In this paper, a numerical simulation of three-dimensional motion of tether undersea kites (TUSK) for power generation is studied. TUSK systems includes a rigid-winged kite, or glider, moving in an ocean current in which a tethered kite is connected by a flexible tether to a fixed structure. Kite hydrodynamic forces are transmitted through the tether to an electrical generator on the fixed structure. The numerical simulation models the flow field in a three-dimensional domain near the rigid undersea kite wing by solving the full Navier-Stokes equations. In order to resolve the boundary layer near the kite surface, adequate grid resolution is needed which increases the computational run time drastically especially in 3D simulations. Therefore, in this study a slip boundary condition is implemented at the kite interface to accurately predict the total drag, with lower grid resolution. In order to reduce the numerical run times, a moving computational domain method is also used. A PID controller is used to adjuste the kite pitch, roll and yaw angles during power (tether reel-out) and retraction (reel-in) phases. A baseline simulation study of a full-scale TUSK system is conducted in which the expected cross-current, figure-8 motions during a kite reel-out phase is captured. The effect of the tether drag on the kite motion and resulting power output is also investigated and compared with the results of the baseline simulation.

Optimized operation of gas turbines is discussed for a fleet of eleven LM2500PE engines at a Statoil North Sea offshore field i n Norway. Three engines are generator drivers whilst eight engines are compressor drivers. Several of the compressor drive engines are running at peak load (T5.4 control), hence the production rate is limited by the available power from these engines. The majority of the engines discussed run continuously without redundancy, hence gas turbine uptime is critical for the field’s production and economy. Two of the compressor drive engines are instrumented with a new static P2 probe in order to have an inlet depression measurement and thus be able to monitor compressor air flow. Compressor air flow has been used as an additional parameter to efficiency, in order to have better analysis methods and better documentation of deterioration rates. The performance gain with online water wash at high water-to-air ratio and upgraded inlet air filter systems, as well as successful operation at longer intervals between offline wash/maintenance stops are thus documented. An approach for developing a compressor map for mass flow based on field measurements, predictions and deterioration has been performed, as well as correction methods for engine load and ambient conditions in order to be able to compare performance points in various conditions and engine control modes. When monitoring compressor air flow, the Reynolds number effects on axial compressor performance can be analyzed. Understanding the gas turbine performance deterioration is of vital importance. Trending of its deviation from the engine baseline facilitates load-independent monitoring of the gas turbine’s condition. Instrument resolution and repeatability are key factors in order to have reasonable results on the performance analysis. Based on previous tests and analysis, the compressor air flow rate is the most sensitive parameter for detecting performance deterioration. Unfortunately, gas turbines for offshore operation, are normally not equipped with any air flow measurement devices.

The traditional organic Rankine cycle (ORC) is operated below critical point. However, the specific heat of the working fluid undergoes tremendous change near the critical point. This can improve the thermal performance of the system due to the enhancement of heat transfer coefficient within the heat exchanger. However, the strong temperature dependence of thermo-physical properties of the working fluid especially at near the critical point requires much more efforts in designing a heat exchanger. Hence, more elaborate calculation involving stepwise integration is needed as far as accuracy is concerned. Therefore the heat exchanger is divided into several segments. The outlet temperatures of the first segment serve as the input parameters for the second segment, and the process is carried out further on. The fluid properties are calculated with the actual bulk temperature of each segment. With increasing number of segments, better resolution of temperature distribution of both heat source and working fluid within the heat exchanger is achieved. In the present study, a plate heat exchanger was numerically examined by using R-245fa as a working fluid at a supercritical condition. The effects of the working pressure and mass flow rate were examined in detail. For all cases in this study, the maximum of the total heat transfer rate was achieved by a working pressure of 3700 kPa, especially close to critical pressure. It is found that at a working pressure of 4000 kPa and mass flow rate ranging from 1 kg/s to 1.75 kg/s, the total heat transfer rate was independent of the mass flow rate.

