The accurate prediction of heat fluxes and, thus, metal wall temperatures of gas turbine (GT) combustor liners is a complicated and numerically expensive task. Computational Fluid Dynamics (CFD) support for the design of cooling systems is essential to ensure safe and proper operation of the entire gas turbine engine. Indeed, it is well known how complicated, and, at the same time, expensive it is to carry out experimental campaigns inside combustors operating under working conditions, and, therefore, pressurized and having high temperatures. The correct prediction of thermal fluxes in a CFD simulation depends on the proper modeling of all the involved phenomena and their interactions with each other. For this reason, Conjugate Heat Transfer (CHT) simulations are mandatory in gas turbine cooling system applications. Multiphysics and multiscale simulations, based on loosely-coupled approaches, have emerged as extremely effective numerical tools, providing enormous computational time sav... [more]

Bladeless fans are more energy efficient, safer due to the hidden blades, easier to clean, and more adjustable than conventional fans. This paper investigates the influence of the airfoil’s outlet slit thickness on the discharge ratio by varying the outlet slit thickness of an Eppler 473 airfoil from 1.2 mm to 2 mm in intervals of 0.2 mm by using a k-omega SST turbulence model with an all y+ wall treatment used to numerically simulate in CFD. The computational results indicated that smaller slits showed higher discharge ratios. The airfoil with a 1.2 mm slit thickness showed a discharge ratio of 18.78, a 24% increase from the discharge ratio of the 2 mm slit. The effect of outlet angle on the pressure drop across the airfoil was also studied. Outlet angles were varied from 16° to 26° by an interval of 2°. The airfoil profile with a 24° outlet angle showed a maximum pressure difference of 965 Pa between the slit and leading edge. In contrast, the 16° outlet angle showed the least pressu... [more]

In order to better understand the complex pooling and vaporization of a liquid hydrogen spill, Sandia National Laboratories is conducting a highly instrumented, controlled experiment inside their Shock Tube Facility. Simulations were run before the experiment to help with the planning of experimental conditions, including sensor placement and cross wind velocity. This paper describes the modeling used in this planning process and its main conclusions. Sierra Suite’s Fuego, an in-house computational fluid dynamics code, was used to simulate a RANS model of a liquid hydrogen spill with five crosswind velocities: 0.45, 0.89, 1.34, 1.79, and 2.24 m/s. Two pool sizes were considered: a diameter of 0.85 m and a diameter of 1.7. A grid resolution study was completed on the smaller pool size with a 1.34 m/s crosswind. A comparison of the length and height of the plume of flammable hydrogen vaporizing from the pool shows that the plume becomes longer and remains closer to the ground with increa... [more]

Modeling IT equipment is of critical importance for the simulations of flow and thermal structures in air cooled data centers. Turbulent flow undergoes a significant pressure drop through the server due to the energy losses originating from the internal components. Therefore, there is an urgent need to develop a fast and an accurate method for the calculation of pressure losses inside server components for data center applications. In this study, high resolution numerical simulations were performed on an OCP (Open Compute Project) server under various inlet flow rates for inactive and active conditions. Meanwhile, one key challenge of modeling complete geometry of the server results from using an intense mesh even for a single server. To address this challenge, the server was modeled as a porous zone to mimic inertia and viscous resistance in a realistic way. Comparison of the results of porous and complete models showed that the proposed model could calculate pressure drop accurately... [more]

A printed circuit heat exchanger (PCHE) is utilized to cool the compressor inlet air to increase the compression efficiency in a liquid air energy storage and liquid natural gas (LNG) coupled system, which can offer large-scale energy storage with significantly improved exergy efficiency and round-trip efficiency. In this work, the effect of pressure of air, incline angle, and hydraulic diameter on the performance of a compressed air−water PCHE with a semicircle cross-section was studied. The results show that PCHE can realize the intermediate cooling of air compression in the liquid air energy storage system, and the pressure variation of air shows a limited effect on the heat transfer of PCHE; however, the hydraulic diameter and the incline angle both affect the heat transfer and the flow resistance of PCHE, and the best incline angle is 15°.

This paper presents a numerical analysis of the stability of the flow parameters along the intake duct of an aircraft jet turbine engine. This problem has been investigated by many research teams and was included in the literature analysis. The unstable operation of a turbojet intake system can be the consequence of many adverse factors, including an intake vortex. The investigated intake system, due to its low location to the plane of the airport, is highly susceptible to the formation of an intake vortex. The phenomenon of an intake vortex can, in the worst-case scenario, result in the surging of the turbojet, and even engine stalling. This paper presents a developed model of the forward section of an aircraft, complete with its intake duct, and the method of its discretization. The intake-system model and numerical analysis were performed in Ansys Fluent. The flow parameters adopted for numerical simulations, under specific boundary conditions, corresponded to the operating conditio... [more]

