A Low-Memory Block-Implicit Solver for Coupled Solution of the Species Conservation Equations on an Unstructured Mesh

2007 ◽  
Author(s):  
Ankan Kumar ◽  
Sandip Mazumder
Keyword(s):  
Unstructured Mesh ◽  
Gaussian Elimination ◽  
Species Conservation ◽  
Iterative Solution ◽  
Maximum Efficiency ◽  
Efficiency Gain ◽  
Conservation Equations ◽  
Aspect Ratios ◽  
Coupled Solution ◽  
Number Of Cells

Many reacting flow applications mandate coupled solution of the species conservation equations. A low-memory coupled solver was developed to solve the species transport equations on an unstructured mesh. The first step was the decomposition of the domain into sub-domains comprised of geometrically contiguous cells—a process termed internal domain decomposition (IDD). This was done using the binary spatial partitioning (BSP) algorithm. Following this step, for each subdomain, the discretized equations were set up, written in block implicit form, and solved using two different solvers: a direct solver using Gaussian elimination and an iterative solver based on Krylov sub-space iterations, i.e., the Generalized Minimum Residual (GMRES) solver. Overall (outer) iterations were then performed to treat explicitness at sub-domain boundaries and non-linearities in the governing equations. The solver is demonstrated for a simple two-dimensional multi-component diffusion problem involving 5 species. Sample calculations show that the solver with direct solution for each block is most efficient if the number of cells in each block is small—typically tens of cells, while the solver with iterative solution for each block is most efficient if the number of cells is relatively large—typically hundreds of cells. Overall the iterative solution based solver performed best, with maximum efficiency gain of a factor of seven over a block Gauss-Seidel (GS) solver and was found to be comparable or better in efficiency than a block-implicit Alternating Direction Implicit (ADI) solver. The gain in efficiency was found to increase with increase in cell aspect ratios.

An Unstructured Reacting Flow Solver With Coupled Implicit Solution of the Species Conservation Equations

2008 ◽  
Author(s):  
Ankan Kumar ◽  
Sandip Mazumder
Keyword(s):  
Species Conservation ◽  
Domain Size ◽  
Reacting Flow ◽  
Computational Domain ◽  
Conservation Equations ◽  
Flow Solver ◽  
As Species ◽  
Minimum Residual ◽  
Volume Method ◽  
Coupled Solution

Many reacting flow applications mandate coupled solution of the species conservation equations. A low-memory coupled solver was developed to solve the species transport equations on an unstructured mesh with implicit spatial as well as species-to-species coupling. First, the computational domain was decomposed into sub-domains comprised of geometrically contiguous cells—a process termed internal domain decomposition (IDD). This was done using the binary spatial partitioning (BSP) algorithm. Following this step, for each sub-domain, the discretized equations were developed using the finite-volume method, written in block implicit form, and solved using an iterative solver based on Krylov sub-space iterations, i.e., the Generalized Minimum Residual (GMRES) solver. Overall (outer) iterations were then performed to treat explicitness at sub-domain interfaces and non-linearities in the governing equations. The solver is demonstrated for a laminar ethane-air flame calculation with five species and a single reaction step, and for a catalytic methane-air combustion case with 19 species and 22 reaction steps. It was found that the best performance is manifested for sub-domain size of about 1000 cells, the exact number depending on the problem at hand. The overall gain in computational efficiency was found to be a factor of 2–5 over the block Gauss-Seidel procedure.

41 EFFICIENT STRATEGY FOR INTERSPECIFIC CLONING IN FELIDS

2014 ◽  
Vol 26 (1) ◽  
pp. 134
Author(s):  
L. N. Moro ◽  
M. I. Hiriart ◽  
J. Jarazo ◽  
C. Buemo ◽  
A. Sestelo ◽  
...  
Keyword(s):  
Species Conservation ◽  
Total Cell ◽  
Domestic Cat ◽  
Control Group ◽  
Felis Silvestris ◽  
Blastocyst Formation ◽  
Acinonyx Jubatus ◽  
Cell Numbers ◽  
Number Of Cells

