3D Computational Fluid Dynamics Analysis Research Articles

Suppression of Combustion Oscillations in Hydrogen-Enriched Can-Type Combustors Through Fuel Staging

Abstract To achieve decarbonization in power-generating gas turbines, the technology of mixing hydrogen with natural gas is garnering significant attention. However, when blending natural gas with hydrogen, the altered combustion characteristics can lead to combustion instability in gas turbine combustors. Although fuel staging can effectively suppress combustion instability for can-type combustors, further research on mitigation strategies for hydrogen cofiring and their predictive methods is required. This study involves hydrogen cofiring experiments using a full-scale can-type combustor. Moreover, the resulting suppression of combustion instability is analyzed through fuel staging by utilizing three-dimensional (3D) computational fluid dynamics (CFD) and one-dimensional (1D) thermo-acoustic analysis. The experiments used a full-scale industrial can-type combustor with a five-around-one nozzle configuration. Hydrogen was blended with natural gas up to a volume fraction of 30%, maintaining a constant thermal power. Fuel staging was applied by controlling two out of five outer nozzles (ONs) along with the remaining three. Before the 1D thermo-acoustic analysis, the internal flame structure of the combustor was examined through 3D CFD analysis. Based on the results, a multi-input multi-output (MIMO) system was constructed for 1D thermo-acoustic analysis of the can-type combustor. The application of time delays derived from 3D CFD analysis to the 1D model revealed that differences in flame time delays across the nozzles cause combustion instability suppression observed in fuel staging.

Power generation gas turbine performance enhancement in hot ambient temperature conditions through axial compressor design optimization

The output power and efficiency of gas turbines are profoundly influenced by ambient temperatures, with higher temperatures resulting in a notable decline in power output. This issue becomes particularly critical during periods of heightened power demand in hot climates. There are two common ways to solve this problem: incorporating auxiliary systems, such as inlet air cooling, or undertaking a comprehensive redesign of the gas turbine core engine. However, these methods sometimes are costly and unfeasible, particularly in regions characterized by arid conditions or constrained budgets for engine modifications. An alternative strategy has been developed to optimize axial compressor performance in order to improve gas turbine power in high-temperature environments, through an innovative approach. This approach centers on the concept of “re-staggering” the stator blades as a retrofit upgrade for existing gas turbines, enabling an increase in compressor inlet mass flow rate while maintaining peak efficiency at 45 °C. An in-house optimization tool was developed, incorporating a genetic algorithm and artificial neural network, to ascertain the optimal configuration of the re-stagger angles. This optimization process was initially coupled with a mean-line solver and subsequently refined using a through-flow model to enhance the preliminary design. The refined compressor design was then subjected to a comprehensive 3D Computational Fluid Dynamics analysis. Additionally, “end-bend” and “elliptical leading edge” techniques were employed to sustain compressor efficiency and ensure stability across various design and off-design operating conditions. Following a thorough structural analysis, the newly designed compressors were manufactured and tested at two distinct sites in Iran (Yazd and Bampur). The measured data demonstrated the commendable performance and stability of the redesigned compressors, aligning closely with numerical predictions. Notably, the results showcased a substantial increase in gas turbine power output ranging from 7.0% to 8.0% at hot ambient conditions, all while preserving efficiency and stability. Encouragingly, the upgraded compressor also exhibited superior performance even at lower temperatures, such as 15 °C. Consequently, this uprating concept presents a practical and cost-effective solution for power plant operators seeking a significant boost in power output, especially during hot weather conditions or in arid regions prone to drought.

3D computational fluid dynamics analysis of PINI ion source back plate under high heat flux condition

Neutral Beam Injection (NBI) plays an essential role in Tokamak plasma heating and current drive. A positive ion-based NBI (PNBI) system is adopted in Steady State Superconducting Tokamak- 1 (SST-1). This PNBI system is capable of generating neutral hydrogen beam power of 1.7 MW at 55 keV. This system has a JET PINI (Positive Ion Neutral Injector) type of ion source. The Back Plate (BP) is a component of the PINI ion source. It consists of an SS 304 L magnet positioning & cover plate, and an OFE copper cooling plate. The back plate plays a vital role in removing the high heat load intercepted during beam operation. The present study describes 3D Computational Fluid Dynamics (CFD) analysis of the actual size back plate using the ANSYS version of R121. The 3D CFD analysis has been done under a 2.5 MW/m2 steady heat load incident on the OFE copper plate. Cooling water is provided in the Inlet header of the back plate with a mass flow rate of 1 kg/s at 34 °C. The analysis gives the surface temperature distribution over the OFE copper cooling plate with a maximum surface temperature of 174 °C and the average temperature is 122 °C. This result is in good agreement with High Heat Flux experimental results.