On the path towards climate-neutral future mobility, the usage of synthetic fuels derived from renewable power sources, so-called e-fuels, will be necessary. Oxygenated e-fuels, which contain oxygen in their chemical structure, not only have the potential to realize a climate-neutral powertrain, but also to burn more cleanly in terms of soot formation. Polyoxymethylene dimethyl ethers (PODE or OMEs) are a frequently discussed representative of such combustibles. However, to operate compression ignition engines with these fuels achieving maximum efficiency and minimum emissions, the physical-chemical behavior of OMEs needs to be understood and quantified. Especially the detailed characterization of physical and chemical properties of the spray is of utmost importance for the optimization of the injection and the mixture formation process. The presented work aimed to develop a comprehensive CFD model to specify the differences between OMEs and dodecane, which served as a reference diesel... [more]

In this work, a novel ejector design concept of a swirl-bypass nozzle is proposed to improve off-design performance of CO2 two-phase ejectors. The swirl-bypass nozzle allows part of the flow to bypass into the ejector mixing chamber to generate swirl. The design of such a device is investigated using a 3D multiphase CFD model. An extensive experimental test campaign is conducted to validate the baseline homogeneous equilibrium CFD model. The model’s prediction motive mass flow rate within 2−12% error and suction mass flow rate was predicted with 3−50% error. Based on the tested ejector geometry, simulations of different ejector swirl-bypass inlets are conducted. The results show that, for the current design, total entrainment of the ejector is reduced by 2−20% with the swirl-bypass inlet. The axial position of the bypass inlet plays a primary role in the bypass inlet flow rate, and, consequently, in suction flow reduction. This is found to be due to the bypass flow blocking off the suc... [more]

China−Myanmar oil and gas pipelines in Southwest China guarantee the energy security of China. Due to poor geographical circumstances, the safety of pipelines is seriously threatened by natural disasters. Therefore, there is a crucial, practical significance to establishing a model of leakage and diffusion of crude oil in the mountainous terrain and to conduct related applied studies. In the present study, computational fluid dynamic simulations of the dynamic diffusion process of leaking contaminants on the mountain surface was performed; the influence of the pipe pressure, landform, surface environment and leakage location on diffusion speed and range were discussed carefully. The results indicate that the variation of topographic altitude determines the path of leaking contaminants. Accordingly, an improved algorithm based on the SFD8 algorithm to predict the path of leaking contaminants at a low leakage rate was proposed; this would be instructive for an emergency response to ensur... [more]

Crosswind action on a train poses a risk of vehicle overturning or derailment. To assess if new train designs fulfill the safety requirements, computational fluid dynamics is commonly used. This article presents a comprehensive wind flow analysis on an example of a TGV high-speed train. Large yaw angle range is studied with the application of widely used Reynolds-averaged Navier−Stokes (RANS) turbulence models. The predictive performance of popular RANS-based models in that regime has not been reported extensively before. The context of simulations is a study of crosswind stability using methodology presented in norm EN 14067-6:2018. It is shown that for yaw angles up to 45 degrees, aerodynamic forces predicted by all the studied RANS-based models are consistent with experimental data. At larger yaw angles, flow structure becomes complicated, separation lines are no longer defined by geometry, and significant discrepancies between turbulence models appear, with relative differences bet... [more]

Worldwide need for renewable energy sources increases significantly with the drastic negative greenhouse effects of climate change. This study considers a water-cooled hybrid thermo-electric panel (PV/T) which contributes to better harvesting of solar energy. A numerical CFD model was developed for power generation of a standard PV panel as well as for a water-based PV/T system laminated with polymer matrix composite (PMC) materials, and user-defined functions (UDFs) were developed and integrated with the CFD model to implement exact boundary conditions. Experimentation under daily weather conditions was carried out in order to validate the numerical CFD model by measuring the surface temperatures of PV and PV/T systems as well as the temperatures of the water inlet and outlet of the cooling system. The results show that the maximum and minimum deviations of the surface temperature between numerical and experimental studies matched well compared with the studies performed in the litera... [more]

This article deals with the numerical simulation of unsteady cavitating flow around hydrofoils, supported by experimental research realized in a cavitation tunnel situated in the Centre of Hydraulic Research. Two straight NACA hydrofoils (NACA0020 and NACA2412) were employed. The comprehensive unsteady CFD analysis was based on scale-resolving simulations (hereinafter SRS) with the aim of capturing correctly the interactions between the cavitation structures and re-entrant flow as well as the compressibility and thermal effects of cavitation. The static pressure fluctuations during the cavity oscillation cycles and the evaporation and condensation processes are discussed in detail. To predict correctly the high-pressure peaks during the bubble cloud collapses and the pressure pulse propagation speed, the real properties of water and the mixture total energy conservation equation were considered. In addition, the estimated content of undissolved air was taken into account. The numerical... [more]