A series of experiments were performed on a vertical EV burner with a constant coflow air of 873 L /min to generate turbulent lean premixed flow in order to study the impact of the addition of Acetylene/Argon mixture to the liquefied petroleum gas (LPG) on the temperature field and flame structure. The fluidics mechanism was inserted at a fixed position inside the entry section of the EV burner assembly. The flow rates of fuel (LPG/C 2 H 2 / Ar) and air were measured using calibrated rotameters. The different volume ratios of the fuel constituents (at a specified fuel flow rate) were admitted via three solenoid valves at the entry section of each stream prior to mixing and monitored using a labview program. The axial temperature profiles at different operating conditions were measured using a bare wire Pt-Pt -10% Rh (type S) thermocouple of wire diameter 250 μm. Flame images were obtained — before and after fluidics insertion — using a high resolution Canon 6D 20MP digital camera. The selection of the different considerated cases was based on flame stability. The experimental program aims at identifying and analyzing the changes in flame characteristics (flame length, axial profiles of mean gas temperature, NOx concentration and overall combustion efficiency) resulting from the insertion of fluidics while considering different proportions of the fuel constituents) (including pure LPG, as a reference case). In all experiments flame stabilization was ensured. The results obtained indicate the following: it was noticed that in most cases of pure LPG only, and other mixtures the images shows increase in both the length and luminosity of the flame as a result of higher degrees of swirl due to the fluidics insertion while the temperature profiles of the different flames were changed. It was indicated that NOx trend was decreased by 52% while the combustion efficiency was improved by 2.5%.

The influence of mesh resolution, the abilities of various eddy viscosity models, and near wall flow treatments on predicting the flow coefficients of poppet valves, operating in water are investigated in this paper. The computational fluid dynamics (CFD) models are solved using STAR-CCM+ 12.04. Grid-convergence is studied first, followed by quantitative assessments of the ability of standard k-ε model, realizable k-ε model, EB k-ε model, Lag EB k-ε model, V2F model and k-ω-sst model, and different wall treatments, such as high y + wall treatment, two-layer wall treatment and all y + wall treatment, embedded in the solver. The flow discharge coefficient (C q ) of poppet valves predicted by CFD models are compared to physical measurements. It was demonstrated in the study that grid resolutions normal to the wall and mesh quality are key factors. Advanced near wall flow treatments produce similar or worse predictions when using the standard k-ε model, and the effects of the near wall flow treatments are marginal for the realizable k-ε model. The ability of turbulence models varies greatly in predicting flow in different valves and lift levels. The realizable k-ε model is the optimal option for the considered valve flows giving an acceptable error within ±5%.

A dynamic modeling study and field validation of a cooling tower serving a chiller are performed in this study to evaluate the efficiency of the cooling tower under various conditions. The dynamic model examines the losses and thermal capability of the cooling tower. The cooling tower used in this study for field validation is located at Cookeville, Tennessee, USA. The whole setup is fully instrumented to record the water and air flow rates and temperature; make-up water and blow down water flow rates; power consumption of pump; fan and chiller; weather data; etc. with one-hour resolution. The outcomes of the model are validated with the recorded data of the cooling tower and the test condition data. Furthermore, the effects of using Variable Frequency Drive (VFD) on the cooling tower’s fan power consumption are investigated. Additional recommendations on improving the energy efficiency and reducing the water losses are suggested based on the modeling data.

