173 research outputs found
EFFECT OF CHEMICAL NON-EQUILIBRIUM ON FLOW PARAMETERS IN THE INTERMEDIATE HYPERSONIC REGIME
The new solver hypersonicIithFoam has been developed in
the OpenFOAM framework. OpenFOAM has rhoCentralFoam
which is a density based N-S solver, is used as a base solver.
Additional features are incorporated to model reacting flows,
variable multi-species diffusion and thermodynamic proper-
ties of high-temperature air. The solver is implemented to
model the transport properties based on a kinetic theory for its
widespread applicability. Viscosity and Thermal conductivity are
obtained using the model based on Lennard-Jones potential, and
Chapman-Enskog diffusivity model is used to compute binary dif-
fusion coefficient. Multicomponent mixture properties are calcu-
lated based on a mole fraction. All species are assumed to be in
thermodynamic equilibrium, so the state of the gas is governed
by single equilibrium temperature. The solver is tested with the
available experimental data for Heat flux and coefficient of pres-
sure Cp distribution over a surface of ELECTRE article. The hy-
personic solver is shown significant improvement over a conven-
tional compressible solver. Simulations are carried out for the
flow over a sphere at different altitudes using both the conven-
tional and the hypersonic solver for qualitative and quantitative
comparisons. Post shock temperature and peak heat flux values
are remarkably reduces due to the implementation of real gas ef-
fects and air chemistry. Rarefaction effects become significant
from 70 km
Computational Analysis of Side Jet Interaction With a Super-sonic Cross-flow
We have numerically investigated the interaction of a side jet
positioned on the small rocket, with the supersonic cross-flow.
An open source CFD tool, OpenFOAM is used to model the
complex flow of a jet-atmosphere interaction. The flow fields
are computed by the steady 3-dimensional Navier-Stokes solver
with k- ! SST turbulence model. Our solver is validated with
the experimental pressure data available on the rocket wall and
a systematic study is done by varying parameters like jet pressure
ratio. Aerothermodynamic coefficients for various flow
conditions are reported, and pitching moments and normal
forces are found to vary linearly with the jet pressure ratios.
Possible contamination of the on-board sensor located on the
rocket wall due to impinging plumes is also examined. This
study helps in designing effective missile control by selection
of the location of jet and pressure ratios
Aero-Thermodynamics Optimization of Re-Entry Capsule in the Slip Flow Regime
We carry out numerical simulations to optimize the re-
entry capsule configurations based on aero-thermodynamic
properties such as drag, pressure and heat load. The open
source software OpenFOAM is used with the compress-
ible computational fluid dynamics (CFD) solver rhoCen-
tralFoam. CFD solver is implemented with the first-order
Maxwell’s velocity slip and the Smoluchowski temperature
jump boundary conditions. We report results for different
altitudes and Mach numbers with varying second cone an-
gle and bluntness of the re-entry capsule. It is noted that the
heat loads are greatly reduced by changing the capsule con-
figuration from single to bi-cone. With increasing second
cone angle heat loads are enhanced, but the average drag
and pressure coefficients found to be least sensitive. How-
ever, with increase in bluntness the average value of heat
load decrease slightly and the peak value significantly, while
drag values exhibit contrasting behaviour
Numerical Analysis of Rarefied Hypersonic and Chemically Reacting Flow-field
We have developed an open source CFD tool, which can
simulate high temperature and chemically reacting flow-field
in the rarefied regime. It is used to carry out simulations in the
intermediate hypersonic flow regime (Mach number range from
8 to 15). Solver is tested with available data for high speed and
rarefied flow applications. Heat load values for blunt conical
surface and shock standoff distance for sphere are obtained
with our solver and good agreement has been exhibited with
the experimental data
Effect of Nozzle Divergence Angle on Plume Expansion In Outer-Space Conditions
We carry out numerical simulations to investigate
the effect of nozzle divergence angle on back flow of
plume expansion into rarefied atmosphere.
Results are
obtained using open source compressible computational
fluid dynamics (CFD) solver.