Hydropower is a key source of electricity production for allowing the integration of intermittent renewable energy resources. Among the various hydraulic power plants around the world, the ones equipped with Pelton turbines already provide large flexibility that is still enhanced with the development, for instance, of the hydraulic short circuit operating mode. However, the knowledge of the flow inside Pelton turbines is still a challenging task, both numerically and experimentally, despite progress in the last two decades. One key feature of the Pelton efficiency is the jet quality, i.e., the jet velocity needs to be uniform, not perturbed by secondary flows and compact. The compactness of the jet is mainly dependent o nthe location of the jet detachment at the nozzle outlet, which is challenging for computational fluid dynamics simulations mainly due to numerical diffusion. Even if this point has already been mentioned in previous papers, the present paper focuses on all the paramete... [more]

The adjoint method is a very promising gradient-based optimisation framework for computational fluid dynamics (CFD), because of its independence of the computation cost from the number of design variables. With the aim of improving the robustness of the continuous adjoint topology optimization, this paper presents a direct method for the design variable update. Based on the intrinsic feature of the topology optimization, this straightforward update method explicitly controls the design variable target volume, precluding any case-dependent parameters. The details of its implementation are discussed with regard to an existing open-source continuous adjoint topology optimization solver. The performance of this alternative method is tested on complex 3D engineering problems with duct configuration, and no impact on the computational demands or numerical stability has been observed in the simulations.

The adjoint method is a very promising gradient-based optimisation framework for computational fluid dynamics (CFD), because of its independence of the computation cost from the number of design variables. With the aim of improving the robustness of the continuous adjoint topology optimization, this paper presents a direct method for the design variable update. Based on the intrinsic feature of the topology optimization, this straightforward update method explicitly controls the design variable target volume, precluding any case-dependent parameters. The details of its implementation are discussed with regard to an existing open-source continuous adjoint topology optimization solver. The performance of this alternative method is tested on complex 3D engineering problems with duct configuration, and no impact on the computational demands or numerical stability has been observed in the simulations.

For propulsion systems using gel fuels, reducing the gel fuel viscosity is essential for achieving better atomization and combustion. In this paper, we investigate the flow and heat transfer in a water-gel with a temperature and shear dependent viscosity. We consider several different channels, mimicking the transport of gelled fuels in propulsion systems, and we also look at corrugation, which is a way of enhancing fluid mixing and thus improving the heat transfer characteristics. The rheological parameters in the constitutive model of the gel are fitted with experimental data. The influence of different corrugation profiles, corrugation configuration parameters and the Reynolds number on the mean apparent viscosity and the pressure drop are investigated. It was found that the flow recirculation formed in the valley of the corrugations enhances the heat transfer and thus the temperature of the main flow. We also noticed an increase in the pressure drop due to the stronger viscous diss... [more]

To study the relationship between sediment concentration and the performance parameters of centrifugal pumps, Jiamakou water supply pumping station with total installed capacity of 30,880 kW was selected to analyze characteristics of the centrifugal pump in this paper. Based on a CFD mixture model, the effects of different sediment concentrations on the movement of solid−liquid two-phase flow and the performance parameters of the centrifugal pump were obtained. Then, fitting equations were established between performance parameters (head, flow rate, shaft power, and efficiency) of the centrifugal pump and sediment concentration at three working conditions (0.8 Q = 2 m3/s, Q = 2.5 m3/s, 1.2 Q = 3 m3/s) by the polynomial least-square method. Calculated values of fitting equations were compared with the measured values in centrifugal pump operation. The results show that, as the sediment concentration increases from 0.1% to 1%, the maximum volume fraction of sediment at blade outlet incre... [more]

Horizontal axis wind turbines are used for energy generation at domestic as well as industrial levels. In the wind turbines, a reduction in drag force and an increase in lift force are desired to increase the energy efficiency. In this research work, computational fluid dynamics (CFD) analysis has been performed on a turbine blade’s frontal section with an NACA S814 profile. The drag force has been reduced by introducing an array of dimpled structures at the blade surface. The dimpled structures generate a turbulent boundary layer flow on its surface that reduces the drag force and modifies the lift force because it has greater momentum than the laminar flow. The simulation results are verified by the experimental results performed in a wind tunnel and are in close harmony with the simulated results. For accurate results, CFD is performed on the blade’s frontal section at the angle of attack (AOA) with a domain of 0° to 80° and at multiple Reynolds numbers. The local attributes, lift f... [more]