3D Computational Fluid Dynamics Analysis of a Convective Drying Chamber

The drying industry has grown considerably due to the tremendous demand for non-perishable food. Convective drying is one of the most popular equipment in the drying industry (food, chemical, pharmaceutical, etc.). One of the drawbacks of this equipment, when used for convective drying, is the non-uniformity in the final product quality. This study presents the development of a numerical model through Computational Fluid Dynamics (CFD). The drying chamber of a heat pump dryer is assessed from the perspective of drying air velocity and temperature profiles. The model was developed by solving different transport phenomena-related equations. The established methodology was set up to evaluate how the drying air velocity and temperature distribution affect the drying chamber. These results will define if there is a need to redesign it. The air velocity and temperature profile results show a need to redesign the chamber. Only trays 2, 3, and 4 are the ones that would achieve the drying of the products. The proposed solution is to implement air distributors or modify the tray positioning to make the drying air and temperature distribution homogeneous.

3D CFD simulation and analysis of transient flow in a water pipeline

Abstract A three-dimensional (3D) computational fluid dynamics (CFD) approach is developed to elaborate the water-hammer pipe flow and 3D detailed dynamic characteristics of a closing ball valve. The proposed CFD approach considers the water compressibility and the viscous sublayer, which are sometimes neglected in previous studies. Comparisons of the CFD results, the measured pressures and the one-dimensional results, demonstrate that the current 3D CFD approach better reproduces the experimental pressure oscillations while helping to visualize the associated physical processes and to further explore the 3D transient characteristics. The mean velocity distributions in the radial direction significantly change as the pipe transient progresses, which is closely associated with transient shear stress. Mean velocity variations at the valve during the closing process undergo three distinct stages: slight change, then drastic reduction, and finally slowing down. Head loss coefficient and discharge coefficient of the valve change as the valve closing time shortens.

Numerical Modelling and Experimental Validation of Twin-Screw Pumps Based on Computational Fluid Dynamics using SCORG®and SIMERICS MP+®

This paper presents a methodology for simulating screw pumps using a 3D-CFD transient approach. It is known in literature that the advantages of screw pumps in noise emission, reliability, and their capacity to work with any kind of fluid make their applications interesting for many fields. Increasing demands for high-performance screw pumps require a deep understanding of the flow field inside the machine. The investigation is performed by use of a 3D computational fluid dynamics analysis based on a single-domain structured moving mesh obtained by novel grid generation procedure through the commercial software SCORG. The real-time mass flow rate, rotor torque, pressure distribution, velocity field, and other performance indicators including the indicated power were obtained from numerical simulations performed in the SimericsMP+ environment. The performance curves of the numerical model were produced for variable rotation speeds and discharge pressures and compared with experimental data with high accuracy. The pressure distribution in the screw groove is relatively uniform, the screw clearance and the meshing area pressure are different from the screw groove pressure distribution. The results demonstrate that the speed does not have a considerable effect on the pressure field. At last, the numerical model was validated by comparing the numerical results with the measured performance obtained in the experimental test rig through the comprehensive experiment performed for a set of discharge pressures and rotational speeds. The model has shown to predict pressure variation and flow rate with good accuracy.

