Benchmark Experiments for Turbulent Mixing in the Scaled-Down Upper Plenum of High-Temperature Gas-Cooled Reactors Under Accident Scenario

Abstract

The time-averaged particle image velocimetry technique has been applied to measure flow mixing in the Michigan Multi-jet Gas-mixture Dome (MiGaDome) facility, a 1/12th, scaled-down model of the high-temperature gas-cooled reactor upper plenum. Measurements were first conducted with one jet injection into the upper plenum for various Reynolds numbers (Re = 1022, 2038, 4097, and 6021). The experimental region of interest includes a plane within the dome located above one of the jet inlets of interest. First- and second-order statistics are presented and discussed to analyze the local mixing process and turbulent characteristics under the effects of jet spreading and jet impingement. Results have shown that the normalized statistics of the jet reach asymptotic behavior as the inlet Reynolds number is increased. By investigating the two-dimensional budgets for the momentum equation on the measurement plane, it was concluded that the contribution of turbulent diffusion is minor near the enclosure surface where strong convection is present due to impingement. An additional measurement on a triple-jet injection case has shown that jet spreading is suppressed by a recirculation zone, which causes a redistribution of turbulent fluctuations. The detailed local fluctuation patterns/coherent structures have been examined through a proper orthogonal decomposition analysis.

Keywords:

• Particle image velocimetry
• turbulent mixing
• HTGR upper plenum
• proper orthogonal decomposition
• budgets

Disclosure Statement

No potential conflict of interest was reported by the authors.

Nomenclature

$\mathit{D}$	=	= inlet diameter (m)
$\bar{g}$	=	= gravitational acceleration (m/s2)
$\mathit{H}$	=	= jet inlet to the surface distance (m)
$\mathit{k}$	=	= POD mode number
$\bar{P}$	=	= pressure (Pa)
Re	=	= Reynolds number
$\mathit{r}$	=	= inlet pipe radius (m)
$\mathit{t}$	=	= time (s)
$\bar{U}$	=	= crosswise velocity (m/s)
$\mathit{u}{ }^{\mathrm{\prime }}$	=	= crosswise velocity fluctuation (m/s)
$\overline{\mathit{u}{\mathit{ }}^{\mathrm{\prime }}\mathit{u}{ }^{\mathrm{\prime }}}$	=	= crosswise Reynolds normal stress (m2/s2)
$\overline{\mathit{u}{\mathit{ }}^{\mathrm{\prime }}\mathit{v}{ }^{\mathrm{\prime }}}$	=	= Reynolds shear stress normal to XY plane (m2/s2)
$\overline{\mathit{u}{\mathit{ }}^{\mathrm{\prime }}\mathit{w}{ }^{\mathrm{\prime }}}$	=	= Reynolds shear stress normal to XZ plane (m2/s2)
$\bar{V}$	=	= streamwise velocity (m/s)
${\bar{V}}_{\mathit{c}}$	=	= inlet pipe centerline velocity (m/s)
$V_{\mathit{in}}$	=	= inlet average velocity (m/s)
${\bar{V}}_{\mathit{mag}}$	=	= average velocity magnitude (m/s)
$\mathit{v}{ }^{\mathrm{\prime }}$	=	= streamwise velocity fluctuation (m/s)
$\overline{\mathit{v}{\mathit{ }}^{\mathrm{\prime }}\mathit{v}{ }^{\mathrm{\prime }}}$	=	= streamwise Reynolds normal stress (m2/s2)
$\overline{\mathit{v}{\mathit{ }}^{\mathrm{\prime }}\mathit{w}{ }^{\mathrm{\prime }}}$	=	= Reynolds shear stress normal to YZ plane (m2/s2)
$\bar{W}$	=	= out-of-plane velocity (m/s)
$\mathit{w}{ }^{\mathrm{\prime }}$	=	= out-of-plane velocity fluctuation (m/s)
$x_{1/2}$	=	= jet half-width (m)
$\mathit{x},\mathit{y},\mathit{z}$	=	= coordinates (m)

Greek

$a_k$	=	= POD mode time coefficient
$\mathit{\sigma }$	=	= uncertainty sources
${\mathrm{\Phi }}_k$	=	= POD k’th mode
$\mathit{\nu }$	=	= viscosity (m2/s)
$\mathit{\rho }$	=	= density (kg/m3)
${\omega }_z$	=	= vorticity on the z-plane (1/s)

Additional information

Funding

This work was co-funded by the Nuclear Energy University Program (DE-NE0008782) and the IRP entitled “Center of Excellence for Thermal-Fluids Applications in Nuclear Energy: Establishing the Knowledgebase for Thermal-Hydraulic Multiscale Simulation to Accelerate the Deployment of Advanced Reactors—IRP-NEAMS-1.1: Thermal-Fluids Applications in Nuclear Energy” from the U.S. Department of Energy (DOE). The authors are thankful for the financial support from the DOE office and appreciate the insightful suggestions from all colleagues under these two projects.