Efficiency Optimization of a 30MW Main Boiler Feedwater Pump Using CFD and Scaled Model Tests

A “credible” computational fluid dynamics (CFD) model has the potential to provide a meaningful evaluation of safety in medical devices. One major challenge in establishing “model credibility” is to determine the required degree of similarity between the model and experimental results for the model to be considered sufficiently validated. This study proposes a “threshold-based” validation approach that provides a well-defined acceptance criteria, which is a function of how close the simulation and experimental results are to the safety threshold, for establishing the model validity. The validation criteria developed following the threshold approach is not only a function of Comparison Error, E (which is the difference between experiments and simulations) but also takes in to account the risk to patient safety because of E. The method is applicable for scenarios in which a safety threshold can be clearly defined (e.g., the viscous shear-stress threshold for hemolysis in blood contacting devices). The applicability of the new validation approach was tested on the FDA nozzle geometry. The context of use (COU) was to evaluate if the instantaneous viscous shear stress in the nozzle geometry at Reynolds numbers (Re) of 3500 and 6500 was below the commonly accepted threshold for hemolysis. The CFD results (“S”) of velocity and viscous shear stress were compared with inter-laboratory experimental measurements (“D”). The uncertainties in the CFD and experimental results due to input parameter uncertainties were quantified following the ASME V&V 20 standard. The CFD models for both Re = 3500 and 6500 could not be sufficiently validated by performing a direct comparison between CFD and experimental results using the Student’s t-test. However, following the threshold-based approach, a Student’s t-test comparing |S-D| and |Threshold-S| showed that relative to the threshold, the CFD and experimental datasets for Re = 3500 were statistically similar and the model could be considered sufficiently validated for the COU. However, for Re = 6500, at certain locations where the shear stress is close the hemolysis threshold, the CFD model could not be considered sufficiently validated for the COU. Our analysis showed that the model could be sufficiently validated either by reducing the uncertainties in experiments, simulations, and the threshold or by increasing the sample size for the experiments and simulations. The threshold approach can be applied to all types of computational models and provides an objective way of determining model credibility and for evaluating medical devices.

Aerodynamic characteristics of a guided rocket projectile are numerically simulated. Simulations are performed in a range of flight conditions using a commercial CFD software FLUENT, and variations of lift coefficients and drag coefficients with Mach numbers and angles of attack were demonstrated. The numerical results also indicate that the angle of canard deflection has significant influence on the flow field near tailfins.

Three-dimensional flow phenomena have been observed in a shock tube experiment for shock waves and vortices by using an interferometric CT (Computed Tomography) technique with a N2 pulse laser. A model with small duct, which has a pair of circular open ends, is introduced in a test section of diaphragmless shock tube, and can be rotated around its central axis to change the observation angle. The projection image of density distribution for each observation angle is obtained by using a fixed Mach-Zehnder interferometer. Three-dimensional density distribution is reconstructed from these projection images. The shock Mach number is 2.3 in nitrogen gas of 19.4kPa initial pressure at the exits of the open ends. The resultant 3-D density flow fields are illustrated by several imaging technique to clarify 3-D features of shock waves, vortices, and their mutual interactions. A computational fluid dynamics (CFD) simulation is also applied to the 3-D flow fields. The CFD results can represent density and another properties in flow fields, and these properties are useful for identifying the phenomena. The mutual validation between the experimental CT density results and these CFD results is discussed. Three-dimensional features of flow fields are investigated in detail by analyzing the experimental CT results with CFD results.

Establishment and validation of a relationship model between nozzle experiments and CFD results based on convolutional neural network

