Turbulence modification and heat transfer enhancement by inertial particles in turbulent channel flow

Abstract

We present results of direct numerical simulation of turbulence modification and heat transfer in turbulent particle-laden channel flow and show an enhancement of the heat transfer and a small increase in the friction velocity when heavy inertial particles with high specific heat capacity are added to the flow. The simulations employ a coupled Eulerian-Lagrangian computational model in which the momentum and energy transfer between the discrete particles and the continuous fluid phase are fully taken into account. The effect of turbophoresis, resulting in an increased particle concentration near a solid wall due to the inhomogeneity of the wall-normal velocity fluctuations, is shown to be responsible for an increase in heat transfer. As a result of turbophoresis, the effective macroscopic transport properties in the region near the walls differ from those in the bulk of the flow. To support the turbophoresis interpretation of the enhanced heat transfer, results of simulations employing no particle-fluid coupling and simulations with two-way coupling at considerably lower specific heat, or considerably lower particle concentration are also included. The combination of these simulations allows distinguishing contributions to the Nusselt number due to mean flow, turbulent fluctuations and explicit particle effects. We observe an increase in Nusselt number by more than a factor of two for heavy inertial particles, which is the net result of a decrease in heat transfer by turbulent velocity fluctuations and a much larger increase in heat transfer stemming from the mean temperature difference between the fluid and the particles close to the walls.

Lagrangian statistics of turbulent channel flow at Reτ = 950 calculated with direct numerical simulation and Langevin models

“…8, it can be seen that the wall-normal diffusion coefficient obtained from DNS agrees reasonably well with the result obtained from the statistical model according to Eq. (16), in which the effect of finite viscosity is taken into account. Results from the DNS divided by the theoretical values according to Eq.…”

“…Also at lower frictional Reynolds numbers the numerical method has been validated by comparison with results from literature. 16 In order to calculate Lagrangian velocity correlation functions passive tracers are added to the flow. They obey the equation…”

Turbulence attenuation in particle-laden flow in smooth and rough channels

“…If we include PP-DNS of horizontal or non-gravitational particle-laden plane channel flows in our discussion, one-way coupled simulations of such flows were (for example) performed at Re τ = 150 (Pedinotti, Mariotti & Banerjee 1992;Marchioli & Soldati 2002), Re τ = 300 (Lavezzo et al 2010) and Re τ = 950 (Geurts & Kuerten 2012;Kuerten & Brouwers 2013), two-way coupled simulations up to Re τ = 395 (Kuerten, van der Geld & Geurts 2011;Zhao, Andersson & Gillissen 2013) and two-way coupled simulations with inter-particle collisions at Re τ = 125 (Nasr, Ahmadi & McLaughlin 2009).…”

Rotating turbulent Rayleigh–Bénard convection subject to harmonically forced flow reversals

“…At constant rotation rate, a maximum increase of about 15% compared to the Nusselt number in the non-rotating case was reported in case water was used [5] while a maximal value of up to 40% was found in case the Prandtl number of the working liquid was varied [6]. This is small compared to heat transfer intensification associated with phase transitions [7]. In the latter, the transport of heat can be strengthened via evaporation and condensation, bringing latent heat contributions into play.…”