Most of the 36 species of wild felids are at a level of threat, and interspecific SCNT (iSCNT) comes as a strategy to contribute to these species conservation. The aim of this study was to evaluate the effect of embryo aggregation in cheetah (Ch, Acinonyx jubatus), bengal (Ben, a hybrid between Felis silvestris and Prionailurus bengalensis), and domestic cat (DC, Felis silvestris) embryos generated by cloning. DC oocytes were in vitro matured and zona-free SCNT (with DC fibroblasts) or iSCNT (with Ch or Ben fibroblasts) was performed. The reconstructed embryos were activated with 5 μM ionomycin and 1.9 mM 6-DMAP, and cultured in SOF using microwells. Cloned embryos were cultured individually or as 2-embryo aggregates. The experimental groups were Ch1X, Ch2X, Ben1X, Ben2X, and the control groups were DC1X and DC2X. Embryo development was compared by Fisher's exact test (P ≤ 0.05). Embryo aggregation improved cleavage (Day 2) and blastocyst (Day 7) rates per well in all the groups (87.2% v. 96.7%, 83.8% v. 93.3% and 87.6% v. 98.2% for cleavage; and 13.7% v. 28.6%, 33.3% v. 43.8% and 27.4% v. 47.7% for blastocyst, for Ch1X (n = 102), Ch2X (n = 91), Ben1X (n = 154), Ben2X (n = 105), DC1X (n = 113), and DC2X (n = 109), respectively. Moreover, the Ch2X blastocyst rate was statistically similar as the control group DC1X. The mean total cell numbers of the blastocysts obtained were 264 ± 211 and 400.8 ± 97 for Ch1X and Ch2X, 278 ± 62 and 517 ± 104 for Ben1X and Ben2X, 385 ± 127 and 625 ± 183 for DC1X and DC2X, respectively. Although no statistical differences were obtained between the 1X and 2X groups, the 2X groups nearly doubled the average number of cells compared with the 1X groups. Blastocysts were also classified as grade 1 (expanded blastocysts with a well-defined ICM), grade 2 (expanded blastocysts without a well-defined ICM), and grade 3 (not expanded blastocysts). This classification showed an increase in grade 1 DC2X blastocyst compared with DC1X blastocysts (36.7% v. 16.1%), but no differences were observed in the other species. Expression of OCT-4 was assessed by inmunocytochemistry. The cheetah blastocysts markedly over-expressed this protein: the percentage of cells that expressed OCT-4 in Ch1X, Ch2X, Ben1X, Ben2X, DC1X, and DC2X was 88.2, 80.2, 46.3, 45.4, 51, and 47.4%, respectively, with statistical differences among all the groups except Ben1X and Ben2X. The proportion of OCT-4 expressing cells over total cell numbers was analysed by the difference of proportions test (P ≤ 0.05). In conclusion, iSCNT resulted in high rates of blastocyst formation, especially when embryo aggregation was applied. This strategy has not been previously evaluated in felids or iSCNT procedures, and has been demonstrated to improve blastocyst formation, the number of cells in the 3 groups, and the blastocyst quality in the DC. Other pluripotent genes besides OCT-4 should be studied to determine whether the overexpression of this gene in cheetah embryos is the consequence of an inefficient nuclear reprogramming that prevents a correct regulation. Finally, the iSCNT and embryo aggregation could contribute to species conservation in felids.

scholarly journals Numerical–Experimental Performance Assessment of a Non-Concentrating Solar Thermoelectric Generator (STEG) Operating in the Southern Hemisphere

Energies ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2666 ◽  
Author(s):  
Nelson Calderón-Henao ◽  
Osvaldo José Venturini ◽  
Emerson Henrique Medina Franco ◽  
Electo Eduardo Silva Lora ◽  
Helton Fernando Scherer ◽  
...  
Keyword(s):  
Solid State ◽  
Southern Hemisphere ◽  
Photovoltaic Cells ◽  
Operating Conditions ◽  
Maximum Efficiency ◽  
Thermoelectric Device ◽  
Efficiency Gain ◽  
Efficiency Increase ◽  
Solar Thermoelectric Generator ◽  
Time Of Year

This study assesses the performance of a solid-state semiconductor-based hybrid photovoltaic-thermoelectric device that aims to harness both solar irradiance and heat dissipated from photovoltaic cells operating in Foz do Iguaçu city. Initially, the technologies involved, and the arrangement of the proposed device are presented; the modeling process of the generator operation under local operating conditions and taking into account solar energy availability is described later. The thermal energy harvesting brings out an average annual efficiency gain of 4.42% and a maximum efficiency increase of 6.05% (in the fall equinox) compared to standalone PV cell operation. The power output increase due to the utilization of the heat dissipated by the PV cells was substantial, reaching values ranging from 14.82% to 40.54%, depending on the time of year. The novelty of this research stems from the field power generation forecast, in southern hemisphere, for a new STEG device that combines photovoltaic cells and solid-state thermoelectric modules.