A 3-step global reaction mechanism for a methane-air mixture is optimized against a detailed reference mechanism for perfectly stirred reactor (PSR) calculations. The global mechanism consists of three reactions corresponding to the fuel oxidation into CO and H2O, and the CO–CO2 equilibrium reaction. To ensure good agreement for rich conditions, correction functions that are dependent on the local equivalence ratio are introduced into the global mechanism. In a comparison of the optimized 3-step global reaction mechanism with the reference detailed reaction mechanism, GRI Mech 3.0, the results show that the gas temperature and emissions are reasonably well predicted for lean and rich conditions. The optimized 3-step global reaction scheme is adapted in the Computational Fluid Dynamics (CFD) analysis of a swirl-stabilized syngas burner, designed by Siemens Industrial Turbomachinery (SIT syngas burner) for gas turbines. The burner consists of a main premixed flame, a partially premixed pilot flame and a confined rich premixed lean flame which produces radicals that support both the pilot and the main flame. The CFD results are compared with experimental results obtained in an atmospheric version of the burner test rig at Lund University. Both steady-state Reynolds Averaged Navier Stokes (RANS) and hybrid Unsteady RANS/Large Eddy Simulation (URANS/LES) results were computed. The CFD results with the 3-step global reaction mechanism show good agreement with the experimental data on gas analysis and flame visualization, while the Westbrook Dryer 2-step (WD2) [2] and Meredith et al. [3] 3-step global reaction mechanisms failed in their predictions of the CO emissions downstream in the burner.

Computational fluid dynamic (CFD) simulations in support of the SHARP-B2 (Slender Hypervelocity Aerothermodynamic Research Probes) program are presented. Pre-flight simulations of the aerothermal flight environment have been made to aid in the design of the flight hardware and instrumentation. Simulations of a critical flight qualification ground test performed in the 20 MW Panel Test Facility (PTF) arc jet, which is equipped with a semi-elliptical nozzle, have also been performed. The arc jet simulations were performed with the same CFD code that is used in the flight calculations. For both the flight and the arc jet simulations, the CFD results are used to provide surface heat transfer coefficients that serve as boundary conditions for an in-depth conduction thermal response code. By using the same CFD tool to compute the aerothermal environments for both the ground test and the flight test environment, useful comparisons are made regarding the traceability of the ground test environment to flight. Introduction The NASA Ames Research Center has been developing new Ultra High Temperature Ceramics (UHTC's) with the goal that these materials will enable sharp leading edges to be used for future space vehicles. Because of their unique thermo-structural properties, these materials are capable of operation at temperatures near 5100 °F without ablation. The materials have been developed and tested in ground-based arc jet facilities, and a flight test program designated SHARP (Slender Hypervelocity Aerothermodynamic Research Probes) has been initiated. The first flight demonstration, SHARP-B1, incorporated a UHTC nosetip mounted on a U.S. Air Force Mkl2A entry vehicle in collaboration with Sandia National Laboratory (SNL), and was successfully flown in May, 1997. The second flight test, SHARP-B2, which incorporated four instrumented UHTC strakes mounted on the side of the entry vehicle, was flown in September 2000. The goal of these flight tests is to assess the performance of the materials under entry conditions. The use of Computational Fluid Dynamic (CFD) simulations for the design of Thermal Protection Systems (TPS) has evolved to an extent that they have been integrated into the preliminary design process of Reusable Launch Vehicle (RLV) programs such as the X-33. Real-gas CFD simulations with finite-rate chemistry and proper boundary conditions for coupling with material thermal response codes are now routinely performed on high-end laboratory workstations. Much of the ground based testing of advanced TPS components is done in arc-heated test facilities such as those located in the Arc Jet Complex at the NASA Ames Research Center. These facilities are capable of simulating the high enthalpy flow environment experienced by entry vehicles for a broad range of test conditions and configurations. Semi-elliptical nozzles are available for the testing of flat panels in a high enthalpy boundary layer environment. CFD is • Aerospace Engineer, Reacting Flow Environments Branch, Member AIAA. t Senior Research Scientist, ELORET, Member AIAA. Copyright © 2001 by the American Institute of Aeronautics and Astronautics, Inc. No copyright is asserted in the United States under Title 17, U.S. Code. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental Purposes. All other rights are reserved by the copyright owner. (c)2001 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization.

The aim of this study is to investigate the use of computational fluid dynamics (CFD) in evaluating the thermal performance of a parallel/counterparallel flow heat exchanger used as part of a fluid warmer to treat hypothermia. The developed CFD model was validated in a parametric study using previously collected experimental data. The effects of heat exchanger length and inlet mass flow rate were considered. To more accurately represent the thermodynamic average temperature profile, the current CFD analysis evaluated outlet temperatures in terms of mean bulk temperature as opposed to the centerpoint temperature probe used in the experimental study. Despite this difference, the CFD results were found to agree well with the experimental values. As such, the CFD simulations are not only applicable to future design considerations but elicit further understanding of the thermal and hydrodynamic characteristics within the heat exchanger. Using the validated CFD model, thermal hydraulic entrance lengths ...

