turbulent mixing; temperature fluctuations; tee junctions; thermal fatigue; RANS; temperature fluctuation transport model; wire-mesh sensors; parallel; Reynolds Averaged Navier Stokes;
(2014), Large Eddy Simulation of Turbulent Penetration in a T-junction, in International Congress on Advances in Nuclear Power Plants (ICAPP 2014)
, Charlotte, U.S.A..
(2014), The Influence of Density Stratification and T-junction Geometry on Turbulent Penetration, in International Topical Meeting on Nuclear Thermal Hydraulics, Operation and Safety (NUTHOS-10)
, Okinawa, Japan.
(2014), Turbulent Penetration in T-junction Branch Lines with Leakage Flow, in Nuclear Engineering and Design
, 276, 43-53.
(2012), Steady State RANS Simulations of Temperature Fluctuation in a Single Phase Turbulent Mixing, in International Congress on Advances in Nuclear Power Plants 2012, ICAPP 2012
, Chicago, USA.
(2012), Turbulent Penetration as a Thermal Fatigue Problem in low Side Flow T-Junctions, in Nuclear Thermal Hydraulics and Safety 8 (NTHAS8)
, Beppu, Japan.
, Wire Mesh Sensor for High Temperature High Pressure Applications, in 16th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-16)
, Chicago, USA.
Turbulent mixing of streams with different temperature may cause significant temperature fluctuations in the walls of pipes and other components of power plants or other industrial installations. These fluctuations may cause thermal fatigue in the wall material and pose a risk to the safety and reliability of the plant. The proposed project is focused on the prediction of temperature fluctuations in a T-junction by techniques of experimental simulation and a contribution to the theoretical prediction for arbitrary geometries by means of an extension and validation of Reynolds Averaged Navier-Stokes (RANS) modeling. For the experimental part, a co-operation with the Laboratory of Nuclear Power (IKE) of the University of Stuttgart will be established. IKE has started to develop and construct a T-junction experiment that will provide measuring data on the velocity and temperature fields inside the flow domain at operating parameters of an original nuclear power plant for the first time. High parameters pose a number of limitations to the applicability of measuring methods. For this reason, temperature information will be obtained only at a limited number of locations by the use of thermocouples. It is therefore proposed to construct a second test facility, the test geometry of which is an identical copy of the IKE T-junction to perform mixing experiments at room temperature. Mesh sensor techniques based on detection of electrical conductivity will be used instead of thermocouples. These sensors provide two-dimensional distributions of the transport scalar at hundreds of individual measuring positions with a time resolution of up to 10 kHz and are from this point o view extremely superior to thermocouples. The temperature as transport scalar is simulated by an addition of a tracer salt that increases the electrical conductivity of the fluid. In this way, mixing patterns become visible to mesh sensors. As an alternative, it is planned to detect temperature fluctuations directly via the temperature dependency of the electrical conductivity of water, which is less accurate but opens to door to non-adiabatic tests at the cold, non-pressurized test rig. Beside flow instrumentation, the IKE T-junction is equipped with strain gauges, too. Tests will be performed until failure of the tested component, which allows mechanical testing of the fragments. It is a considerable added value of the proposed exchange of experimental results that also the data of the structural behavior will be made available to the Swiss partner. The theoretical part of the proposed PhD project aims at predicting temperature fluctuations by means of steady-state RANS simulations. This is interesting from a practical point of view: LES, which has been found to be the ideal tool to predict the temperature fluctuations, becomes too expensive when more complex and larger geometries typical for industrial plants have to be analyzed. In previous work, it has been demonstrated that solving Reynolds stress equations coupled with a transport equation for the temperature fluctuations reduce computational costs compared to LES by orders of magnitude. Still, with this technique it is possible to obtain distributions of the RMS of the fluid temperature. It is the task of the PhD student to perform numerical simulations aiming at a validation of this model and to explore possibilities for assessing the resulting temperature fluctuations in the wetted wall, as well as their characteristic frequency range.