Numerical lnvestigation of Disturbance Environments in Low Pressure Turbines

Using a series of direct numerical simulations, the individual and cumulative effects of various disturbance environments existing in a low pressure turbine (LPT) are investigated. In particular, the effects of free-stream turbulence (FST), unsteady wakes, roughness and blade oscillations on the separation-induced transition on the suction surface of a low pressure turbine blade are analyzed. Two configurations are considered: (i) a flat plate subjected to streamwise pressure gradient representative of the suction surface of a low pressure turbine blade, (ii) a flat plate subjected to a convecting free-stream vortex of fixed strength and at a fixed height over the plate. The first configuration represents the ‘ultra high-lift’ blades for the next generation low pressure turbine. The local pressure gradient induced by the convecting vortex in the second configuration is representative of the adverse pressure gradient on the suction surface of a low pressure turbine blade. The results are validated against existing experimental or numerical data and it is demonstrated that the numerical framework has captured most of the phenomena to a reasonable level of accuracy. A kernel experiment for bypass transition is simulated for the vortex-induced instability. The effect of the convection speed and strength of the vortex are discussed and the paths of transition adopted are distinguished. At low disturbance levels, the transition to turbulence is primarily due to the breakdown of ‘Kelvin-Helmholtz’ roll up vortices. In the presence of aeroelastic blade oscillations, unsteady wakes, free-stream turbulence and roughness, transition takes the bypass route and the results show evidence of streamwise streaks. These streaks impart spanwise waviness to the separated shear layer and cause early destabilisation. The blade oscillation has an effect in reducing the separated region and hence, the profile loss, which is further accentuated in the presence of free-stream turbulence. A blade fluctuating at higher reduced frequency is found to be more effective in shrinking the separation region. Blade vibration is found to increase the level of pre-transitional fluctuations, without having a significant influence on the growth beyond separation. There is a cumulative effect in suppressing the separation region when blade oscillation and free-stream turbulence are studied in conjunction, although the additional effect of free-stream turbulence is marginal. A secondary separation bubble, noted in the unperturbed flow, is reduced in size with blade oscillation and further reduced in the presence of free-stream turbulence. The vortex-induced instability has been proposed to be a unit process of free-stream turbulence, the effect of which is studied in the presence of a discrete roughness element (similar in functionality to a trip wire). The roughness element triggers early transition by destabilizing the mean flow. Streaks are observed in the presence of the convecting and rotating cylinder, generating a vortex of fixed strength, and are enhanced by the presence of roughness in the pre-transitional zone. Enhanced spanwise waviness is noted with the roughness, leading to earlier breakdown to turbulence. The route of transition and the origin of three-dimensionality marked by the prominence of the vortex stretching is shown. An optimum range of convection speeds of the free-stream vortex is obtained and the maximum receptivity is noted at a speed of 0.386, which concurs with prior experiments on a periodic convecting vortex (Kendall, 1987). The unsteady wake has a direct effect on the velocity profile. A lag is noted between the wake passing and transition. While the wake convects at the local free-stream velocity, its impression in the boundary layer convects much slower, between 50% and 70% of the local free-stream velocity. Both unsteady wakes and blade oscillation promote near-wall mixing. The unsteady wakes and blade oscillations have a conjunctive effect on reducing the size of separation bubble. The secondary separation bubble observed in the unperturbed flow is reduced with the presence of wakes and is completely suppressed with the addition of the blade oscillation. Turbulent kinetic energy production increases with increasing perturbation levels, with the maximum effect seen for the combination of wakes and oscillation. A receptivity method based on disturbance enstrophy transport equation (DETE) is proposed. The disturbance enstrophy is evaluated as the difference between the instantaneous and mean enstrophies, and while these are positive definite quantities, the difference may not be so. This aspect of disturbance enstrophy has been used meaningfully to obtain new information about the flow instability, such as segmenting regions of flow instabilities into those dictated by positive growth rates of disturbance enstrophy, and those due to its negative counterpart. The positive growth rates are associated with large scale coherence in the free-stream whereas the negative growth rates are found to be arising in near-wall viscous structures (Sengupta et al., 2019a,b). The extension of this method to structure detection and comparison against existing vortex identification methods, indicates the ability of the DETE method to capture small-scale structures induced by the viscous term of the Navier- Stokes equation. DETE has been used for the two configurations operating with varying perturbation levels and valuable insight pertaining to the flow dynamics has been attained with respect to its budget terms. In particular, the role of vortex stretching in leading the flow to three-dimensionality is highlighted. The global and local spatio-temporal receptivity analysis of flows perturbed by plate oscillations, wakes and free-stream excitation yields a spatio-temporal wave front to be the causal mechanism for flow transition. This is essentially representative of the nonmodal part of the disturbance spectrum. While this flow instability has already been established for geophysical flows such as tsunami and other fluid dynamical problems such as for zero pressure gradient boundary layer formed over a semi-infinite flat plate excited from inside the shear layer, its role for pressure gradient dominated flows (such as in LPTs) is shown for the first time. The importance of nonlinearity and its dispersion effects is shown, specifically for flows excited at the free stream, even when the onset of disturbances follows a linear mechanism. The need for using a global, nonlinear, spatio-temporal setup is established in order to capture all pertinent flow physics.Cambridge India Ramanujan Scholarshi