In this paper, a numerical simulation of three dimensional motion of tether undersea kites (TUSK) for power generation is studied. TUSK systems consist of a rigid-winged kite, or glider, moving in an ocean current. One proposed concept uses a tethered kite which is connected by a flexible tether to a support structure with a generator on the ocean surface. The numerical simulation models the flow field in a three-dimensional domain near the rigid undersea kite wing by solving the full Navier-Stokes equations. A two-step projection method along with Open Multi-Processing (OpenMP) is employed to solve the flow equations. In order to track the rigid kite, an immersed boundary method is used. A NACA 0021 airfoil is used for the cross section shape of the kite, and the tension forces in the elastic tethers are modeled by a simple Hooke’s law. A grid refinement study has been carried out to ensure the independence of the numerical results on the grid mesh resolution. Also, the Reynolds number independency has been studied. PID control methods are used to adjust the kite pitch, roll and yaw angles during power (tether reel-out) and retraction (reel-in) phases to obtain desired kite trajectories. During the reel-out phase the kite moves in successive cross-current motions in a figure-8 pattern, the tether length increases and power is generated. During reel-in the kite motion is along the tether, and kite hydrodynamic forces are reduced so that net positive power is produced. Kite trajectories, hydrodynamic forces on the kite, kite tether tension and output power are determined and analyzed for a baseline TUSK simulation.

The research of multiple liquefied natural gas fires is limited due to the unique condition of temperature and velocity. Therefore, the effect of the distance between multiple liquefied natural gas jet fires on the characteristics of the flame is investigated by numerical methods in this paper. Grid analyses have been carried out to establish sufficient resolution of the grid and to ensure the domain size is appropriate for jet fire cases. The temperature, velocity and concentration of the reactant inside the fire were calculated, and the shape of the flame was also studied. By changing the distance between the jets, the size and height of the fires are changed. Simulations of jet fires separated by different distances were carried out. Investigation of three discharge velocities (30, 40, 50 m/s) with different separation distances (0–28 m) were done. When the jets were close enough fires were observed to merge and were enhanced due to interaction. Both the flame height and the temperature increased. When the jets were separated by a significant distance, the flame height returned to the height of a single jet fire. The distance effect of multiple jet fires was investigated and reported in this paper.

The objective of this study is to examine the impact of single and multi-component surrogate fuel mixtures on the atomization and mixing characteristics of non-reacting isothermal diesel engine sprays. An Eulerian modeling approach was adopted to simulate both the internal nozzle flow dynamics and the emerging turbulent spray in the near nozzle region in a fully-coupled manner. The Volume of Fluids (VoF) methodology was utilized to treat the two-phase flow dynamics including a Homogenous Relaxation approach to account for nozzle cavitation effects. To enable accurate simulations, the nozzle geometry and in-situ multi-dimensional needle lift and off-axis motion profiles have been characterized via the X-ray phase-contrast technique at Argonne National Laboratory. The flow turbulence is treated via the classical k –ϵ Reynolds Average Navier Stoke (RANS) model with in-nozzle and near field resolution of 30 μm. Several multi-component surrogate mixtures were implemented using linear blending rules to examine the behavior of petroleum, and alternative fuels including: JP-8, JP-5, Hydro-treated Renewable Jet (HRJ), Iso-Paraffinic Kerosene (IPK) with comparison to single-component n-dodecane fuel on ECN Spray A nozzle spray dynamics. The results were validated using transient rate-of-injection measurements from the Army Research Laboratory at Spray A conditions as well as projected density fields obtained from the line-of-sight measurements from X-ray radiography measurements at The Advanced Photon Source at Argonne National Laboratory. The conditions correspond to injection pressure, nominal fuel temperature, and ambient density of 1500 bar, 363 K, and 22.8 kg/m 3 , respectively. The simulation results provide a unique high-fidelity contribution to the effects of fuels on the spray mixing dynamics. The results can lead to improvements in fuel mixture distributions enhancing performance of military vehicles.

