Experimental study on flow characteristics of a large-scale open jet wind tunnel for outdoor pool fire research

An open jet wind tunnel with an exit area of 23 x 9 m(2) has been built to study the behaviors of large-scale pool fires under controlled wind conditions. A series of measurements on the mean and fluctuating wind velocities, using arrays of hot-wire probes and ultrasonic anemometers, were extensively performed in the transverse planes at the leading and trailing edges of the pool (28 m and 48 m to the exit). The entire pool was located in the potential core of the central jet flow region, and the longitudinal velocity (U) and turbulence intensity (I-u) exhibited acceptable uniform distributions within the two vertical planes. The mean turbulence intensities in the two planes were close to those in the flat open grassland and sea (7%-10%). The longitudinal velocity spectra were in good agreement with the Von Karman spectrum at all levels, and the onset frequency for isotropy was about 1.5-3.0 Hz. In the central flow region, the turbulence dissipation rates (epsilon) were fitted well by epsilon = 0.067U(2.69)I(u)(1.90), and the best-fit line for the turbulent diffusivity (nu(t)) was nu(t) = 0.21(0.95)I(u)(0.98). The detailed mean flow and turbulence characteristics provided the necessary information for the pool fire tests and numerical model verification.