Effect of turbulent integral length scale on heat transfer around a circular cylinder placed cross to an air flow

Development of flat-plate thermal and velocity boundary layers under highly turbulent and instable air flows: Reynolds numbers ranging from 8400 to 127000

“…Each level of Tu ∞ had also to remain nearly constant in the flow direction all along the flat plate. To reach this goal, perforated plates with different values of Φ g and σ g were chosen using previous studies [2,3,18]. Turbulence intensities of about 6, 12 and 40% were obtained along the test chamber using plates whose characteristics and location are given in Table 1.…”

“…The free stream turbulence was a decaying turbulence. The ratio of the longitudinal component to the transverse component of the velocity fluctuation has been measured in previous studies downstream of promoters (1), (2) and (4) in several points along the experimental chamber using in addition to the 90 • -wire probe a single rotated 45 • -wire probe [2,18]. This ratio ranged from 0.8 to 1.2 depending on the promoter which is require (but not sufficient) for a flow turbulence to be isotropic.…”

“…The length of the flat plate used for the boundary layer measurements was located in an area corresponding to the plateaus of these decreasing curves. Details on the flow downstream promoters (1), (2) and (4) and relations which make it possible to connect the different turbulent scales are given in references [2,18]. Only the extreme values of these plateaus are given in Table 1.…”

“…Only the extreme values of these plateaus are given in Table 1. The procedure used to determine the turbulence integral length scales from turbulent spectra downstream of promoter (1), (2) and (4) are detailed in reference [18]. The use of two different turbulence promoters (2) and (4) (located either upstream or downstream of the contraction area) to obtain a free stream turbulence intensity of 12% made it possible to reach different turbulent scales in the test chamber under a similar value of Tu ∞ .…”

Application of particle image velocimetry measurement techniques to study turbulence characteristics of oscillatory flows around parallel-plate structures in thermoacoustic devices

“…The heat transfer coefficient, Nu, when the turbulence intensity is 40%, has a value of about two times its value when the turbulence intensity is 1.5%, which suggests that it is the small-scale turbulence (as opposed to large coherent structures) that is a major contributor to the heat transfer mechanisms. References [52,53] also investigated the effects that the integral length scale, which characterises the dimension of eddies in the flow, may have on the heat transfer.…”