An Interim Report on Predicting Pressure Rise due to the Thermal Expansion of Trapped Liquids in Subsea Oil and Gas Equipment

Summary The objective of the present work is to propose a methodology to predict pressure rise due to the thermal expansion of trapped liquids using computational fluid dynamics (CFD). The present study also provides a comparison between the various methods used for pressure buildup calculations that are widely used in oil and gas industries. A comparison of standard thermodynamic calculations with transient 3D CFD analysis reveals that transient CFD analyses can provide deeper insights on the temperature and velocity fields in trapped volumes. The application of the proposed method is not just restricted to a single component/equipment in the subsea field but can be applied to any trapped volume in subsea equipment. In the present study, the pressure buildup in a downhole (DH) port of a subsea Christmas tree (XT) is presented for demonstration purposes; the same methodology can be extended to other equipment or regions of interest. Because of a lack of literature on the topic of pressure rise due to thermal expansion of trapped fluids, engineers are forced to make several assumptions without knowing the effect of each term or parameter on the final pressure calculated. In this study, the percentage change/variation of the final pressure using the various forms of a standard analytical pressure rise equation is also discussed in detail.

3D CFD analysis of the performance of oblique and composite side weirs in converging channels

Conventional rectangular side weirs installed along prismatic open-channels may have low efficiency. One practical way to overcome this problem may be to insert the weir in the oblique side of a converging channel. In this paper, the performance of oblique straight side weirs or two-segment single-cranked side weirs inserted in rectangular converging channels are analysed through 3D computational fluid dynamics (CFD) for subcritical steady flow conditions. The numerical simulations were performed through a widely available software package by applying the VOF method to the Reynolds-averaged Navier–Stokes equations and adopting the Reynolds stress model for turbulence closure. The model is validated against experimental data previously obtained by the authors. The results provide insight into the features of the flow field and show the effect of the channel contraction rate on diversion efficiency. As regards the two-segment single-cranked weir, the “concave” arrangement has been verified as being more efficient than the “convex” one.

Analysis Methods for High Energy Line Break Jet Flows in Nuclear Power Plants

Abstract The effects of postulated accidents, including dynamic effects of pipe ruptures, must be analyzed for licensing of nuclear power plants (NPPs). Applicants and licensees of NPPs have struggled to address U.S. Nuclear Regulatory Commission (NRC) expectations to assess if high energy line break (HELB) jet impingement on structures and components can lead to dynamic amplification, and to accurately simulate blast wave-induced loadings. In this paper, evaluation of the potential for load amplification and occurrence of resonance conclusively demonstrates that the phenomenon does not occur. In a HELB, several physical parameters of jets issuing from a ruptured pipe—such as nonequilibrium condensation of steam, unsteady separation between the jet exit and target, nonorthogonal alignment of jet axis to impingement surface, uneven impingement surfaces, or mismatch of jet excitation frequency and target natural frequency—prevent occurrence of the phase lock conditions needed to initiate and maintain a resonance. The analytical approach to evaluate the blast wave-induced loading applied a pressure vessel burst (PVB) correlation instead of performing computational fluid dynamics (CFD) analysis for all break locations. Three-dimensional (3D) CFD analysis of blast wave transient propagation provided the basis to develop benchmarking factors for use with the PVB correlation. The simplified methodology utilizes shockwave reflection, shape, and environment factors for application to impacted targets, which significantly reduces the amount of time to evaluate all break locations. The modified PVB method is also more appropriate than an explosion-type correlation to model the blast wave pressures from steam pipe breaks.

Computational Fluid Dynamics-Based Throughflow Analysis of Transonic Flows in Steam Turbines

Abstract A computational fluid dynamics (CFD)-based throughflow solver is applied to the meridional analysis of low-pressure steam turbine modules. The throughflow code inherits its numerical scheme from a state-of-the-art CFD solver (TRAF code) and incorporates real gas capabilities, three-dimensional flow features, and spanwise mixing models. Secondary flow effects are introduced via a concentrated vortex model. Tip gap and shroud leakage effects are modeled in terms of source vectors in the system of governing equations. The impact of part-span shrouds and snubbers are accounted for, on a local basis, through suitable body force fields. The advection upstream splitting method (AUSM+-up) upwind strategy has been adopted as a basis to construct a numerical flux scheme explicitly suited for throughflow applications. The original formulation has been adapted to handle real gas flows and to embed the treatment of body force fields in a fully consistent framework. The capability of the procedure is assessed by analyzing the low-pressure modules of two large steam turbines designed and manufactured by Ansaldo Energia. These modules include rotor tip shrouds and part-span snubbers and feature supersonic flow and large blade twist. Throughflow predictions in terms of main performance figures and radial distributions of flow quantities are compared with experimental data and 3D steady viscous analyses. It will be shown how the proposed CFD-based throughflow model can be fruitfully used in the early stages of the design as it delivers predictions of comparable accuracy with 3D CFD analyses at a fraction of the computational time.

