Abdollah Arabshahi

Investigation of Two Analytical Wake Models Using Data From Wind Farms

A code ‘Wind Farm Optimization using a Genetic Algorithm’ (referred as WFOG) was developed for optimizing the placement of wind turbines in large wind farms. It utilizes an analytical wake model (by Jensen et al.) to minimize the cost per unit power for the wind farm. In this study, a new wake model by Ishihara et al. is tested in WFOG. The wake model takes into account the effect of atmospheric turbulence and rotor generated turbulence on the wake recovery. Results of the two wake models are compared with data from Horns Rev and Nysted wind farm. The maximum error (Horns Rev wind farm) for Ishihara’s wake model was 7% as compared to 15% for Jensen’s wake model. The optimal results obtained in earlier studies (using Jensen’s wake model) are compared to wind farm configurations obtained for Ishihara’s wake model. The optimization is carried out for the simplest wind regime: Constant wind speed and fixed wind direction.Copyright

CFD Investigation of Human Tidal Breathing through Human Airway Geometry

Abstract This study compares the effect of the extra-thoracic airways on the flow through the lower airways by carrying out computational fluid dynamics (CFD) simulations of the airflow through the human respiratory tract. In order to facilitate this comparison, two geometries were utilized. The first was a realistic nine-generation lower airway geometry derived from computed tomography (CT) images, while the second included an additional component, i.e., an idealized extra-thoracic airway (ETA) coupled with the same nine-generation CT model. Another aspect of this study focused on the impact of breathing transience on the flow field. Consequently, simulations were carried out for transient breathing in addition to peak inspiration and expiration. Physiologically-appropriate regional ventilation for two different flow rates was induced at the distal boundaries by imposing appropriate lobar specific flow rates. The scope of these simulations was limited to the modeling of tidal breathing at rest. The typical breathing rates for these cases range from 7.5 to 15 breaths per minute with a tidal volume of 0.5 Liter (L). For comparison, the flow rates for constant inspiration/expiration were selected to be identical to the peak flow rates during the transient breathing. Significant differences were observed from comparing the peak inspiration and expiration with transient breathing in the entire airway geometry. Differences were also observed for the lower airway geometry. These differences point to the fact that simulations that utilize constant inspiration or expiration may not be an appropriate approach to gain better insight into the flow patterns present in the human respiratory system. Consequently, particle trajectories derived from these flow fields might be misleading in their applicability to the human respiratory system.

A New Approach to Mesh Adaptation Procedure Using Linear Elasticity for Geometries Undergoing Large Displacements

The equations of linear elasticity have been extensively used in computational fluid dynamics to deform meshes for moving boundary simulations, shape design optimization, solution adaptive refinement, and for the construction of higher-order discetizations in finite-element schemes. Inherently this method does not have any mechanism to control the quality of the mesh, since it represents the structural response to prescribed surface deflections. Unfortunately, this method does not prevent the possibility of generating negative volumes in the mesh when large deformations take place. In the current work, two approaches are examined in an attempt to mitigate this shortcoming. In the first approach, a source term is added to each node in the mesh. These source terms are chosen as design variables, and an optimization strategy is utilized to improve mesh quality. The second approach represents a modification to an existing method whereby each element in the mesh may be considered as a different material. Entries in the constitutive relations are then selected as the design variables. In this approach the number of design variables is extremely large and, thus, very computationally expense. To alleviate some of this computational burden, the design variables are selected from a subset of the elements in the mesh. In both approaches presented, the cost function is defined as a function of the mesh quality, and a limited memory BFGS optimization scheme used to minimize this function. Results for two dimensional test cases are presented; however, the concept can be easily applied to three dimensional meshes and practical problems.© 2014 ASME

Turbofan flowfield simulation using Euler equations with body forces

A method for flow computations around ducted propfans is presented. The approach is to use the body force terms in the three-dimensional Euler equations to model the propeller. Numerical solutions are compared with experimental data for three ducted propfan configurations for different flow conditions.