Non-equilibrium slip and
jump boundary conditions for velocity and temperature are
implemented to capture rarefaction rarefaction effects in
the slip flow regime. The solver has been validated with
the experimental data for a nozzle flow in the slip flow
regime. We explore the non-linear non-equilibrium gas flow
physics of a supersonic jet expansion. We report results of
pressure, heat and drag coefficients for different divergent
angles (
12
0
,
15
0
and
20
0
) at 80 km altitude conditions. The
slip based results for heat loads significantly under-predict
the no-slip ones, while for pressure and drag coefficients,
deviations are found to be minute. It is noticed that thrust
coefficient of nozzle increases with increase in divergence
angle, however, nozzle with divergent angle of
15
0
led to
minimum drag and heat transfer load on the critical region.
The current study is important from the perspective of the
overall aero-thermodynamic design of a typical supersonic rocket model operating under rarefied conditions
A nearest level control technique for an asymmetric source configuration of multi-level inverter topology
In this paper, an asymmetric source configuration of Multilevel Inverter (MLI) topology has been proposed. It consists of eight unidirectional switches, two bidirectional switches and four isolated DC sources. By considering 1:5 and 1:4 source configurations, the inverter produces 25-level and 21-level outputs respectively with the same switching action. For producing negative voltage levels, there is no requirement of separate backend H-bridge and inherently produces both positive and negative voltage levels. The main advantage of this topology is that in every state, only four switches are in ON mode and else are in OFF state. It also gives less per unit Total Standing Voltage (TSV) and thereby cost requirement of semiconductor devices can become decreases. For generating gate pulses, the simple Nearest Level Control (NLC) has been used by considering the round function. This technique is basically a fundamental switching frequency technique thereby switching losses are greatly reduces as compared with high switching frequency Pulse Width Modulation (PWM) techniques and it is particularly suitable for large number of levels. With this control technique, there is no inrush current has been developed at the input of DC sources. Finally, with step change in Modulation Index (MI) values the proposed topology with two different source configurations have been validated through MATLAB/Simulink platform
Modeling of Knudsen Layer Effects in the Micro-Scale Backward-Facing Step in the Slip Flow Regime
The effect of the Knudsen layer in the thermal micro-scale gas flows has been investigated.
The effective mean free path model has been implemented in the open source computational
fluid dynamics (CFD) code, to extend its applicability up to slip and early transition flow regime.
The conventional Navier-Stokes constitutive relations and the first-order non-equilibrium boundary
conditions are modified based on the effective mean free path, which depends on the distance from
the solid surface. The predictive capability of the standard ‘Maxwell velocity slip—Smoluchwoski
temperature jump’ and hybrid boundary conditions ‘Langmuir Maxwell velocity slip—Langmuir
Smoluchwoski temperature jump’ in conjunction with the Knudsen layer formulation has been
evaluated in the present work. Simulations are carried out over a nano-/micro-scale backward facing
step geometry in which flow experiences adverse pressure gradient, separation and re-attachment.
Results are validated against the direct simulation Monte Carlo (DSMC) data, and have shown
significant improvement over the existing CFD solvers. Non-equilibrium effects on the velocity
and temperature of gas on the surface of the backward facing step channel are studied by varying
the flow Knudsen number, inlet flow temperature, and wall temperature. Results show that the
modified solver with hybrid Langmuir based boundary conditions gives the best predictions when
the Knudsen layer is incorporated, and the standard Maxwell-Smoluchowski can accurately capture
momentum and the thermal Knudsen layer when the temperature of the wall is higher than the
fluid flow
Integrated Analysis of Clinical and Microbiome Risk Factors Associated with the Development of Oral Candidiasis during Cancer Chemotherapy.
