arXiv subjects

Somnath De

Publications and source records attributed to Somnath De.

16 recordsLinked to original sources

arXiv2025

Insights of Transitions to Thermoacoustic Instability in Inverse Diffusion Flame using Multifractal Detrended Fluctuation Analysis

The inverse diffusion flame (IDF) can experience thermoacoustic instability due to variations in power input or flow conditions. However, the dynamical transitions in IDF that lead to this instability when altering control parameters have not been thoroughly investigated. In this study, we explore the control parameters through two different approaches and employ multifractal detrended fluctuation analysis to characterize the transitions observed prior to the onset of thermoacoustic instability in the inverse diffusion flame. Our findings reveal a loss of multifractality near the region associated with thermoacoustic instability, which suggests a more ordered behavior. We determine that the singularity exponent, the width of the multifractal spectrum, and the Hurst exponent are reliable indicators of thermoacoustic instability and serve as effective classifiers of dynamical states in inverse diffusion flames.

physics.flu-dyn↗

arXiv2024

Identifying feedback directions in the mechanisms driving self-sustained thermoacoustic instability in a single-element rocket combustor

The occurrence of high frequency (>1000 Hz) thermoacoustic instability (TAI) sustained by mutual feedback among the acoustic field, heat release rate oscillations, and hydrodynamic oscillations poses severe challenges to the operation and structural integrity of rocket engines. Hence, quantifying the differing levels of feedback between these variables can help uncover the underlying mechanisms behind such high frequency TAI, enabling redesign of combustors to mitigate TAI. However, so far, no concrete method exists to decipher the varying levels of mutual feedback during high-frequency TAI. In the present study, we holistically investigate the mutual influence based on the spatiotemporal directionality among acoustic pressure, heat release rate, hydrodynamic and thermal oscillations during TAI of a single-element rocket engine combustor. Using symbolic transfer entropy (STE), we identify the spatiotemporal direction of feedback interactions between those primary variables when acoustic waves significantly emerge during TAI. We unveil the influence of vorticity dynamics at the fuel collar (or the propellant splitter plate) as the primary stimulant over the heat release rate fluctuations to rapidly amplify the amplitude of the acoustic field. Further, depending on the quantification of the degree of the mutual information (i.e., the net direction of information), we identify the switches in dominating the thermoacoustic driving between the variables during TAI, each representing a distinct mechanism of a thermoacoustic state. Additionally, from this quantification, we analyze the relative dominance of the variables and rank-order the mutual feedback according to their impact on driving TAI.

physics.flu-dyn↗

arXiv2022

A Deep Learning Approach to Detect Lean Blowout in Combustion Systems

Lean combustion is environment friendly with low NOx emissions and also provides better fuel efficiency in a combustion system. However, approaching towards lean combustion can make engines more susceptible to lean blowout. Lean blowout (LBO) is an undesirable phenomenon that can cause sudden flame extinction leading to sudden loss of power. During the design stage, it is quite challenging for the scientists to accurately determine the optimal operating limits to avoid sudden LBO occurrence. Therefore, it is crucial to develop accurate and computationally tractable frameworks for online LBO detection in low NOx emission engines. To the best of our knowledge, for the first time, we propose a deep learning approach to detect lean blowout in combustion systems. In this work, we utilize a laboratory-scale combustor to collect data for different protocols. We start far from LBO for each protocol and gradually move towards the LBO regime, capturing a quasi-static time series dataset at each condition. Using one of the protocols in our dataset as the reference protocol and with conditions annotated by domain experts, we find a transition state metric for our trained deep learning model to detect LBO in the other test protocols. We find that our proposed approach is more accurate and computationally faster than other baseline models to detect the transitions to LBO. Therefore, we recommend this method for real-time performance monitoring in lean combustion engines.

cs.LG↗

arXiv2022

Study of Interaction and Complete Merging of Binary Cyclones Using Complex Networks

