Victor Petrov

Bottlenose dolphins modify behavior to reduce metabolic effect of tag attachment.

Attaching bio-telemetry or -logging devices (‘tags’) to marine animals for research and monitoring adds drag to streamlined bodies, thus affecting posture, swimming gaits and energy balance. These costs have never been measured in free-swimming cetaceans. To examine the effect of drag from a tag on metabolic rate, cost of transport and swimming behavior, four captive male dolphins (Tursiops truncatus) were trained to swim a set course, either non-tagged (n=7) or fitted with a tag (DTAG2; n=12), and surface exclusively in a flow-through respirometer in which oxygen consumption () and carbon dioxide production (; ml kg−1 min−1) rates were measured and respiratory exchange ratio (/) was calculated. Tags did not significantly affect individual mass-specific oxygen consumption, physical activity ratios (exercise /resting ), total or net cost of transport (COT; J m−1 kg−1) or locomotor costs during swimming or two-minute recovery phases. However, individuals swam significantly slower when tagged (by ~11%; mean ± s.d., 3.31±0.35 m s−1) than when non-tagged (3.73±0.41 m s−1). A combined theoretical and computational fluid dynamics model estimating drag forces and power exertion during swimming suggests that drag loading and energy consumption are reduced at lower swimming speeds. Bottlenose dolphins in the specific swimming task in this experiment slowed to the point where the tag yielded no increases in drag or power, while showing no difference in metabolic parameters when instrumented with a DTAG2. These results, and our observations, suggest that animals modify their behavior to maintain metabolic output and energy expenditure when faced with tag-induced drag.

Parameter Sensitivity Study of Boiling and Two-Phase Flow Models in CFD

This work presents a sensitivity study of boiling and two phase flow models for thermal hydraulics simulations in nuclear reactors. This study quantifies sources of uncertainty and error in these simulations by computing global sensitivities of figures of merit, or output, to model parameters, inputs, and mesh resolution. Results are obtained for the DEBORA benchmark problem of boiling in a channel driven by a heated wall section. Scalar outputs of interest consist of axial pressure drop, average wall temperature in the heated section, average void fraction at the end of the heated section, and the centroid of the radial distribution of the void fraction at the end of the heated test section. Sensitivities to both individual heat fluxes and to the parameters in the models for these heat fluxes are computed.

Analysis of Void Fraction Distribution and Departure from Nucleate Boiling in Single Subchannel and Bundle Geometries Using Subchannel, System, and Computational Fluid Dynamics Codes

In order to assess the accuracy and validity of subchannel, system, and computational fluid dynamics codes, the Paul Scherrer Institut has participated in the OECD/NRC PSBT benchmark with the thermal-hydraulic system code TRACE5.0 developed by US NRC, the subchannel code FLICA4 developed by CEA, and the computational fluid dynamic code STAR-CD developed by CD-adapco. The PSBT benchmark consists of a series of void distribution exercises and departure from nucleate boiling exercises. The results reveal that the prediction by the subchannel code FLICA4 agrees with the experimental data reasonably well in both steady-state and transient conditions. The analyses of single-subchannel experiments by means of the computational fluid dynamic code STAR-CD with the CD-adapco boiling model indicate that the prediction of the void fraction has no significant discrepancy from the experiments. The analyses with TRACE point out the necessity to perform additional assessment of the subcooled boiling model and bulk condensation model of TRACE.

High-Resolution Velocity Field Measurements of Turbulent Round Free Jets in Uniform Environments

Abstract Turbulent round free jets are one of the most common jet types, which have been intensively studied in the research community for over 90 years. Due to its characteristics of momentum transport in free shear layers, this type of jet is widely used in several industrial applications varying from nuclear reactor safety analysis to aerospace jet engine designs. Focusing on close-to-jet (near-field) and self-similar regions, the entrainment and momentum transport can be properly described by the Reynolds numbers of the flow fields. To establish a nonconfined free jet, an experimental facility was built with a jet nozzle diameter of 12.7 mm, located at the bottom of a cubic tank with a 1-m side length. The jet flow is realized by a servo-motor-driven piston to avoid possible fluctuations introduced by other motor options. Nominal jet Reynolds numbers range from 5000 up to 22 500. High-speed and time-resolved particle imaging velocimetry techniques are used to measure the velocity fields in the vertical midplane of the jet for both investigated flow fields. The adopted setup has a spatial resolution of 209 × 209 µm2 for near-field regions and 684 × 684 µm2 for self-similar regions and thus covers the Taylor microscale for all cases presented in this paper. Experimental results are presented in terms of turbulent statistics and the frequency spectrum of the velocities. The sources of uncertainties associated with the measured velocity field are quantified. The results are in good agreement with previously published data. The obtained energy spectra confirm Kolmogorov’s theory in the inertial subrange. Coherent structures, obtained with two-point spatial correlations of variances of velocities, show growth in penetration depth with increased downstream distance, which is consistent with the analysis of temporal correlation fields.

