Rapidly sheared homogeneous MHD turbulence in a rotating frame

7th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2011 Volume 2011-July, 2011© 2011 International Symposium on Turbulence and Shear Flow Phenomena, TSFP07. All rights reserved. Rapid distortion theory is applied to magneto-hydrodynamic turbulence that is sheared in a rotating frame. We describe analytically the modification of the three-dimensional velocity spectra due to the presence of an external magnetic field, using the quasi-static approximation. Using this analytical solution, we investigate the effect of the frame rotation in the evolution of one-point statistics, under the linear theory. For initial fields that are two-dimensional (but three-componential), with the axis of independence aligned with the flow direction, we derive analytically one-point statistics, such as the Reynolds stresses and the structure dimensionality tensor in physical space. The analytical results are compared with the linear three-dimensional exact numerical solution for initially isotropic homogeneous turbulence, and they show remarkable agreement. They describe accurately the tendencies in the morphology of the turbulent structures that develop as a result of the two competitive mechanisms of the frame rotation and the Joule dissipation. These results are in qualitative agreement with existing non-linear DNS results

Targeting inhaled aerosol delivery to upper airways in children: Insight from computational fluid dynamics (CFD).

Despite the prevalence of inhalation therapy in the treatment of pediatric respiratory disorders, most prominently asthma, the fraction of inhaled drugs reaching the lungs for maximal efficacy remains adversely low. By and large drug delivery devices and their inhalation guidelines are typically derived from adult studies with child dosages adapted according to body weight. While it has long been recognized that physiological (e.g. airway sizes, breathing maneuvers) and physical transport (e.g. aerosol dynamics) characteristics are critical in governing deposition outcomes, such knowledge has yet to be extensively adapted to younger populations. Motivated by such shortcomings, the present work leverages in a first step in silico computational fluid dynamics (CFD) to explore opportunities for augmenting aerosol deposition in children based on respiratory physiological and physical transport determinants. Using an idealized, anatomically-faithful upper airway geometry, airflow and aerosol motion are simulated as a function of age, spanning a five year old to an adult. Breathing conditions mimic realistic age-specific inhalation maneuvers representative of Dry Powder Inhalers (DPI) and nebulizer inhalation. Our findings point to the existence of a single dimensionless curve governing deposition in the conductive airways via the dimensionless Stokes number (Stk). Most significantly, we uncover the existence of a distinct deposition peak irrespective of age. For the DPI simulations, this peak (∼ 80%) occurs at Stk ≈ 0.06 whereas for nebulizer simulations, the corresponding peak (∼ 45%) occurs in the range of Stk between 0.03-0.04. Such dimensionless findings hence translate to an optimal window of micron-sized aerosols that evolves with age and varies with inhalation device. The existence of such deposition optima advocates revisiting design guidelines for optimizing deposition outcomes in pediatric inhalation therapy

Modeling the structure functions in linearly forced isotropic turbulence

7th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2011,Volume 2011-July, 2011© 2011 International Symposium on Turbulence and Shear Flow Phenomena, TSFP07. All rights reserved. The physics of the linear forcing of isotropic turbulence, allows for some useful estimates of the characteristic length scales of the turbulence produced during the statistically stationary phase. With such estimates we could practically define uniquely the stationary statistics by means of the boxsize of the simulation, the linear forcing parameter and the viscosity of each case. We use such estimations in the Karman-Howarth equation and we solve it in terms of the second and third order structure functions using a generalized Oberlack-Peters closure scheme. The resulting forms and the respective spectra are in very good agreement with experimental and DNS data

Using Coarrays to Parallelize Legacy Fortran Applications: Strategy and Case Study

This paper summarizes a strategy for parallelizing a legacy Fortran 77 program using the object-oriented (OO) and coarray features that entered Fortran in the 2003 and 2008 standards, respectively. OO programming (OOP) facilitates the construction of an extensible suite of model-verification and performance tests that drive the development. Coarray parallel programming facilitates a rapid evolution from a serial application to a parallel application capable of running on multicore processors and many-core accelerators in shared and distributed memory. We delineate 17 code modernization steps used to refactor and parallelize the program and study the resulting performance. Our initial studies were done using the Intel Fortran compiler on a 32-core shared memory server. Scaling behavior was very poor, and profile analysis using TAU showed that the bottleneck in the performance was due to our implementation of a collective, sequential summation procedure. We were able to improve the scalability and achieve nearly linear speedup by replacing the sequential summation with a parallel, binary tree algorithm. We also tested the Cray compiler, which provides its own collective summation procedure. Intel provides no collective reductions. With Cray, the program shows linear speedup even in distributed-memory execution. We anticipate similar results with other compilers once they support the new collective procedures proposed for Fortran 2015

Response of a Swirled Non-Premixed Burner to Fuel Flow Rate Modulation

Combustion instability studies require the identification of the combustion chamber response. In non-premixed devices, the combustion processes are influenced by oscillations of the air flow rate but may also be sensitive to fluctuations of the fuel flow rate entering the chamber. This paper describes a numerical study of the mechanisms controlling the response of a swirled non-premixed combustor burning natural gas and air. The flow is first characterized without combustion and LDV results are compared to Large Eddy Simulation (LES) data. The non-pulsated reacting regime is then studied and characterized in terms of fields of heat release and equivalence ratio. Finally the combustor fuel flow rate is pulsated at several amplitudes and the response of the chamber is analyzed using phase-locked averaging and first order acoustic analysis