A New Practical Approach to the Design of Industrial Axial Fans: Part II — Forward-Swept Blades With Low Hub-to-Tip Ratio

2019 ◽  
Author(s):  
Massimo Masi ◽  
Andrea Lazzaretto
Keyword(s):  
Design Method ◽  
Pressure Coefficient ◽  
Rate Coefficients ◽  
Maximum Efficiency ◽  
Stable Operation ◽  
Pressure Curve ◽  
Simple Method ◽  
Aspect Ratios ◽  
Wide Range ◽  
Axial Fans

Abstract The authors previously suggested a simple method to design forward-swept axial-flow rotors with blades having low hub-to-tip and high aspect ratios. This design method was demonstrated experimentally to increase the aeraulic performance of a small tube-axial fan having unswept blades and 0.4 hub-to-tip ratio, while maintaining the efficiency in the entire operation range. However, the method has not yet been assessed by experimental tests of lower hub-to-tip ratio designs where the strong three-dimensionality of the actual blade passage flow could compromise its validity. This assessment is the object of the present paper, which is aimed at examining the practical effectiveness of the forward-swept blade design method for low hub-to-tip ratio tube-axial fans. To this end, past results of the authors’ work are supported here by the design of a new 315mm forward-swept industrial fan derived from the 0.28 hub-to-tip ratio design presented in Part I of this paper. The ISO-5801 aerodynamic performance tests at blade Reynolds number of approximately 60,000 show that the method permits the design of forward-swept industrial fans capable of pressure coefficients in excess of 0.02 at aeraulic efficiency well above 60%, in a wide range of flow rate coefficients and blade positioning angles. Moreover, the method allows obtaining a pressure coefficient equal to 0.021 at 70% maximum efficiency, with an improvement of both the stall margin and stable operation pressure curve of the unswept design, if applied in combination with the complete fan design method presented in Part I of this paper.

Effects of Vibrational Relaxation on Weak Shock Wave Structure in Air

2011 ◽  
Author(s):  
Takeharu Sakai ◽  
Yoshikazu Makino ◽  
Yusuke Naka ◽  
Akira Murakami
Keyword(s):  
Shock Wave ◽  
Vibrational Relaxation ◽  
Fluid Dynamic ◽  
Species Conservation ◽  
Weak Shock ◽  
Wave Structure ◽  
Weak Shock Wave ◽  
Conservation Equations ◽  
Wide Range ◽  
Energy Equations

A computational fluid dynamic method is developed to calculate the long range propagation of weak shock wave with the vibrational relaxation in air. Vibrational relaxation kinetics among N2, O2, and H2O is accounted for by solving each species conservation equations with total mass, momentum and energy equations. The conservation equations are solved using a moving grid technique to capture the distortion of the wave during propagation. The propagation of the wave with an overpressure value typically observed in sonic boom on the ground is analyzed using the developed method. The computed results are mainly presented to show the ability to capture a dispersed nature in waves under different humidity conditions due to vibrational relaxation. The present result shows that the variation of a converged wave thickness dependent on a wide range of humidity can be recognized clearly by using the present method.

scholarly journals Numerical Investigation of the Performance Impact of Stator Tilting Endwall Designs on a Mixed Flow Turbine

2021 ◽  
Vol 6 (2) ◽  
pp. 14
Author(s):  
Yang Gao ◽  
Jens Fridh ◽  
Richard Morrison ◽  
Pangbo Ren ◽  
Stephen Spence
Keyword(s):  
Optimal Design ◽  
Velocity Ratio ◽  
Maximum Efficiency ◽  
Efficiency Gain ◽  
Efficiency Curve ◽  
Peak Efficiency ◽  
Low Velocity ◽  
Mixed Flow ◽  
Baseline Design ◽  
Numerical Predictions

