CFD simulations of turbulent buoyant atmospheric flows over complex geometry: Solver development in OpenFOAM

2018 ◽

Author(s):

Dilesh Maharjan ◽

Mustafa Hadj-Nacer ◽

Miles Greiner ◽

Stefan K. Stefanov

Keyword(s):

Heat Transfer ◽

Rarefied Gas ◽

Complex Geometry ◽

Direct Simulation Monte Carlo ◽

Accurate Method ◽

Vacuum Drying ◽

Helium Pressure ◽

Two Dimensional ◽

Dsmc Method ◽

Cfd Simulations

During vacuum drying of used nuclear fuel (UNF) canisters, helium pressure is reduced to as low as 67 Pa to promote evaporation and removal of remaining water after draining process. At such low pressure, and considering the dimensions of the system, helium is mildly rarefied, which induces a thermal-resistance temperature-jump at gas–solid interfaces that contributes to the increase of cladding temperature. It is important to maintain the temperature of the cladding below roughly 400 °C to avoid radial hydride formation, which may cause cladding embrittlement during transportation and long-term storage. Direct Simulation Monte Carlo (DSMC) method is an accurate method to predict heat transfer and temperature under rarefied condition. However, it is not convenient for complex geometry like a UNF canister. Computational Fluid Dynamics (CFD) simulations are more convenient to apply but their accuracy for rarefied condition are not well established. This work seeks to validate the use of CFD simulations to model heat transfer through rarefied gas in simple two-dimensional geometry by comparing the results to the more accurate DSMC method. The geometry consists of a circular fuel rod centered inside a square cross-section enclosure filled with rarefied helium. The validated CFD model will be used later to accurately estimate the temperature of an UNF canister subjected to vacuum drying condition.

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Unsteady Simulations of a Low NOx LDI Combustor for Environmentally Responsible Aviation Engines

Volume 4B: Combustion, Fuels and Emissions ◽

10.1115/gt2015-43802 ◽

2015 ◽

Author(s):

Scott A. Drennan ◽

Gaurav Kumar ◽

Erlendur Steinthorsson ◽

Adel Mansour

Keyword(s):

Experimental Data ◽

Complex Geometry ◽

Mesh Refinement ◽

Operating Conditions ◽

Design Parameters ◽

Nox Emissions ◽

Fuel Injector ◽

Cfd Simulations ◽

Wide Range ◽

Environmentally Responsible

A key objective of NASA’s Environmentally Responsible Aviation (ERA) research program is to develop advanced technologies that enable 75% reduction of LTO NOx emissions of N+2 aviation gas turbine engines relative to the CAEP 6 standard. To meet this objective, a new advanced multi-point fuel injector was proposed and tested under the NASA ERA program. The new injector, called the three-zone injector, or 3ZI, uses fifteen spray cups arranged in three zones. Swirling air flows into each cup and fuel is introduced via pressure swirl atomizers within the cup. Multiple design parameters impact the performance of the injector, such as the location of the atomizer within the spray cup, the spray angle and cup-to-cup spacing. To fully understand the benefits and trade-offs of various injector design parameters and to optimize the performance of the injector, detailed CFD simulations are an essential tool. Furthermore, the CFD methodology must allow easy changes in design parameters and guarantee consistent and comparable accuracy from one design iteration to the next. This paper investigates the use of LES in reacting and non-reacting flows and compares against the NOx experimental data for the multi-point atomization strategy of the injector. The CFD simulations employ an automatically generated Cartesian cut-cell meshing approach with mesh refinement applied near complex geometry and spray regions. Adaptive Mesh Refinement (AMR) is used to refine mesh in regions of high gradients in velocity and temperature. The CFD simulations use boundary and operating conditions based on experimental data for air flow and spray atomization obtained from LDV and PDPA characterizations of the spray respectively. The results are extended to reacting flow using a detailed reaction mechanism and predictions of NOx emissions are compared to experimental data. Overall NOx predictions were consistently less than experimental values. However, the NOx prediction trends showed excellent agreement with experimental data across the wide range of equivalence ratios investigated.

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Efficiency and Critical Velocity Analysis of Gravitational Separator Through CFD Simulation

Volume 7: Fluids Engineering ◽

10.1115/imece2017-71230 ◽

2017 ◽

Cited By ~ 5

Author(s):

Haiwen Zhu ◽

Jianjun Zhu ◽

Jiecheng Zhang ◽

Hong-Quan Zhang

Keyword(s):

Oil And Gas ◽

Cfd Simulation ◽

Complex Geometry ◽

Separation Efficiency ◽

Liquid Velocity ◽

Effective Parameters ◽

Cfd Simulations ◽

Associated Gas ◽

Separation Velocity ◽

Critical Separation

Oil and gas producing rates have increased rapidly with the development of shale oil and fracturing technology. Besides, advances in horizontal wells have increased the slugging issue, especially in complex geometry wells. Therefore, Artificial lift systems, especially rod-pumps and electrical submersible pumps, always suffer from associated gas and require an economical way to avoid problems like gas lock, gas pound, gas interference and slugging. Among all kinds of the downhole separator, and the gravitational separator are the most economical devices, which can handle severe slugging problems. The rule of thumb liquid maximum downward velocity for the gravitational separator is 0.6 in/s [13, 14]. However, the criterion needs to be improved by considering pressure, temperature and fluid properties. This article first uses CFD simulations to validate the critical liquid velocity and then obtains pressure field, velocity profile, gas distribution and sensitivity factors under complicated field situations. The results could be used to develop an empirical or even a mechanistic efficiency prediction model in the future. In this paper, 2-D simulation is first utilized to study the critical separation velocity and effective parameters. Comparing with Stokes’ law, the simulation shows density, and surface tension have a strong effect of critical separation velocity, while viscosity has lower influence. Then extended 2-D simulations are conducted on different inner tube to annulus connection geometry, which shows a strong effect on separation efficiency. Later on, 3-D CFD simulations are generated based on a newly designed separator by TUALP and an existing design from the Don-Nan separator. Simulations are used to validate 2-D conclusion and illustrate the improvement of the new design.

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CFD Analysis of Compressible Flow Across a Complex Geometry Venturi

Journal of Fluids Engineering ◽

10.1115/1.2754321 ◽

2007 ◽

Vol 129 (9) ◽

pp. 1193-1202 ◽

Cited By ~ 2

Author(s):

Diego A. Arias ◽

Timothy A. Shedd

Keyword(s):

Compressible Flow ◽

Discharge Coefficient ◽

Static Pressure ◽

Complex Geometry ◽

Three Dimensional ◽

Turbulent Model ◽

Cfd Simulations ◽

Pressure Losses ◽

Computational Fluid Dynamics Cfd ◽

Fuel Tube

A commercial computational fluid dynamics (CFD) package was used to develop a three-dimensional, fully turbulent model of the compressible flow across a complex-geometry venturi, such as those typically found in small engine carburetors. The results of the CFD simulations were used to understand the effect of the different obstacles in the flow on the overall discharge coefficient and the static pressure at the tip of the fuel tube. It was found that the obstacles located at the converging nozzle of the venturi do not cause significant pressure losses, while those obstacles that create wakes in the flow, such as the fuel tube and throttle plate, are responsible for most of the pressure losses. This result indicated that an overall discharge coefficient can be used to correct the mass flow rate, while a localized correction factor can be determined from three-dimensional CFD simulations in order to estimate the static pressure at locations of interest within complex venturis.

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