Solar Salt Latent Heat Thermal Storage for a Small Solar Organic Rankine Cycle Plant

Abstract The design of the latent heat thermal storage system (LHTESS) was developed with a thermal capacity of about 100 kW h as a part of small solar plant based on the organic Rankine cycle (ORC). The phase change material (PCM) used is solar salt with the melting/solidification temperature of about 220 °C. Thermophysical properties of the PCM were measured, including its phase transition temperature, heat of fusion, specific heat, and thermal conductivity. The design of the thermal storage was finalized by means of the 3D computational fluid dynamics analysis. The thermal storage system is modular, and the thermal energy is delivered with the use of thermal oil, heated by Fresnel mirrors. The heat is transferred into and from the PCM in the casing using bidirectional heat pipes, filled with water. A set of metallic screens are installed in the box with the pitch of 8–10 mm to enhance the heat transfer from heat pipes to the PCM and vice-versa during the charging and discharging processes, which take about 4 h. This work presents a numerical study on the use of metallic fins without thermal bonding as a heat transfer enhancement method for the solar salt LHTESS. The results show that the absence of the thermal bonding between fins and heat pipes (there was a gap of 0.5 mm between them) did not result in a significant reduction of charging or discharging periods. As expected, aluminum fins provide better performance in comparison with steel ones due to the difference in the material conductivity. The main advantage observed for the case of using aluminum fins was the lower temperature gradient across the LHTESS.

Modenas CT115s performance enhancement by redesign internal geometry to improve the flow pattern of air box

This paper reviews a study of engine performance MODENAS CT15s by redesign internal geometry to improve flow pattern of air box. Air box is an empty chamber on the inlet of most combustion engines combustion process. It collects air from outside and feeds it to the intake hoses of each cylinder. The entire air box collects the fresh air and later gets it filtered through the air filter present inside it. Engine can be easily breathing related to flow pattern by best design of air box that can contribute to performance. Flow pattern of air box affect the volumetric efficiency, mass flow rate and velocity which ultimately makes impact up on the engine power & torque. 3D Computational Fluid Dynamics (CFD) analysis was carried out for an existing model and several improvement models to make comparison of air flow behaviour through the air box geometry. Based on the results, geometrical changes like sigle blade placement in inlet plenum showed good improvement in flow behaviour compare to existing model. By using 3D CFD analysis, the best design of the air box for a motorcycle engine is achieved with considerable reduction in development time and cost.

A methodology for the prediction of back-pressure induced stall in eductor-jet pumps

Eductor-jet pumps are used to transfer large quantities of fluids using a high-pressure fluid source without the need for moving parts, such as motors and impellers. The pump operates by creating the Venturi effect inside a convergent-divergent nozzle. These pumps can stall when a back pressure develops at the outlet. In this paper, the critical condition at which the stall occurs is determined by comparing the thrust force from the jets of the pump to the opposing force caused by backpressure at the pump outlet. This methodology predicts the stall conditions for both over-expanded and under-expanded flow conditions. The motive gas pressure and the backpressure ratios at which stall occurs is dependent upon the pump geometry, fluid properties, and the pump operating conditions. Experiments conducted on a 3D printed and a commercially available pump, as well as 3D computational fluid dynamics analyses, enabled verification of the proposed methodology.