This paper numerically investigates stator endwall designs for a mixed flow turbine. One key design parameter studied is the tilting angle of the stator endwall. By examining stator designs with different tilting angles, the aim of this paper is to improve the efficiency of the studied mixed flow turbine at low velocity ratio working conditions. The performance curve at the design speed was chosen for the comparison between the baseline design and the tilted endwall designs. First, the numerical predictions for the baseline design were validated with experimental data. Then, to understand the mechanism of the performance variation between the different designs, the internal flow field was analyzed in detail. It was found that the tilting stator endwall could form a geometric “kink” in the endwall profiles. On the shroud side, certain designs with such kink caused local flow separations upstream the rotor leading edge. This separation could have the effect of reducing the intensity of the tip leakage vortex and the exit kinetic energy losses at the rotor outlet and may also improve the performance of the exhaust diffuser. As a result, the peak of the efficiency curve shifted toward lower velocity ratio. If the turbine stage incorporated a downstream exhaust diffuser, the optimal design in this study showed a shift of the velocity ratio of the peak efficiency point from 0.62 to 0.60 compared with the baseline. The maximum efficiency improvement was 1.3% points, which occurred at low velocity ratio. Meanwhile, the peak efficiency was 0.2% points higher than the baseline. If the exhaust diffuser was removed, a similar shift of the efficiency curve was observed but less efficiency gain was achieved at the low velocity ratio condition. A preliminary unsteady simulation was also conducted for the optimal design in this study.

Experimental Study on the Performance and Pressure Fluctuations of a Regenerative Gas Blower for Different Design Parameters

2011 ◽  
Author(s):  
Younghoon Kim ◽  
Shin Hyoung Kang ◽  
Yonggyu Noh
Keyword(s):  
Pressure Fluctuation ◽  
Pressure Fluctuations ◽  
Fast Response ◽  
Fuel Cell Vehicle ◽  
Maximum Efficiency ◽  
Design Parameters ◽  
Pressure Transducers ◽  
Total Enthalpy ◽  
Aspect Ratios ◽  
Blade Thickness

A regenerative gas blower design for fuel cell vehicle is presented. Two issues studied concern non-dimensional performance characteristics under various design parameters and the noise of the blower due to unsteady pressure fluctuation. Non-dimensional performance curves were measured at various rotating speeds and gas mixture ratios. Blower models using different design parameters such as the stripper angle, blade aspect ratios and blade thickness ratios were tested. The effects that aforementioned parameters had on performance were investigated. Surface pressure fluctuations were measured in the channel close to both ends of the stripper using fast-response pressure transducers. A sharp blade increases the maximum isentropic total enthalpy coefficient and the maximum efficiency because the pressure loss coefficient of the circulatory flow is reduced. A small stripper angle enhanced the maximum isentropic total enthalpy coefficient and the maximum efficiency because working sections was lengthened. The enlarged stripper angle and the low pressure difference across the stripper reduce the magnitude of pressure fluctuation at the blade passing frequency.

On a New Passive Scalar Equation With Variable Mass Diffusivity: Flow Between Parallel Plates

2010 ◽  
Vol 132 (11) ◽  
Author(s):  
Fabio Gori ◽  
Andrea Boghi
Keyword(s):  
Variable Mass ◽  
Species Conservation ◽  
Mass Conservation ◽  
Passive Scalar ◽  
Conservation Equation ◽  
Average Concentration ◽  
Parallel Plates ◽  
Conservation Equations ◽  
Concentration Variance ◽  
Mass Diffusivity

The present work investigates mass conservation equations in turbulent flow between parallel plates with variable mass diffusivity. Species conservation equations are relative to the average concentration, as well as to the concentration variance. The product of fluctuating mass diffusivity and space gradient of concentration fluctuation is appearing in the equation of mean and concentration variance. A physical interpretation is given to the different terms. The assumption of a relation between mass diffusivity and concentration allows writing expressions for average and fluctuating mass diffusivity, which can be simplified on the basis of theoretical considerations. The new mass flux is expressed as a function of mass diffusivity and a gradient of concentration variance. Further considerations make it possible to model the new terms appearing in the concentration variance equation. The mass conservation equation can be solved when coupled to the equation of concentration variance. The equations are solved numerically for flow between parallel plates in order to evaluate the influence of the new terms.

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