Velocity, Temperature, and Turbulence Measurements in Air for Pipe Flow With Combined Free and Forced Convection

Abstract

Experimental results are presented for velocity and temperature profiles and for the turbulence quantities vz′ t′ and vzt, for up-flow of air in a vertical pipe with constant heat flux at Reynolds numbers of 5000 to 14,000. The measurements show that, with increasing heat flux, superimposed free convection effects cause marked distortion of the flow structure at low Reynolds numbers, with the velocity maximum moving from the tube center to a position near the wall. The axial turbulence intensity, vz′, is depressed by increasing heat flux while the temperature intensity, t′, first decreases and then rises, with a shift in the position of the peak intensity away from the wall. On the basis of an analysis developed for heated turbulent flow, the turbulent shear stress and heat flux distributions are calculated from the experimental results. As the flow field becomes appreciably distorted on heating, it is found that the turbulent shear stress becomes very small, while the heat flux distribution suggests an increase in the width of the viscous sublayer.

Assessment of a common nonlinear eddy-viscosity turbulence model in capturing laminarization in mixed convection flows

“…In their DNS work, You et al [18] explained that while their results did not agree well with experimental data obtained by imposing the total pressure drop (e.g., Parlatan et al [27]), they observed closer agreement with those obtained by measurement of velocity gradient instead (e.g., Carr et al [26]). In addition, discrepancies are likely to arise from different methods of measuring c f .…”

“…In the case of the LS model this is, at least in part, related to its underprediction of c f0 by about 8% (Table 5). In turn, this results in an earlier onset of friction coefficient enhancement compared with the experimental results of Carr et al [26] and DNS data. In comparison with the LS model, the results of the Suga model indicate a steeper enhancement gradient.…”

“…The Nusselt number in mixed convection, Nu, is normalized by the corresponding forced convection value evaluated at the same Reynolds and Prandtl numbers, and Nu/Nu 0 is plotted against the buoyancy parameter, Bo. The DNS data of You et al [18], and the experimental results of Steiner [25], Carr et al [26], and Parlatan et al [27] are also included. The most remarkable observation from Figure 1 is the dramatic reduction in heat transfer levels occurring in the interval 0.15 < Bo < 0.25.…”

Refined Eddy Viscosity Schemes and Large Eddy Simulations for Ascending Mixed Convection Flows

“…Four simulations are reported by You et al and these are detailed in Table 7 Also represented in Fig. 4 are the data of Steiner [1971], Carr et al [1973] and Parlatan et al [1996]. While these data were obtained for values of Re, Pr, and Gr different from those of You et al, all are cast in terms of Bo.…”

“…Experimental studies of ascending mixed convection air flows include the works of Steiner [1971], Carr et al [1973], Polyakov and Shindin [1988], Vilemas et al [1992] and Shehata and McEligot [1998]. Results for water flows are reported by Parlatan et al [1996].…”