Pressure Locking and Thermal Binding (PL/TB) are two different but related physical phenomena, which under certain conditions may prevent the opening of some types of valves. According to the US Nuclear Regulatory Commission (NRC) NPP operators should evaluate all safety.related power operated gate valves in all operational configurations for susceptibility to PL/TB. Corrective actions are required for susceptible valves that shall assure performance of safety function within plant licensing bases. NEK (NEK) first addressed this issue through the analysis of the Motor Operated Valves (MOV) that were included in the NEK MOV program. This approach resulted with 31 valves in Krško NPP being found as susceptible to TB, 21 of which to both TB and PL. Subsequently, a more thorough analysis was performed, which took into account realistic operational parameters and detailed deterministic and probabilistic assessment evaluation of accident scenarios. This produced a list of 8 valves susceptible to PL, and another 8 susceptible to TB. Valves were screened according to their safety significance, safety function, type, operational history, and operational conditions. Where applicable, Probabilistic Safety Analysis (PSA) has been used as a tool to screen the risk from PL/TB to the safe plant operation. To reduce the risk from PL/TB occurrence, either physical modification of the valve (alteration of actuator gear ratio to provide more force), relevant part of the entire fluid system (flooding of sump suction lines), or simulation and testing to confirm actual ability to overcome increased forces (initiating a controlled TB condition, and testing to confirm actuator’s ability to perform), was used. Methods used and results produced for TB are the subject of this paper.

The emergency core cooling system (ECCS) and containment spray system (CSS) in a pressurized water reactor (PWR) are designed to safely shutdown the plant following a loss of coolant accident (LOCA). The assurance of long term core cooling in PWRs following a LOCA has a long history dating back to the NRC studies of the mid 1980s associated with Unresolved Safety Issue (USI) A-43. Results of the NRC research on boiling water reactor (BWR) ECCS suction strainer blockage of the early 1990s identified new phenomena and failure modes that were not considered in the resolution of USI A-43. As a result of these concerns, Generic Safety Issue (GSI) 191 was identified in September 1996 related to debris clogging of the ECCS sump suction strainers at PWRs. Although plants have taken steps to prevent strainer clogging (by increasing the screen area, for example), satisfactory closure of this issue has proved elusive due to long term cooling issues and the effect of chemical precipitates on head loss. Previous investigators have identified bounding scenarios using conservative inputs, methods, and acceptance criteria. The acceptance criteria are applied in a “pass/fail” fashion that ignores risk. That is, if the results are acceptable, the issue has been resolved. Otherwise, it is necessary to either redo the analysis with partial relaxation of analytical conservatisms or perform additional plant modifications to ensure that the acceptance criteria are met. This article describes a new approach to close out the GSI-191 issue by evaluating the risk associated with ECCS performance on post-LOCA core cooling as a basis to change the plant license. The approach includes an assessment of LOCA frequencies as a function of break size at locations along the reactor coolant system, as well as a full quantification of the uncertainties associated with LOCA frequencies and the generation, transport, accumulation, and subsequent impact of debris on ECCS performance. The overall frameworks for the deterministic and risk-informed approaches are summarized with emphasis on the risk-informed method. The differences between the deterministic approach taken in the past and the new risk-informed approach are described. Advantages and disadvantages between the two methods are described and contrasted for the GSI-191 issue. The South Texas Project (STP) GSI-191 risk-informed closure efforts are presented.

Integranular cracking is among the most notable material degradation processes in operating nuclear power plants. Examples include intergranular stress corrosion cracking of austenitic steels and nickel based alloys and irradiation assisted stress corrosion cracking of stainless steel baffle bolts. Recent advances in computational methods and computational resources facilitated development of multiscale computational methods with increasing degrees of realism, stemming mostly from the explicit treatment of randomly shaped and oriented anisotropic grains. Such methods can simulate the polycrystalline aggregates of a few hundred or even thousand grains and are receiving increasing support from the non-destructive experimental techniques such as for example X-ray diffraction contrast tomography. Further development of increasingly realistic multiscale simulation methods requires resolution of some modeling issues. These include reliable, accurate and numerically efficient modeling of the progressive damage along the grain boundaries. Critical appraisal of a number of possible approaches to model the progressive damage along the grain boundaries represents the core of the proposed paper.

