Particle Image Velocimetry Measurements of Buoyancy Induced Flow Through a Doorway.
Particle Image Velocimetry Measurements of Buoyancy
Induced Flow Through a Doorway.
Bryant, R. A.
NISTIR 7252; 71 p. September 2005.
doorways; vents; experiments; uncertainity; ventilation;
velocity; large scale fire tests; mass flow; gas
density; flow visualization; particle image velocimetry
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 using the velocity component
normal to the opening, vx, and the velocity magnitude,
demonstrated that mass flow rate will be over predicted
by as much as 25% if computed using the velocity
magnitude. Velocity magnitude is representative of
bi-directional probe measurements and the over
prediction is consistent with the use of doorway flow
orifice coefficients to correct mass flow rates computed
from bi-directional probe data. The intermediate scale
of the flow field was sufficient to test the performance
of a current PIV system and to identify the requirements
for conducting successful PIV measurements in a
full-scale fire experiment.