Enhanced legume root growth with pre-soaking in α-Fe2O3 nanoparticle fertilizer

The rising demand for food and energy crops has triggered interest in the use of nanoparticles for agronomy. Specifically, iron oxide-based engineered nanoparticles are promising candidates for next-generation iron-deficiency fertilizers. We used iron oxide and hybrid Pt-decorated iron oxide nanoparticles, at low and high concentrations, and at varied pHs, to model seed pre-soaking solutions for investigation of their effect on embryonic root growth in legumes. This is an environmentally friendly approach, as it uses less fertilizer, therefore less nanoparticles in contact with the soil. Analysis from varied material characterization techniques combined with a statistical analysis method found that iron oxide nanoparticles could enhance root growth by 88–366% at low concentrations (5.54 × 10−3 mg L−1 Fe). Hybrid Pt-decorated iron oxide nanoparticles and a higher concentration of iron oxide nanoparticles (27.7 mg L−1 Fe) showed reduced root growth. The combined materials characterization and statistical analysis used here can be applied to address many environmental factors to finely tune the development of vital nanofertilizers for high efficiency food production.

Computation of Dynamic Stability and Control Derivatives

The objective of this research is to develop a predictive technology to support virtual design and evaluation of underwater vehicles systems, employing a Computational Fluid Dynamics (CFD) based methodology for predicting stability and control derivatives. Computational Fluid Dynamics technology coupled with modeling and control system design will allow vehicle conceptual designs to be evaluated within the context of a realistic mission. The preliminary goal of this effort is to estimate stability and control derivatives of underwater vehicles from CFD data as an evaluation of the potential for this method to replace/reduce expensive experimental (i.e. tow-tank) tests. The need to establish a predictive capability technologies to support virtual design and evaluation of underwater vehicles systems, presented an opportunity to apply a multiblock, structured-grid, incompressible Navier-Stoke flow solver referred to as Tenasi, which have evolved over many years. The solver utilizes a state-of-the-art implicit upwind numerical scheme to solve the time-dependent Navier-Stokes equations in a generalized time-dependent curvilinear coordinate system. The numerical studies were performed for two underwater configurations to validate the accuracy and reliability of the present software tool. The computed results show favorable agreement with experimental data. The results from this study are very encouraging and strongly suggest that further development and application of this tool to more complicated underwater and high-speed supercavitating vehicles is needed. The results of this tool can be used to improve the performance of autonomous underwater vehicles. Methodologies and software tools are developed here that utilize vehicle-maneuvering simulated results to directly estimate standard hydrodynamic model coefficients, which are used for high-fidelity simulations and control system design.

Numerical Simulation of Reacting and Non-Reacting Nozzle Flows

The purpose of this paper is to present the results of several numerical studies of internal nozzle flows. The simulated flow fields are of non-reacting, ideal-gas flows, as well as flows with chemical reactions of the combustion products passing through the nozzle. The combustion process itself is not being simulated. The simulations are conducted using a number of flow solvers contained within the in-house suite of flow solvers collectively referred to as Tenasi. The older variants of these flow solvers are serial, structured-grid codes which allow for multiple sub-domain decomposition with arbitrary block-to-block connectivity. The newer code is a parallel, unstructured-grid solver that has been in a state of continual, and ongoing, development over the past seven years; sub-domain decomposition for this solver is completely arbitrary. Although there is noticeable difference in the code structure of the older and newer versions, the basic numerical algorithms are the same. Results from both the old and new solvers are compared to each other and to experiment for the non-reacting case. For a hypothetical reacting flow case, results from both the old and new solvers are compared to each other and to the results from the rocket engine analysis code, TDK, which is widely used throughout the industry. Comparison of these results to experiment (non-reacting) and TDK results (reacting) serves the purpose of validating the Tenasi solvers for nozzle flow applications.