Optical diagnostics of convective structures induced by non-stationary boundary conditions in a vertical water layer

2018 ◽  
Vol 10 (4) ◽  
pp. 134-144 ◽  
Author(s):  
Yu.N. Dubnishchev ◽  
V.A. Arbuzov ◽  
E.V. Arbuzov ◽  
V.S. Berdnikov ◽  
S.A. Kislytsin ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Optical Diagnostics ◽  
Water Layer ◽  
Stationary Boundary ◽  
Convective Structures

scholarly journals Study of convective structures and phase transition induced in a water layer by non-stationary boundary conditions

2019 ◽  
Vol 1421 ◽  
pp. 012047
Author(s):  
Yu N Dubnishchev ◽  
V A Arbuzov ◽  
E V Arbuzov ◽  
V S Berdnikov ◽  
O S Zolotukhina ◽  
...  
Keyword(s):  
Phase Transition ◽  
Boundary Conditions ◽  
Water Layer ◽  
Stationary Boundary ◽  
Convective Structures

scholarly journals Investigation of convective structures and phase transition induced by non-stationary boundary conditions in a horizontal layer of water

2019 ◽  
Author(s):  
Виталий Арбузов ◽  
Vitaliy Arbuzov ◽  
Эдуард Арбузов ◽  
Eduard Arbuzov ◽  
Владимир Бердников ◽  
...  
Keyword(s):  
Phase Transition ◽  
Boundary Conditions ◽  
Water Layer ◽  
Horizontal Layer ◽  
Temperature Fields ◽  
Special Importance ◽  
Stationary Boundary ◽  
Convective Structures ◽  
Numerical Simulation Methods ◽  
Lower Heat

The evolution of convective structures and the phase transition induced by non-stationary boundary conditions in a horizontal water layer bounded by flat heat-exchange surfaces were studied by shear interferometry and numerical simulation methods. Numerical modeling of the temperature field as a field of isotherms in the mode of monotonous cooling of horizontal walls was performed. The problem of fragmentary reconstruction of hilbertograms and shear interferograms images from a numerical model of the isotherm field was solved. The hydrodynamics of convective currents, the coevolution of temperature fields, interference and Hilbert structures have been modeled and studied taking into account the inversion of water density in the vicinity of the isotherm (+4°C), under conditions of phase transition and growth of the ice layer on the lower heat transfer plane. The simulation was performed using a proprietary software package. The relevance of this kind of research is due to the special importance of convection in geodynamics, physics of the atmosphere and the ocean, in hydrodynamic and thermophysical processes associated with the formation and growth of crystals.

A New Method to Simulate Rotor-Stator Interactions in a Centrifugal Pump Stage

2006 ◽  
Author(s):  
Jianjun Feng ◽  
Friedrich-Karl Benra ◽  
Hans Josef Dohmen
Keyword(s):  
Boundary Conditions ◽  
Centrifugal Pump ◽  
Mass Flow ◽  
New Method ◽  
Water Tank ◽  
Mean Flow ◽  
Vaned Diffuser ◽  
Stationary Boundary ◽  
Flow Fluctuation ◽  
Return Channel

A new method is put forward to model rotor-stator interactions in the first stage of a multistage centrifugal pump consisting of an impeller, a vaned diffuser and a vaned return channel. A directional loss model is utilized to model the function of a water tank behind the return channel. A periodic boundary condition between the inlet and the outlet is applied to model a closed loop. Thus no flow specification either in the inlet or outlet is required, neither is the turbulence level. Consequently it can avoid specifying unphysical stationary boundary conditions at the inlet and the outlet for transient simulations. Transient numerical results are compared with those by the conventional simulation with stationary boundary conditions (constant total pressure at the inlet and fixed mass flow at the outlet) in detail. The new model can predict the mass flow fluctuation in the pump, which reaches 0.5% of mean flow rate during one period. The mass flow fluctuation does not have a significant influence on the velocity field; however it does have some important effects on the pressure and turbulent kinetic energy fields.

scholarly journals Mesoscale nesting interface of the PALM model system 6.0

2020 ◽  
Author(s):  
Eckhard Kadasch ◽  
Matthias Sühring ◽  
Tobias Gronemeier ◽  
Siegfried Raasch
Keyword(s):  
Boundary Layer ◽  
Boundary Conditions ◽  
Atmospheric Boundary Layer ◽  
Mesoscale Model ◽  
Model System ◽  
Convective Boundary ◽  
Convective Structures ◽  
Eddy Simulation ◽  
Synoptic Conditions ◽  
Turbulence Generation