Computational Fluid Dynamics Investigation of a Core-Mounted Target-Type Thrust Reverser—Part 1: Reverser Stowed Configuration

During the second half of the 90 s, NASA performed experimental investigations on six novel thrust reverser (TR) designs; core-mounted target-type thrust reverser (CMTTTR) design is one of them. To assess the CMTTTR efficiency and performance, NASA conducted several wind tunnel tests at sea level static (SLS) conditions. The results from these experiments are used in this paper series to validate the computational fluid dynamics (CFD) results. This paper is part one of the three-part series. Parts 1 and 2 discuss the CMTTTR in stowed and deployed configurations; all analyses in the first two papers are performed at SLS conditions. Part 3 discusses the CMTTTR in the forward flight condition. The key objectives of this paper are: first, to perform the three-dimensional (3D) CFD analysis of the reverser in stowed configuration; all analyses are performed at SLS condition. The second objective is to validate the acquired CFD results against the experimental data provided by NASA (Scott, C. A., 1995, “Static Performance of Six Innovative Thrust Reverser Concepts for Subsonic Transport Applications: Summary of the NASA Langley Innovative Thrust Reverser Test Program,” NASA—Langley Research Centre, Hampton, VA, Report No. TM-2000-210300). The third objective is to verify the fan and overall engine net thrust values acquired from the aforementioned CFD analyses against those derived based on one-dimensional (1D) engine performance simulations. The fourth and final objective is to examine and discuss the overall flow physics associated with the CMTTTR under stowed configuration. To support the successful implementation of the overall investigation, full-scale 3D computer aided design (CAD) models are created, representing a fully integrated GE-90 engine, B777 wing, and pylon configuration. Overall, a good agreement is found between the CFD and test results; the difference between the two was less than 5%.

CFD analysis of effects on fluid flow resistance of metallic wavy structures

Microscale wrinkles can be utilized to enhance the characteristics of products. For example, a shark skin having riblet surface can move faster underwater, minimizing fluid flow resistance. We introduce a novel approach to fabricate microscale metallic wrinkles using a soft lithography and electroforming process; we also evaluated the effects of wrinkles by computational fluid dynamics (CFD) analyses. For the generation of metallic wrinkles, a UV-curable resin, NOA68T was used to fabricate a master wrinkling pattern by mechanism of compressive forces on a skin of the weakly polymerized resin layer. The master pattern was molded and replicated as metallic wrinkles on a surface via soft lithography and electroforming processes. To understand the advantages of a wavy surface on reduction of flow resistance, we carried out two- and three-dimensional (2D and 3D) CFD analyses. The drag coefficient of a wrinkled 2D square model was decreased about 17.1 %, and a 3D real wrinkle model showed 4.9 to 7.3 % reduction of it compared to without wrinkle models. We believe that it is possible to reduce the fluid flow resistance using wavy surfaces that can easily be generated selectively or wholly on an arbitrary surface.

Performance evaluation of air flow and thermal comfort in the room with Wind-Catcher using different CFD techniques under neutral Atmospheric Boundary Layer

Energy usage in buildings using conventional Heat Ventilation Air Conditioning (HVAC) systems can be considerably reduced on using natural ventilation systems like wind catcher. In addition to high energy consumptions in conventional HVAC, other disadvantages include ozone layer depletion due to CFCs emitted and also cost involved in installation and maintenance. Purpose of this study was to investigate the airflow and thermal comfort analyses of existing common wind catcher design in the city of Yazd using computational fluid dynamics (CFD) technique. In order to have more realistic analysis, neutral homogenous atmospheric boundary layer (ABL) was created at the inlet. Standard k-e turbulence model was used since equations for creating ABL were more related to this model. 3D CFD analysis was performed using both ANSYS FLUENT and OPENFOAM. Thermal comfort analysis was evaluated based on ASHRAE standard 55.

A 3D CFD Simulation and Analysis of Flow-Induced Forces on Polymer Piezoelectric Sensors in a Chinese Liquors Identification E-Nose.