In the development of compressor, one-dimensional (1D) analysis is indispensable as it can quickly determine the basic parameters and predict characteristics of compressors. To enhance the accuracy of 1D analysis, genetic algorithms and comparison methods are used to obtain the calculation coefficients for deviation angle, work, and efficiency in the empirical models. An eight-stage axial compressor was chosen for optimization and validation. At 90% and 100% design speeds, the 1D results with applying the coefficients for deviation angle, work, and efficiency closely match the characters of the experimental data. The error in choking flow rate and peak efficiency are within 2% when compared to both experimental data and computational fluid dynamics (CFD) results. From 50% to 80% design speeds, the maximum error of 1D results with applying the coefficients for deviation angle and work in choking flow rate and peak efficiency are within 1.6% when compared to both the experimental data and CFD results. Additionally, applying these coefficients in 1D analysis also improves the prediction accuracy for compressors with variable inlet guide vanes(VIGV).

The vibration performance of centrifugal impellers is important for pumps and hydraulic excitation is a key source of vibration. The complex internal secondary flow in the centrifugal impeller brings degradation on vibration performances. An attempt of optimization by controlling the thickness distribution of centrifugal impeller blade is given to repress the internal secondary flow and alleviating vibration. The usual method of modifying an impeller on vibration performance is applying splitter blades. In this study, an ordinarily designed impeller is improved by the optimization attempt and the optimized impeller (OPT) is compared with the prototype impeller (PRT) with traditional splitter blades. The vibration performances of the impellers, the PRT, the ordinary impeller (ODN), and the OPT, are investigated numerically and experimentally. Meanwhile, further study on the influence of the thickness distribution optimization on vibration is conducted. There is a relative velocity gradient from suction side (SS) to pressure side (PS) in impeller ODN, causing nonuniformity of energy distribution. By means of thickness distribution optimization, the impeller blade angle on the PS and SS along the blade-aligned streamwise location is, respectively, modified and therefore the flow field can be reordered. The energy transfer in impeller is also redistributed after the modification of blade thickness distribution. What is more, experimental research upon impeller PRT and impeller OPT is also complemented to support the computational fluid dynamics (CFD) results. The experimental results show that the hydraulic performance of the impellers basically agree with the CFD results and the vibration data also proves a better vibration performance of the OPT.

A novel oil–water separator design and its performance prediction

The basic principle of low exergy building systems is the minimization of excess temperature gradients across building systems so that the quality of the energy supplied to the building better matches with the actual demand of the building. Several low exergy technologies which were developed at ETH, Switzerland were implemented in a small research laboratory (BubbleZERO) in Singapore to evaluate the performance of these systems for the tropics. In this paper, the indoor space conditioned by these technologies is analysed by computational fluid dynamics (CFD). Different sources of heat, water vapour and carbon dioxide have been modelled with suitable boundary conditions and emission sources., The CFD results have been verified with different numerical settings and the impact of different turbulence models and mesh densities on the accuracy of the CFD results has been studied. The results have shown that SST k-ω and Reynolds Stress turbulence models have close predictions while the standard k-e model underestimate the temperature values. In addition, indoor air quality concerns like cold feet or excessive temperature difference for occupants in the space are investigated by checking the thermal stratification in the space.

Enhancing CFD-LES air pollution prediction accuracy using data assimilation

Floodways, where a road embankment is permitted to be overtopped by flood water, are usually designed as broad-crested weirs. Determination of the water level above the floodway is crucial and related to road safety. Hydraulic performance of floodways can be assessed numerically using 1-D modelling or 3-D simulation using computational fluid dynamics (CFD) packages. Turbulence modelling is one of the key elements in CFD simulations. A wide variety of turbulence models are utilized in CFD packages; in order to identify the most relevant turbulence model for the case in question, 96 3-D CFD simulations were conducted using Flow-3D package, for 24 broad-crested weir configurations selected based on experimental data from a previous study. Four turbulence models (one-equation, k-ε, RNG k-ε, and k-ω) ere examined for each configuration. The volume of fluid (VOF) algorithm was adopted for free water surface determination. In addition, 24 1-D simulations using HEC-RAS-1-D were conducted for comparison with CFD results and experimental data. Validation of the simulated water free surface profiles versus the experimental measurements was carried out by the evaluation of the mean absolute error, the mean relative error percentage, and the root mean square error. It was concluded that the minimum error in simulating the full upstream to downstream free surface profile is achieved by using one-equation turbulence model with mixing length equal to 7% of the smallest domain dimension. Nevertheless, for the broad-crested weir upstream section, no significant difference in accuracy was found between all turbulence models and the one-dimensional analysis results, due to the low turbulence intensity at this part. For engineering design purposes, in which the water level is the main concern at the location of the flood way, the one-dimensional analysis has sufficient accuracy to determine the water level.