Oral candidiasis is a common side effect of cancer chemotherapy. To better understand predisposing factors, we followed forty-five subjects who received 5-fluorouracil- or doxorubicin-based treatment, during one chemotherapy cycle. Subjects were evaluated at baseline, prior to the first infusion, and at three additional visits within a two-week window. We assessed the demographic, medical and oral health parameters, neutrophil surveillance, and characterized the salivary bacteriome and mycobiome communities through amplicon high throughput sequencing. Twenty percent of all subjects developed oral candidiasis. Using multivariate statistics, we identified smoking, amount of dental plaque, low bacteriome and mycobiome alpha-diversity, and the proportions of specific bacterial and fungal taxa as baseline predictors of oral candidiasis development during the treatment cycle. All subjects who developed oral candidiasis had baseline microbiome communities dominated by Candida and enriched in aciduric bacteria. Longitudinally, oral candidiasis was associated with a decrease in salivary flow prior to lesion development, and occurred simultaneously or before oral mucositis. Candidiasis was also longitudinally associated with a decrease in peripheral neutrophils but increased the neutrophil killing capacity of Candida albicans. Oral candidiasis was not found to be associated with mycobiome structure shifts during the cycle but was the result of an increase in Candida load, with C. albicans and Candida dubliniensis being the most abundant species comprising the salivary mycobiome of the affected subjects. In conclusion, we identified a set of clinical and microbiome baseline factors associated with susceptibility to oral candidiasis, which might be useful tools in identifying at risk individuals, prior to chemotherapy
Chemotherapy-induced oral mucositis is associated with detrimental bacterial dysbiosis.
BACKGROUND: Gastrointestinal mucosal injury (mucositis), commonly affecting the oral cavity, is a clinically significant yet incompletely understood complication of cancer chemotherapy. Although antineoplastic cytotoxicity constitutes the primary injury trigger, the interaction of oral microbial commensals with mucosal tissues could modify the response. It is not clear, however, whether chemotherapy and its associated treatments affect oral microbial communities disrupting the homeostatic balance between resident microorganisms and the adjacent mucosa and if such alterations are associated with mucositis. To gain knowledge on the pathophysiology of oral mucositis, 49 subjects receiving 5-fluorouracil (5-FU) or doxorubicin-based chemotherapy were evaluated longitudinally during one cycle, assessing clinical outcomes, bacterial and fungal oral microbiome changes, and epithelial transcriptome responses. As a control for microbiome stability, 30 non-cancer subjects were longitudinally assessed. Through complementary in vitro assays, we also evaluated the antibacterial potential of 5-FU on oral microorganisms and the interaction of commensals with oral epithelial tissues.
RESULTS: Oral mucositis severity was associated with 5-FU, increased salivary flow, and higher oral granulocyte counts. The oral bacteriome was disrupted during chemotherapy and while antibiotic and acid inhibitor intake contributed to these changes, bacteriome disruptions were also correlated with antineoplastics and independently and strongly associated with oral mucositis severity. Mucositis-associated bacteriome shifts included depletion of common health-associated commensals from the genera Streptococcus, Actinomyces, Gemella, Granulicatella, and Veillonella and enrichment of Gram-negative bacteria such as Fusobacterium nucleatum and Prevotella oris. Shifts could not be explained by a direct antibacterial effect of 5-FU, but rather resembled the inflammation-associated dysbiotic shifts seen in other oral conditions. Epithelial transcriptional responses during chemotherapy included upregulation of genes involved in innate immunity and apoptosis. Using a multilayer epithelial construct, we show mucositis-associated dysbiotic shifts may contribute to aggravate mucosal damage since the mucositis-depleted Streptococcus salivarius was tolerated as a commensal, while the mucositis-enriched F. nucleatum displayed pro-inflammatory and pro-apoptotic capacity.
CONCLUSIONS: Altogether, our work reveals that chemotherapy-induced oral mucositis is associated with bacterial dysbiosis and demonstrates the potential for dysbiotic shifts to aggravate antineoplastic-induced epithelial injury. These findings suggest that control of oral bacterial dysbiosis could represent a novel preventive approach to ameliorate oral mucositis
C. albicans Colonization of Human Mucosal Surfaces
Background: Candida albicans is a low level commensal organism in normal human populations with the continuous potential to expand and cause a spectrum of clinical conditions. Methodology/Principal Findings: Using ex vivo human organ cultures and populations of primary human cells, we have developed several related experimental systems to examine early-stage interactions between C. albicans and mucosal surfaces. Experiments have been conducted both with exogenously added C. albicans and with overtly normal human mucosal surfaces supporting pre-existing infections with natural isolates of Candida. Under different culture conditions, we have demonstrated the formation of C. albicans colonies on human target cells and filament formation, equivalent to tissue invasion. Conclusions/Significance: These organ culture systems provide a valuable new resource to examine the molecular and cellular basis for Candida colonization of human mucosal surfaces
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