Methyl esterification of fatty acids and eicosanoids with a novel reagent trimethylsilyldiazomethane for analysis by gas chromatography-mass spectrometry

Fatty acids are compounds with limited water solubility that belong to the lipid class of bio-organic compounds and can be utilized as a source of energy by the body or as precursors to oxidized compounds that have roles in inflammation and in the regulation of vascular tone. The prostaglandins are naturally occurring 20-carbon cyclopentano fatty acid derivatives produced in mammalian tissue from polyunsaturated fatty acids (PUFAs) and are generated from endoperoxide precursors of arachidonic acid and related polyunsaturated fatty acids by the enzyme cyclo-oxygenase (COX). The lipoxygenase (LOX) enzymes convert arachidonic acid into hydroperoxy derivatives of PUFAs termed leukotrienes, which play a role in asthma and allergies. The reagent trimethyl silyl diazomethane (TMSD) which is less toxic and explosive than other reagents such as diazomethane, has been developed for use in the methyl esterification of drugs such as penicillin and some fatty acids. The objectives of the research were to (1) optimize the TMSD reaction conditions, (2) determine whether the TMSD reaction could support methylation of prostaglandins and other oxidized products of arachidonic acid, such as prostaglandins PGE2 and PGF2α, (3) develop calibration curves for the fatty acids and prostaglandins with appropriate internal standards for use with GC-MS, and (4) determine whether this method could be used to characterize by GC-MS these lipids in cell culture and in other cell-free systems, such as those containing enzymes like COX

Acoustic Equation in a Lossy Medium

Here, the acoustic equation for a lossy medium is derived from the first principle from the linearized compressible Navier-Stokes equation without Stokes' hypothesis. The dispersion relation of the governing equation is obtained, which exhibits both the dispersive and dissipative nature of the acoustic perturbations traveling in a lossy medium, depending upon the length scale. We specifically provide a theoretical cut-off wave number above which the acoustic equation represents a diffusive nature. Such a behavior has not been reported before, as per the knowledge of the authors

Equation for Aeroacoustics in a Quiescent Environment

The perturbation equation for aeroacoustics has been derived in a dissipative medium from the linearized compressible Navier-Stokes equation without any assumption, by expressing the same in spectral plane as in Continuum perturbation field in quiescent ambience: Common foundation of flows and acoustics Sengupta et al., Phys. Fluids,35, 056111 (2023). The governing partial differential equation (PDE) for the free-field propagation of the disturbances in the spectral plane provides the dispersion relation between wavenumber and circular frequency in the dissipative medium, as characterized by a nondimensional diffusion number. Here, the implications of the dispersion relation of the perturbation field in the quiescent medium are probed for different orders of magnitude of the generalized kinematic viscosity, across large ranges of the wavenumber and the circular frequency. The adopted global spectral analysis helps not only classify the PDE into parabolic and hyperbolic types, but also explain the existence of a critical wavenumber depending on space-time scales.Comment: 19 pages, 10 figure

Perturbation Field in The Presence of Uniform Mean Flow: Doppler Effect for Flows and Acoustics

Having developed the perturbation equation for a dissipative quiescent medium for planar propagation using the linearized compressible Navier-Stokes equation without the Stokes' hypothesis \cite{arxiv2023}, here the same is extended where a uniform mean flow is present in the ambiance to explore the propagation properties for the Doppler effect.Comment: 15 pages, 6 figure

Spatial and Temporal Heterogeneity of Microbial Life in Artificial Landscapes

The Landscape Evolution Observatory (LEO) project at Biosphere 2 consists of three replicated artificial landscapes which are sealed within a climate-controlled glass house. LEO is composed of basaltic soil material with low organic matter, nutrients, and microbes. The landscapes are built to resemble zero-order basins and enables researchers to observe hydrological, biological, and geochemical evolution of landscapes in a controlled environment. This study is focused on capturing microbial community dynamics in LEO soil, pre- and post-controlled rainfall episodes. Soil samples were collected from six different positions and at five depths in each of the three slopes followed by DNA extraction from 180 samples and sent for sequencing. The average concentration of DNA recovered from each sample was higher in the post-rainfall samples than the pre-rainfall samples. This trend was seen throughout all three slopes. However, the variance in results among the individual samples between the three slopes indicates a variability between the slopes. The sequence data will be evaluated to reveal spatial and temporal heterogeneity of the soil microbes, providing a more exact narrative of the microbes present in each slope and spatiotemporal trends of microbial life in the landscapes