Pumping efficiency and rotordynamic stability are paramount to subsea multiphase pump operation since, during the life of a well, the process fluid transitions from a pure liquid to a mixture of gas in the liquid to just gas. Circumferentially grooved seals commonly serve as balance pistons in pumps while also restricting secondary flow. Prior experimental results obtained with a grooved seal operating with a mixture of air and mineral oil show the seal rotordynamic force coefficients vary significantly with the gas volume fraction (GVF). This paper, complementing an exhaustive experimental program, presents a computational fluid dynamics (CFD) analysis to predict the leakage and dynamic force coefficients of a circumferentially grooved seal supplied with air in an oil mixture with a GVF varying from 0 to 0.7. The test seal has 14 grooves, an overall axial length of 43.6 mm, and radial clearance of 0.211 mm. The 127 mm diameter rotor spins at constant angular speed (Ω = 3500 rpm). The mixture enters the seal at a supply pressure (Pin) of 2.9 bar(a), and the seal exit pressure (Pout) is 1 bar(a). The CFD two-phase flow simulations utilize the Euler–Euler multiphase model to predict the mass flowrate and the pressure field as a function of the operating conditions. Using a multi-frequency shaft orbit motion method, the CFD simulations deliver the variations of reaction force on the rotor with respect to the excitation frequency. For a pure liquid condition (GVF = 0), both the CFD and experimental results produce constant stiffness, damping, and added mass coefficients. The experimental and CFD results demonstrate the seal rotordynamic force coefficients are quite sensitive to the GVF. When introducing a small amount of air into the oil (GVF = 0.1), the direct damping coefficient increases by approximately 10%. For operation with a mixture with inlet GVF > 0.1, the cross-coupled stiffness coefficients develop strong frequency-dependent characteristics. In contrast, the direct damping coefficient has a negligible variation with excitation frequency. The CFD predictions, as well as the experimental results, evidence that air injection in a liquid stream can significantly change the seal rotordynamic characteristics, and thus can affect the rotordynamic stability of a pump. An accurate CFD analysis provides engineers to design reliable grooved seals operating under two-phase flow conditions.

A computational model is developed in order to investigate pollutant emissions from power plant boilers to the atmosphere. A well-known method of pollutant reduction is the modification of the combustion conditions to prevent their formation, and 3D computational fluid dynamics (CFD) codes provide an effective tool for the analysis of the combustion process. In this paper CFD calculations were performed to analyze the effect of the amount of combustion air on the production and emission of nitrogen oxides, one of the main pollutants produced during the combustion process. For this analysis the appropriate modeling of the chemical and physical phenomena involved is important, because the production and transport of pollutant species strongly depend on the flow and temperature distributions in the furnace. Two case studies are presented: a pulverized coal-firing tangential boiler and a fuel-oil frontal boiler. The CFD calculations adopt a 3D-formulation of the mean flow equations in combination with the standard high-Reynolds-number k-ε turbulence model. The model domain consists of the whole boiler, from the burner nozzles up to the exit of the economizer. Due to their complex geometrical features and computational limitations bank tubes are not modeled individually, but are grouped in a total volume. A porous media region approach is then undertaken to model gas flow and heat transfer in each heat exchanger. Model validation is a difficult task due to the lack of available data from commercial utilities. Validation has been done using routinely measured global parameters. Relatively good agreement is obtained. Results show that increasing the amount of air reduce nitrogen oxides formation for the case of the tangential boiler, however for the frontal boiler case this behavior is not as evident. These results demonstrate that CFD simulations are a viable tool to study the effect some combustion parameters have on the production of pollutants. CFD results may help to establish trends that, in turn, may help to reduce pollutant emissions from power plant boilers.