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AbstractThis technical note deals with simulation-based design optimization for the ex-core Transformational Challenge Reactor (TCR). Three-dimensional geometry was created for the TCR ex-core. Computational fluid dynamics (CFD) simulations were performed to optimize forced circulation airflow. The CFD model includes thermofluidic phenomena such as convective, conductive, and radiative heat transfer. The simulation results are presented for three different inlet coolant mass flow rates (2, 4, and 8 kg/s). The observed optimized flow rate for the base configuration was 5 kg/s. The calculated peak temperatures were within the safety limits for all components including the bio-shield (433 K) and the shroud mechanism (473 K).

AbstractTo enable the design of a light water small modular reactor, the boiling flow inside a helical coil steam generator has been simulated with the two-fluid model in Nek-2P. Nek-2P is the multiphase branch of the spectral element code Nek5000. Details of the implementation of the two-fluid model and the included closure models are discussed. The presented closure models include interactions for momentum, heat, and mass transfer between phases. Models for the drag, lift, and turbulent dispersion forces are included. The complete model is fully consistent in the limits of both phasic volume fractions approaching zero and is able to simulate flows of dispersed vapor, continuous liquid, dispersed liquid, continuous vapor, or any combination thereof. The closure models and their implementation in Nek-2P have been validated by comparing to experimental data for a boiling flow, demonstrating excellent agreement. Results from the simulation of the helical coil indicate strong phasic separation driven by the effects of buoyancy and inertia. Significant differences were observed in the results compared to simulations performed using Star-CCM+, although these differences were somewhat expected.

Computational fluid dynamics (CFD) simulations in 3D are performed to analyse the aerodynamic drag performance of a truck for two different on-highway road tunnel dimensions. The objective of this work is to investigate the aerodynamic drag performance of single- and multiple vehicle platooning configurations in single- and multi-lane one-way road traffic condition. Significant aerodynamic drag benefit is observed in no-traffic vehicle with an increase in gap between vehicle and road tunnel. In the vehicle platooning, the predicted aerodynamic drag benefit is up to 23% at lower vehicle separation. The aerodynamic drag benefit gradually drops in one-lane traffic and negative performance is observed from 60ft separation distance onwards. In two-lane traffic, where one vehicle is behind the other without a lateral separation, the predicted aerodynamic drag benefit is up to 60 and 44% at vehicle separation distance of 30 and 150ft, respectively. The aerodynamic drag changes are negligible with an increase in vehicle separation distance where two vehicles are separated laterally with 1.2 m distance. In all configurations, the leading vehicle aerodynamic drag changes are negligible irrespective of the vehicle separation distance.

External aerodynamics and underhood thermal analyses of two heavy-duty vehicles, (1) cab-over engine (European style flat-front) and (2) conventional truck (North American class-8-style front engine), are being studied to assess their aerodynamic and underhood cooling performances. Both vehicles have similar geometrical dimensions, i.e. width, height and length. Three-dimensional computational fluid dynamics modelling and simulations are performed using StarCCM+® commercial software. Aerodynamic drag analysis is carried out separately for each configuration. Significant fuel savings are observed in a conventional truck when compared to cab-over engine configurations at all yaw angles. The major reduction in fuel consumption is observed mainly from the cabin designs alone (up to 7.5%). Apart from the aerodynamic drag analysis, underhood thermal analysis is also performed to compare both heavy-duty vehicle configurations. Based on the coolant temperatures, 12 and 10% thermal efficiency improvements are observed in conventional trucks when compared to cab-over engine for charge air cooler and radiator, respectively.

This paper discusses the modeling and simulations of deteriorated turbulent heat transfer (DTHT) for a wall-heated fluid flows, which can be observed in gas-cooled nuclear power reactors during pressurized conduction cooldown (PCC) event due to loss of force circulation flow. The DTHT regime is defined as the deterioration of normal turbulent heat transport due to increase of acceleration and buoyancy forces. The computational fluid dynamics (CFD) tools such as Nek5000 and STAR-CCM+ can help to analyze the DTHT phenomena in reactors for efficient thermal-fluid designs. Three-dimensional (3D) CFD nonisothermal modeling and simulations were performed in a wall-heated circular tube. The simulation results were validated with two different CFD tools, Nek5000 and STAR-CCM+, and validated with an experimental data. The predicted bulk temperatures were identical in both CFD tools, as expected. Good agreement between simulated results and measured data were obtained for wall temperatures along the tube axis using Nek5000. In STAR-CCM+, the under-predicted wall temperatures were mainly due to higher turbulence in the wall region. In STAR-CCM+, the predicted DTHT was over 48% at outlet when compared to inlet heat transfer values.