Chinese liquors can be classified according to their flavor types. Accurate identification of Chinese liquor flavors is not always possible through professional sommeliers’ subjective assessment. A novel polymer piezoelectric sensor electric nose (e-nose) can be applied to distinguish Chinese liquors because of its excellent ability in imitating human senses by using sensor arrays and pattern recognition systems. The sensor, based on the quartz crystal microbalance (QCM) principle is comprised of a quartz piezoelectric crystal plate sandwiched between two specific gas-sensitive polymer coatings. Chinese liquors are identified by obtaining the resonance frequency value changes of each sensor using the e-nose. However, the QCM principle failed to completely account for a particular phenomenon: we found that the resonance frequency values fluctuated in the stable state. For better understanding the phenomenon, a 3D Computational Fluid Dynamics (CFD) simulation using the finite volume method is employed to study the influence of the flow-induced forces to the resonance frequency fluctuation of each sensor in the sensor box. A dedicated procedure was developed for modeling the flow of volatile gas from Chinese liquors in a realistic scenario to give reasonably good results with fair accuracy. The flow-induced forces on the sensors are displayed from the perspective of their spatial-temporal and probability density distributions. To evaluate the influence of the fluctuation of the flow-induced forces on each sensor and ensure the serviceability of the e-nose, the standard deviation of resonance frequency value (SDF) and the standard deviation of resultant forces (SDFy) in y-direction (Fy) are compared. Results show that the fluctuations of Fy are bound up with the resonance frequency values fluctuations. To ensure that the sensor's resonance frequency values are steady and only fluctuate slightly, in order to improve the identification accuracy of Chinese liquors using the e-nose, the sensors in the sensor box should be in the proper place, i.e., where the fluctuations of the flow-induced forces is relatively small. This plays a significant reference role in determining the optimum design of the e-nose for accurately identifying Chinese liquors.

Power Consumption and Temperature Distribution in WRGB Active-Matrix OLED Displays

In this paper, the power consumption of a white-red-green-blue (WRGB) active-matrix organic light-emitting device (OLED) display and the resulting temperature distribution across the display are analyzed as a function of the applied image and the luminance of the emitted light. It has been shown previously that temperature directly impacts the picture quality of an OLED display. Luminance, spectral radiance, power and temperature measurements are performed on a 55-in WRGB OLED display with a resolution of 1920 ×1080. A power model is presented that allows calculating the display's power consumption for a given applied image. This involves the dependency of the efficiency of the white OLED on the current density, the wavelength dependent transmission of the color filters and the contribution of each of the subpixels in producing the display's nominal white. The output of the power model is used as input for a basic thermal model that simulates the temperature distribution across the display. The thermal model is based on 3D computational fluid dynamics analysis framework (FloEFD). A good agreement between the simulations and measurements on the sample WRGB OLED display is obtained.

Performance validation of a large scale helium turboexpander for cryogenic applications through CFD analysis

The demand of low temperature for superconducting magnets used in high energy physics applications has necessitated the need for helium refrigeration and liquefaction cycles with improved efficiency. Any attempt of designing a plant with improved thermodynamic performance may call for improvement of efficiency of turboexpanders. Developing a design strategy for helium turboexpander with better efficiency demands in depth understanding of the complex flow physics. Computational Fluid Dynamics (CFD) is a useful tool to find the details of the flow and evolve a design strategy leading to improved performance of the machine. In the present work, 3D CFD analysis of a large scale cryogenic helium turboexpander designed and tested at BARC was performed using Ansys CFX®. Different aspects of computation procedure such as turbulence models, and models for rotor stator interface have been discussed. Results obtained from simulation were compared with experimental results for validation.

Coupled RELAP5, 3D CFD and FEM analysis of postulated cracks in RPVs subjected to PTS loading

The fracture mechanic analysis of a reactor pressure vessel subjected to pressurized thermal shock loading is one of the most important issues for the assessment of life time extension of a nuclear power plant. The most severe scenario occurs during cold water injection in the cold leg due to a Loss-Of-Coolant Accident (LOCA). In the present study a comprehensive fracture mechanics analysis is performed. Two hypothetical LOCAs are assumed for an adopted reference design of a two-loop Pressurized Water Reactor. Boundary conditions obtained from the RELAP5 code are used as input for Computational Fluid Dynamics (CFD) simulations. For the structural integrity analysis, submodeling technique and the eXtended Finite Element Method (XFEM) based on temperatures calculated by CFD are applied. The results from the 3D FEM calculations are compared to those from a simplified axisymmetric model based on axisymmetric thermal hydraulic model results. The analysis identifies the worst crack orientation and location. It also proves that a complete model is needed for a correct analysis as the simplified model is not conservative and fails to describe accurately the local plume effect.