Particle Image Velocimetry Measurements of Buoyancy Induced Flow Through a Doorway
Rodney A. Bryant
Quantifying the ventilation available to an enclosure fire is an important step to understanding fire behavior. Accurate measurements of mass flow rate across an enclosure opening require a complete mapping of the velocity and density fields due to the three dimensional nature of vent flows. Conventional flow measurement methods in fire research consist of vertical arrays of thermocouples and differential pressure probes at the vent plane which are physically obtrusive and offer limited spatial sampling. A reduced scale analog of a full scale fire experiment was studied for the purpose of studying the potential use of Stereoscopic Particle Image Velocimetry, a laser based non-intrusive imaging technique, to measure fire induced flows through vents. The experiment was isothermal and modeled the convective transport by using a helium plume as the buoyant source. Stereoscopic PIV measurements were successfully demonstrated for a large scale flow field with planar image regions of 0.71 m x 0.62 m (l x h). Measurements of the complete velocity vector, vx,vy,vz, were performed and a full mapping of the velocity field in the region of the doorway was achieved. The vector field data displays the three dimensional structure of the flow through the doorway, revealing regions where the velocity component normal to the doorway plane may not completely dominate the velocity vector. A comparison of mass flow rate computations was consistent with doorway flow orifice coefficients, by demonstrating that mass flow rate will be over predicted by as much as 25% if computed using the velocity magnitude, which is representative of a vertical array of bi-directional probe measurements. The intermediate scale of the flow field was sufficient to test the performance of current PIV systems and to identify the requirements for conducting successful PIV measurements in a full-scale fire experiment.
Particle Image Velocimetry Measurements of Buoyancy Induced Flow Through a Doorway, NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online], https://doi.org/10.6028/NIST.IR.7252
(Accessed September 25, 2023)