Numerical Study of Integral Inherently Safe Light Water Reactor in Case of Inadvertent DHR Operation Based on the Multiscale Method

Abstract In detailed previous work by the authors, an innovative decay heat removal (DHR) system has been proposed and designed for the Integral Inherently Safe Light Water Reactor (I2S-LWR). The current paper studies the inadvertent actuation of one DHR system train during I2S-LWR normal operation due to a false signal or operator action. The RELAP5 code is used to perform a one-dimensional study, and important thermal-hydraulic characteristics, including primary loop coolant flow rate, pressure, temperature, DHR primary-side flow rate, and coolant temperature, are achieved during this transient. Then, a detailed computational fluid dynamics simulation utilizing STARCCM+ is carried out to investigate the coolant mixing characteristics in the downcomer and lower plenum and obtain the local thermal-hydraulic conditions at the reactor core inlet. It is found that as a consequence of inadvertent DHR actuation, the maximum overcooling at the reactor core inlet is about 3 K, which would not result in significant reactivity insertion. Furthermore, a more severe transient of inadvertent DHR operation with intermediate loop break is studied, and the results show that this would not lead to more significant overcooling to the I2S-LWR core compared with inadvertent DHR operation without intermediate loop break. This work is an indispensable supplement for DHR system comprehensive assessment in the I2S-LWR project.

An Experimental Study of Local Self-Similarity in the Mixing Transition of a Turbulent Free Jet

Abstract Turbulent free jets play an important role to understand turbulence and momentum transport in free shear layers. The characteristic nature of this type of flow has attracted the focus of many scientists within the past century, and a large body of literature describes the dynamics in the near-field region as well as the self-similar region. Recent investigations attempt to understand the intermediate fields, called the mixing transition or the route to self-similarity. In light of this mixing transition hypothesis for jets, an apparent gap is recognized among the scientific community with two main conjectures being put forth. First, the flow will always asymptotically reach a fully self-similar state if boundary conditions permit. The second proposes partial and local self-similarity within the mixing transition. In the present work we address this topic with an experimental investigation of the intermediate-field turbulence dynamics in a nonconfined free jet with a nozzle diameter of 12.7 mm. The outer-scale Reynolds number is 15 000, and high-speed particle image velocimetry is used to record the velocity fields with a final spatial resolution of 194 × 194 µm2. The analysis focuses on higher-order moments and two-point correlations of velocity variances in space and time. We observe interactions among turbulent structures that show local self-similarity and partial coherence.

Model validation using CFD-grade experimental database for NGNP Reactor Cavity Cooling Systems with water and air

The Reactor Cavity Cooling System (RCCS) is a key safety system for the Next Generation Nuclear Plant (NGNP) gas-cooled thermal reactor to reliably transfers the core decay heat to the environment under all accident situations. Both a water-cooled and an air-cooled design have been proposed for the RCCS. Both RCCS design options consist of a set of pipes/ducts built into the reactor cavity and facing the reactor pressure vessel (RPV). Coolant (water or air, depending on the design option) flowing into the RCCS pipes removes the heat from the RPV by radiation and/or convection. The RCCS is designed to provide long term cooling of the RPV and protect the cavity structure from overheating. Both air-cooled and water-cooled RCCS are designed to operate in a passive mode during accidents, providing heat removal from the RPV and the reactor cavity using natural circulation. Several of the fundamental modeling challenges associated with the RCCS are common with the passive safety systems of Gen-III+ LWRs and integral small modular reactors (SMRs). For example, three-dimensional mixing dominated by buoyancy in the air-cooled RCCS plena and flashing-induced flow instabilities in the water-cooled RCCS risers are fundamental modeling issues common to most passive decay heat removal systems with small to modest driving pressure differences. We propose to use advanced innovative instrumentation to build a high-resolution experimental database and to use the novel experimental data to assess and further develop the predictive capabilities of both 1D thermal-hydraulic system codes and computational fluid dynamics (CFD) computer codes. We plan to investigate specific thermal-hydraulic issues, which will ensure that the RCCS is able to successfully accomplish its safety functions under all conditions, and will result in improved computational methodologies for the prediction of the RCCS behavior. The improved models proposed here will also have the direct benefit of improving the predictive capability of the passive systems of Gen-III+ LWRs and SMRs passive systems. The project objectives are to (a) provide an improved understanding of the behavior of the water-cooled RCCS during two-phase flow natural circulation operation, leveraging an existing RCCS experimental facility operated at University of Wisconsin-Madison; (b) provide improved physical insight of the mixing and stratification in the upper plena of the air-cooled RCCS through the design and operation of a new scaled test facility at the University of Michigan, equipped with advanced instrumentation and aimed at providing a novel detailed CFD-grade experimental database; (c) use the high resolved experimental data to advance the computational methodologies (both CFD and best-estimate thermal-hydraulic system codes) for the prediction of the RCCS behavior. The CFD-grade experimental database will be made available to the community through the NE-KAMS database currently being developed under the lead of Idaho National Laboratory (INL). The project will also support the expected operation of the RCCS.