Abstract: This paper reports an experimental investigation of the energy spectrum of turbulent velocity fields at low Reynolds numbers in grid turbulence. Hot wire measurements are carried out in grid turbulence with subjected to a 1.36:1 contraction of the wind tunnel. Three different grids are used: (i) large square perforated grid (mesh size 43.75mm), (ii) small square perforated grid (mesh size 14. and (iii) woven mesh grid (mesh size 5mm). The results indicate that the energy spectrum at small Reynolds numbers does not follow Kolmogorov’s universal scaling. It is further found that the critical Reynolds number, below which the scaling breaks down, is around 25.
Abstract: Linear stochastic estimation and quadratic stochastic
estimation techniques were applied to estimate the entire velocity
flow-field of an open cavity with a length to depth ratio of 2. The
estimations were done through the use of instantaneous velocity
magnitude as estimators. These measurements were obtained by
Particle Image Velocimetry. The predicted flow was compared
against the original flow-field in terms of the Reynolds stresses and
turbulent kinetic energy. Quadratic stochastic estimation proved to be
more superior than linear stochastic estimation in resolving the shear
layer flow. When the velocity fluctuations were scaled up in the
quadratic estimate, both the time-averaged quantities and the
instantaneous cavity flow can be predicted to a rather accurate extent.