Pressure Locking and Thermal Binding (PL/TB) are two different but related physical phenomena, which under certain conditions may prevent the opening of some types of valves. According to the US Nuclear Regulatory Commission (NRC) NPP operators should evaluate all safety-related power operated gate valves in all operational configurations for susceptibility to PL/TB. Corrective actions are required for susceptible valves that shall assure performance of safety function within plant licensing bases. NEK (NEK) first addressed this issue through the analysis of the Motor Operated Valves (MOV) that were included in the NEK MOV program. This approach resulted with 31 valves in Krško NPP being found as susceptible to TB, 21 of which to both TB and PL. Subsequently, a more thorough analysis was performed, which took into account realistic operational parameters and detailed deterministic and probabilistic assessment evaluation of accident scenarios. This produced a list of 8 valves susceptible to Pressure Locking, and another 8 susceptible to TB. Valves were screened according to their safety significance, safety function, type, operational history, and operational conditions. Where applicable, Probabilistic Safety Analysis (PSA) has been used as a tool to screen the risk from PL/TB to the safe plant operation. To reduce the risk from PL/TB occurrence, either physical modification of the valve (alteration of actuator gear ratio to provide more force), relevant part of the entire fluid system (flooding of sump suction lines), or simulation and testing to confirm actual ability to overcome increased forces (initiating a controlled PL condition, and testing to confirm actuator’s ability to perform), was used. Methods used and results produced for PL are the subject of this paper.

Investigations on gas-liquid flows in horizontal pipes are of immanent importance for Reactor Safety Research. In case of a breakage of the main cooling circuit of a Pressurized Water Reactor (PWR), the pressure losses of the gas-liquid flow significantly govern the loss of coolant rate. The flow regime is largely determined by liquid and gas superficial velocities and contains slug flow that causes high-pressure pulsations to the infrastructure of the main cooling circuit. Experimental and numerical investigations on adiabatic slug flow of a water-air system were carried out in a horizontal pipe of about 10 m length and 54 mm diameter at atmospheric pressure and room temperature. Stereoscopic high-speed Particle Image Velocimetry in combination with Laser Induced Fluorescence was successfully applied on round pipe geometry to determine instantaneous three-dimensional water velocity fields of slug flows. After grid independence studies, numerical simulations were run with the open-source CFD program OpenFOAM. The solver uses the VOF method (Volume of Fluid) with phase-fraction interface capturing approach based on interface compression. It provides mesh refinement at the interfacial area to improve resolution of the interface between the two phases. Furthermore, standard k-ε turbulence model was applied in an unsteady Reynolds averaged Navier Stokes (URANS) model to resolve self-induced slug formation. The aim of this work is to present the feasibility of both relatively novel possibilities of determining two-phase slug flows in pipes. Experimental and numerical results allow the comparison of the slug initiation and expansion process with respect to their axial velocities and cross-sectional void fractions.

Draper Laboratory has developed a prototype, automated system that measures on-line loss-on-ignition (LOI) in coal power plants. The system automatically extracts fly ash samples via a sample probe inserted into the flue gas stream and delivers them to an integrated thermo-gravimetric-analyzer (TGA) that analyzes the sample’s LOI according to the ASTM C311 standard. The integrated TGA is custom designed and built to be rugged and low cost relative to a laboratory grade instrument and can analyze samples every fifteen minutes. This LOI sensor is a major improvement in time and spatial resolution over the commonplace method of sampling fly ash from the bag house and sending it offsite for analysis. During field tests at actual power plants, the prototype system acquired ash samples and analyzed them while unattended. A proposed redesign for commercialization is also described.

The NURESIM and NURISP successive projects of the 6 th and 7 th European Framework Programs joined the efforts of 21 partners for developing and validating a reference multi-physics and multi-scale platform for reactor simulation. The platform includes system codes, component codes, and also CFD or CMFD simulation tools. Fine scale CFD simulations are useful for a better understanding of physical processes, for the prediction of small scale geometrical effects and for solving problems that require a fine space and/or time resolution. Many important safety issues usually treated at the system scale may now benefit from investigations at a CFD scale. The Pressurized Thermal Shock is investigated using several simulation scales including Direct Numerical Simulation, Large Eddy Simulation, Very Large Eddy Simulation and RANS approaches. At the end a coupling of system code and CFD is applied. Condensation Induced Water-Hammer was also investigated at both CFD and 1-D scale. Boiling flow in a reactor core up to Departure from Nucleate Boiling or Dry-Out is investigated at scales much smaller than the classical subchannel analysis codes. DNS was used to investigate very local processes whereas CFD in both RANS and LES was used to simulate bubbly flow and Euler-Lagrange simulations were used for annular mist flow investigations. Loss of Coolant Accidents are usually treated by system codes. Some related issues are now revisited at the CFD scale. In each case the progress of the analysis is summarized and the benefit of the multi-scale approach is shown.

