46.6 47.7
CoV 0.30 0.33 0.25 0.28 0.22 0.24 0.21 0.21
Skewness 0.30 0.33 0.29 0.27 0.29 0.03 0.28 0.01
Kurtosis 2.87 3.11 2.84 2.53 2.84 2.59 2.82 2.76
Minimum 3.99 -3.50 10.0 6.40 16.1 10.6 22.1 15.3
Maximum 34.2 34.4 50.2 49.4 66.3 64.6 82.4 79.8