Evolution of Perturbation in Quiescent Medium

Here, the perturbation equation for a dissipative medium is derived from the first principle from the linearized compressible Navier-Stokes equation without Stokes's hypothesis. The dispersion relations of this generic governing equation are obtained for one and three-dimensional perturbations, which exhibit both the dispersive and dissipative nature of the perturbations traveling in a dissipative medium, depending upon the length scale. We specifically provide a theoretical cut-off wave number above which the perturbation equation represents diffusive and dissipative nature. Such behavior has not been reported before, as per the knowledge of the authors.Comment: 12 page 1 figure. arXiv admin note: substantial text overlap with arXiv:2212.1379

Functional Predictions of Microbial Communities in Soil as Affected by Long‐term Tillage Practices

Core Ideas Microbial function is important but difficult to assess in soil. An omics‐driven tool, PICRUSt, was used to characterize functions of soil microbial communities. No‐tillage compared with plow tillage was functionally enriched for most nutrient cycles. Many other functions integral to soil health can be explored by the PICRUSt omics approach. Soil microbial communities affect the soil\u27s biological, chemical, and physical properties, but there is still a knowledge gap regarding the long‐term impact of tillage practices on soil microbial dynamics. Additionally, the accurate identification of belowground microbial functions is a topic of active interest. In this study, microbial community profiles and functions in soil from a 50‐plus‐year‐old experiment in Ohio, representing one of the world\u27s longest running comparisons of a plow‐tillage system and a continuous no‐tillage system, were compared. The Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) algorithm was used to predict associated functional traits from 16S rRNA gene sequences. Analysis of the sequences revealed a large number of unidentified operational taxonomic units (67%), which is consistent with expectations of the soil ecosystem. Next, we investigated gene and enzyme predictions for nitrogen, sulfur, and methane metabolism and hydrocarbon degradation in soil. Results indicated that no‐tillage was functionally enriched for most nutrient cycles. This study has allowed us to predict distinct functional profiles as a result of legacy land uses. It serves as an example of improved analysis of the functional differences in soil managed by long‐term tillage versus no‐till

Bacterial community dissimilarity in soils is driven by long-termland-use practices

Land‐use practices impact soil microbial functionality and biodiversity, with reports suggesting that anthropogenic activities potentially result in reduced microbial functions and loss of species. The objective of this study was to assess the effect of long‐term (\u3e50 yr) land use (natural forest and grassland, and agricultural land) on soil bacterial community structure. A high‐throughput sequencing‐by‐synthesis approach of the 16S rRNA gene was used to study bacterial community and predicted functional profiles of Alfisols, as affected by variables including land‐use (forest, grass, agricultural) and soil/crop management (rotation and tillage) in long‐term experimental plots in Hoytville, OH. The distribution of the abundant phyla was different across samples. No‐till soils showed higher diversity indices than the plow‐till (PT) soils. Ordinations across locations suggested that no‐till soils had distinctly different community structure compared with plow‐till soils, while crop rotation within the no‐till plot had highest number of taxa. Overall land use (forest, grass, agronomic treatment) and tillage (within agricultural soils) were found to be significant when evaluating bacterial community dissimilarity. Predictive functional profiles showed that the forest soil had greatest proportion of PICRUSt‐assignable gene functions followed by the no‐till and grassland soils whereas plow‐till soils had the lowest predicted gene abundances across all samples. The results provide a view of soil bacterial diversity and predictive functional capacity in long‐term land‐use and soil/crop management practices, with a potential to inform future experiments to increase our understanding of long‐term impacts of land use on microbial community structure and function

Characterization of the DNA-binding domain and identification of the active site residue in the ‘Gyr A’ half of Leishmania donovani topoisomerase II

DNA topoisomerase II is a multidomain homodimeric enzyme that changes DNA topology by coupling ATP hydrolysis to the transport of one DNA helix through a transient double-stranded break in another. To investigate the biochemical properties of the individual domains of Leishmania donovani topoisomerase II, four truncation mutants were generated. Deletion of 178 aminoacids from the C-terminus (core and LdΔC1058) had no apparent effect on the DNA-binding or cleavage activities of the enzymes. However, when 429 aminoacids from the N-terminus and 451 aminoacids from the C-terminus were removed (LdΔNΔC), the enzyme was no longer active. Moreover, the removal of 429 aminoacids from the N-terminus (LdΔNΔC, core and LdΔN429) render the mutant proteins incapable of performing ATP hydrolysis. The mutant proteins show cleavage activities at wide range of KCl concentrations (25–350 mM). In addition, the mutant proteins, excepting LdΔNΔC, can also act on kDNA and linearize the minicircles. Surprisingly, the mutant proteins fail to show the formation of the enhanced cleavable complex in the presence of etoposide. Our findings suggest that the conformation required for interaction with the drug is absent in the mutant proteins. Here, we have also identified Tyr(775) through direct sequencing of the DNA linked peptide as the catalytic residue implicated in DNA-breakage and rejoining. Taken together, our results demonstrate that topoisomerase II are functionally and mechanistically conserved enzymes and the variations in activity seem to reflect functional optimization for its physiological role during parasite genome replication