For the past decade, research on vertical axis wind turbines (VAWTs) has garnered immense interest due to their omnidirectional characteristic, especially the lift-type VAWT. The H-rotor Darrieus VAWT operates based on the lift generated by aerofoil blades and typically possesses higher efficiency than the drag-type Savonius VAWT. However, the open-ended blades generate tip loss effects that reduce the power output. Wingtip devices such as winglets and endplates are commonly used in aerofoil design to increase performance by reducing tip losses. In this study, a CFD simulation is conducted using the sliding mesh method and the k-ω SST turbulence model on a two-bladed NACA0018 VAWT. The aerodynamic performance of a VAWT with offset, symmetric V, asymmetric and triangular endplates are presented and compared against the baseline turbine. The simulation was first validated with the wind tunnel experimental data published in the literature. The simulation showed that the endplates reduced... [more]

The conventional method of optimizing the aerodynamic performance of an airfoil heavily depends on the confines of the design space. The design variables create a non-normalized space that is fragmented into several different clusters of airfoils. An approach that is data-driven and deforms airfoils over a Grassmannian submanifold is utilized in the work that is being presented here. The affine deformation, which includes camber and thickness, can be uncoupled from the method that is currently in use, and the operations that are performed on the airfoil shape can be made smooth enough to prevent unreasonable shapes from being produced. The CST method is also a part of the current study so that a comparison can be made between the two. A new method to describe the airfoil geometries over the Grassmannian space was generated using a dataset that contained 7007 different shapes of airfoils. These two methods are used to parameterize the subsonic (NACA0012) and transonic (RAE2822) airfoils... [more]

Periodic open cellular structures (POCS) are becoming increasingly popular as catalyst carriers due to favorable properties: mixing flow, intense heat/mass transfer and low flow resistance. Their design and manufacturing are relatively easy and cheap. The presented paper focuses on the characterization of POCS in relation to their definition, types, classification and properties. Next, the design and manufacturing methods are described. Finally, the literature review dealing with the application of POCS in catalytic processes are presented.

The design and optimization of photobioreactor(s) (PBR) benefit from the development of robust and quantitatively accurate computational fluid dynamics (CFD) models, which incorporate the complex interplay of fundamental phenomena. In the present work, we propose a comprehensive computational model for tubular photobioreactors equipped with glass sponges. The simulation model requires a minimum of at least three submodels for hydrodynamics, light supply, and biomass kinetics, respectively. First, by modeling the hydrodynamics, the light−dark cycles can be detected and the mixing characteristics of the flow (besides the mass transport) can be analyzed. Second, the radiative transport model is deployed to predict the local light intensities according to the wavelength of the light and scattering characteristics of the culture. The third submodel implements the biomass growth kinetic by coupling the local light intensities to hydrodynamic information of the CO2 concentration, which allows... [more]

Safety issues arising from a hydrogen explosion accident in Korea are discussed herein. In order to increase the safety of hydrogen refueling stations (HRSs), the Korea Gas Safety Corporation (KGS) decided to install a damage-mitigation wall, also referred to as a barrier, around the storage tanks at the HRSs after evaluating the consequences of hypothetical hydrogen explosion accidents based on the characteristics of each HRS. To propose a new regulation related to the barrier installation at the HRSs, which can ensure a proper separation distance between the HRS and its surrounding protected facilities in a complex city, KGS planned to test various barrier models under hypothetical hydrogen explosion accidents to develop a standard model of the barrier. A numerical simulation to investigate the effect of the recommended barrier during hypothetical hydrogen explosion accidents in the HRS will be performed before installing the barrier at the HRSs. A computational fluid dynamic (CFD) c... [more]

The increasing importance of renewable energy capacity in the power generation scenario, together with the fluctuating consumer energy demand, forces conventional fossil fuel power generation systems to promptly respond to relevant and rapid load variations and to operate under off-design conditions during a major fraction of their lives. In order to improve existing power plants’ flexibility in facing energy surplus or deficit, retrofittable solutions for gas turbine compressors are proposed. In this paper, two different operation strategies, variable inlet guide vanes (IGVs) and blow-off extraction (BO), are considered for enabling partial load and minimum environmental load operation, and thus to identify implementation opportunities in existing thermal power plants. A typical 15-stage F-class gas turbine compressor is chosen as a test case and some energy demand scenarios are selected to validate the adopted solutions. The results of an extensive 3D, steady, CFD analysis are compar... [more]

CFD modeling of an innovative wave energy device has been carried out in this study. OpenFoam wave modeling solver interFoam has been employed in order to investigate the energy extraction capability of the wave energy device. The innovative concept is based on utilizing the pressure differential under the crest and trough of a wave to drive flow through a pipe. The simulated surface elevation of a wave has been validated against the reported wave tank experimental data in order to provide confidence in the modeling outcome. Further, simulations have been carried out with the device placed near to the bottom of the numerical wave tank in order establish the energy extraction potential. The simulation results confirm that effective power can be generated from the wave energy device. The efficiency of the device decreases with the increase in wave height, although it increases with the wave period. Higher power-take off (PTO) damping is also beneficial in extracting increased energy from... [more]