The one dimensional two-fluid model is widely acknowledged as the most detailed and accurate macroscopic formulation model of the thermo-fluid dynamics in nuclear reactor safety analysis. Currently the prevailing one dimensional thermal hydraulics codes are first order accurate. The benefit of first order schemes is numerical viscosity, which serves as a regularization mechanism for many otherwise ill-posed two-fluid models. However, excessive diffusion in regions of large gradients leads to poor resolution of phenomena related to void wave propagation. In this work, a second order numerical method is developed for a standard two-fluid model code by applying a second order temporal scheme and a shock capturing scheme using a flux limiter formulation for the convection of void fraction and velocity. The classic water faucet problem is taken as the benchmark.

In order to balance the resolution and the total computational effort in turbulent combustion CFD code COM3D, a block structured local mesh refinement has been introduced. In the presented work, special attention has been given to the implementation of local mesh refinement for the alternative directions based method and time-operator splitting approach. An application of the implemented technique for the detonation simulations is examined and discussed.

This paper summarizes the analysis of loss of coolant accident (LOCA) frequencies in support of a risk-informed (RI) evaluation of Generic Safety Issue (GSI) 191 for the South Texas Project Electric Generating Station (STPEGS) Units 1 and 2. The STP RI-GSI 191 Closure Study investigates the size and location of loss of coolant accidents (LOCAs) more finely than in traditional PRAs in order to assess the risk of debris formation during the LOCAs that could interfere with the operation of the emergency core cooling systems (ECCSs) or inhibit coolant flow through the core during the recirculation phase after a LOCA. The size and location of the break could influence the amount and chemistry of debris formation and the timing and need for actions to initiate or terminate containment sprays and recirculation cooling. This application requires the capability to estimate LOCA frequencies as a function of break size at each location within the Class 1 pressure boundary with due regard to the proper characterization and quantification of uncertainties.

Void fraction is one of important physical values for gas-liquid two-phase flow in nuclear power plants, and it is an essential parameter for designs and performance evaluations of devices, including a core of BWR and so on. Therefore void fraction measurement with real time, high temporal resolution and high spatial resolution has been needed. In several void fraction measurement methods, electric measurement methods of void fraction can realize real-time measurement. In previous studies, conductance methods capacitance methods, wire mesh methods and tomography techniques have been studied. In the present study, we research on a constant electric current method. This method can measure void fraction with higher temporal resolution and simpler systems. In previous study, the constant electrical current method has been applied in annular flow mainly. However, the method cannot be applied to three dimensional dispersed bubbly flow. This is because void fraction is estimated by cross-section ratio of gas and liquid phases in this method. In the present study, Maxwell’s theory and polarization method are applied to calculation method of void fraction from voltage measured by constant electrical current method, and we try to measure void fraction in dispersed bubbly flow. Maxwell’s theory is a calculation of a mixture with two materials of different conductivity. The polarization method proposed in this study assumes bubbles to be dielectric bodies and void fraction is estimated by the polarization electric field of the bubbles. In the experimental results, the void fractions in the three dimensional dispersed bubbly flow can be estimated with Maxwell’s theory and the polarization method. The void fractions estimated with these methods are more accurately than the previous method. Furthermore, it is experimentally clarified that the present proposed method can follow highly temporal void fluctuations of bubbly and froth flows. In addition, effects of intervals between electrodes and structures of electrodes are experimentally investigated.