Abstract. In this paper, we present a newly developed mesoscale nesting interface for the PALM model system 6.0, which enables PALM to simulate the atmospheric boundary layer under spatially heterogeneous and non-stationary synoptic conditions. The implemented nesting interface, which is currently tailored to the mesoscale model COSMO, consists of two major parts: (i) the preprocessor INIFOR, which provides initial and time-dependent boundary conditions from mesoscale model output and (ii) PALM's internal routines for reading the provided forcing data and superimposing synthetic turbulence to accelerate the transition to a fully developed turbulent atmospheric boundary layer. We describe in detail the conversion between the sets of prognostic variables, transformations between model coordinate systems, as well as data interpolation onto PALM's grid, which are carried out by INIFOR. Furthermore, we describe PALM's internal usage of the provided forcing data, which besides the temporal interpolation of boundary conditions and removal of any residual divergence includes the generation of stability-dependent synthetic turbulence at the inflow boundaries in order to accelerate the transition from the turbulence-free mesoscale solution to a resolved turbulent flow. We demonstrate and evaluate the nesting interface by means of a semi-idealized benchmark case. We carried out a large-eddy simulation (LES) of an evolving convective boundary layer on a clear-sky spring day. Besides verifying that changes in the inflow conditions enter into and successively propagate through the PALM domain, we focus our analysis on the effectiveness of the synthetic turbulence generation. By analysing various turbulence statistics, we show that the inflow in the present case is fully adjusted after having propagated for about 1.5 eddy turn-over times downstream, which corresponds well to other state-of-the-art methods for turbulence generation. Furthermore, we observe that numerical artefacts in the form of under-resolved convective structures in the mesoscale model enter the PALM domain, biasing the location of the turbulent up- and downdrafts in the LES. With these findings presented, we aim to verify the mesoscale nesting approach implemented in PALM, point out specific shortcomings, and build a baseline for future improvements and developments.

scholarly journals Mesoscale nesting interface of the PALM model system 6.0

2021 ◽  
Vol 14 (9) ◽  
pp. 5435-5465
Author(s):  
Eckhard Kadasch ◽  
Matthias Sühring ◽  
Tobias Gronemeier ◽  
Siegfried Raasch
Keyword(s):  
Boundary Layer ◽  
Boundary Conditions ◽  
Atmospheric Boundary Layer ◽  
Mesoscale Model ◽  
Model System ◽  
Convective Boundary ◽  
Convective Structures ◽  
Eddy Simulation ◽  
Synoptic Conditions ◽  
Turbulence Generation

Abstract. In this paper, we present a newly developed mesoscale nesting interface for the PALM model system 6.0, which enables PALM to simulate the atmospheric boundary layer under spatially heterogeneous and non-stationary synoptic conditions. The implemented nesting interface, which is currently tailored to the mesoscale model COSMO, consists of two major parts: (i) the preprocessor INIFOR (initialization and forcing), which provides initial and time-dependent boundary conditions from mesoscale model output, and (ii) PALM's internal routines for reading the provided forcing data and superimposing synthetic turbulence to accelerate the transition to a fully developed turbulent atmospheric boundary layer. We describe in detail the conversion between the sets of prognostic variables, transformations between model coordinate systems, as well as data interpolation onto PALM's grid, which are carried out by INIFOR. Furthermore, we describe PALM's internal usage of the provided forcing data, which, besides the temporal interpolation of boundary conditions and removal of any residual divergence, includes the generation of stability-dependent synthetic turbulence at the inflow boundaries in order to accelerate the transition from the turbulence-free mesoscale solution to a resolved turbulent flow. We demonstrate and evaluate the nesting interface by means of a semi-idealized benchmark case. We carried out a large-eddy simulation (LES) of an evolving convective boundary layer on a clear-sky spring day. Besides verifying that changes in the inflow conditions enter into and successively propagate through the PALM domain, we focus our analysis on the effectiveness of the synthetic turbulence generation. By analysing various turbulence statistics, we show that the inflow in the present case is fully adjusted after having propagated for about two to three eddy-turnover times downstream, which corresponds well to other state-of-the-art methods for turbulence generation. Furthermore, we observe that numerical artefacts in the form of grid-scale convective structures in the mesoscale model enter the PALM domain, biasing the location of the turbulent up- and downdrafts in the LES. With these findings presented, we aim to verify the mesoscale nesting approach implemented in PALM, point out specific shortcomings, and build a baseline for future improvements and developments.

Evaluation of the Thermal Resistance of Structure with Reflective Insulation: Measurement under Non-Stationary Boundary Conditions

2014 ◽  
Vol 1041 ◽  
pp. 150-153
Author(s):  
Jiří Kalánek ◽  
Libor Šteffek ◽  
Milan Ostrý
Keyword(s):  
Heat Transfer ◽  
Boundary Conditions ◽  
Thermal Radiation ◽  
Thermal Resistance ◽  
Thermal Insulation ◽  
Experimental Measurements ◽  
International Standard ◽  
Stationary Boundary

Some manufacturers of reflective insulation products claim that their relatively thin products have the same thermal insulation properties as common insulation with much times higher thickness. This paper deals with experimental measurements of the thermal insulation properties of real structures with reflective insulation. Several experimental sequences were conducted to determine the thermal resistance of the structure. The evaluation was conducted according to the procedures specified in the international standard (ISO 9869 - 1994). Effect of products (based on the reflection of thermal radiation) on the thermal insulation properties of the structure will be determined by evaluation. This effect will be compared with the effects of common insulation (with the intention of reduce of the heat transfer by the conduction).

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