Cyclones are amongst the most hazardous extreme weather events on Earth. When two co-rotating cyclones come in close proximity, a possibility of complete merger (CM) arises due to their interactions. However, identifying the transitions in the interaction of binary cyclones and predicting the merger is challenging for weather forecasters. In the present study, we suggest an innovative approach to understand the evolving vortical interactions between the cyclones during two such CM events using time-evolving induced velocity based unweighted directed networks. We find that network-based indicators, namely, in-degree and out-degree, can quantify the changes during the interaction between two cyclones and are better candidates than the traditionally used separation distance to classify the interaction stages before a CM. The network indicators also help to identify the dominating cyclone during the period of interaction and quantify the variation of the strength of the dominating and merged cyclones. Finally, we show that the network measures also provide an early indication of the CM event well before its occurrence.

physics.geo-ph↗

arXiv2021

Empirical determination of the energy loss of heavy quarks in nuclear collisions at RHIC and LHC energies

Heavy quarks produced in the heavy ion collisions loose energy while propagting in the hot partonic matter which finally fragment to heavy ($D$ or $B$) mesons. The energy loss suffered by the heavy quarks is imprinted in the nuclear modification factor as a function of transverse momenta ($p_T$) of these heavy mesons. An alternate measure of in-medium energy loss comes through the effective shift in transverse momentum spectra of hadrons recorded in nucleus-nucleus collisions when it is compared to the same in proton-proton collisions. We start by parametrizing invariant momentum yields of heavy mesons in p+p collisions. The fit function from p+p collisions and measured nuclear modification factor in heavy ion collisions are then utilised to obtain the shift in the transeverse mass $\Delta m_T$ of heavy mesons produced at the RHIC and LHC experiments.The energy loss $\Delta m_T$ so obtained is found to scale with the transverse mass ($m_T$) of heavy mesons through a power law at different energies and centralities of collisions. We have also calculated using theoretical formalism, the total energy loss suffered by a charm quark in quark-gluon plasma produced in Pb~+~Pb collisions at the LHC energies. The evolution of the plasma is described by (2+1) dimensional longitudinal boost-invariant ideal hydrodynamics. It is found that the total energy loss of charm quarks scales with the transverse mass of charm quarks through a similar power law which supports our empirical analysis of energy loss.

hep-ph↗

arXiv2018

Photon production from Pb+Pb collisions at {$\sqrt{s_{\rm {NN}}}$} = 5.02 TeV at LHC and at {$\sqrt{s_{\rm {NN}}}$} = 39 TeV at FCC

We calculate the production of prompt and thermal photons from Pb+Pb collisions at 5.02A TeV at the Large Hadron Collider (LHC) and at 39A TeV at the proposed Future Circular Collider (FCC) facility. The photon spectra and anisotropic flow at these energies are compared with the results obtained from 2.76A TeV Pb+Pb collisions at the LHC for three different centrality bins. The prompt photons originating from initial hard scatterings are found to increase by a factor of 1.5 to 2 at 5.02A TeV in the $p_T$ region 2 to 15 GeV and the enhancement is found to be about 5 to 15 times at FCC energy compared to 2.76A TeV in the same $p_T$ region. The evolution of the Quark-Gluon Plasma (QGP) formed in Pb+Pb collisions at LHC and FCC energies are studied using a hydrodynamical model and the $p_T$ spectra and elliptic flow of thermal photons are calculated using state-of-the-art photon rates. The relative enhancement in the production of thermal photons is found to be more compared to prompt photons at FCC than at the LHC energies. Although the production of direct (prompt+thermal) photons is found to enhance significantly with increase in beam energy, the photon elliptic flow increases only marginally and does not show strong sensitivity to the collision energy.

nucl-th↗

arXiv2017

Towards laboratory detection of topological vortices in superfluid phases of QCD

Topological defects arise in a variety of systems, e.g. vortices in superfluid helium to cosmic strings in the early universe. There is an indirect evidence of neutron superfluid vortices from glitches in pulsars. One also expects that topological defects may arise in various high baryon density phases of quantum chromodynamics (QCD), e.g. superfluid topological vortices in the color flavor locked (CFL) phase. Though vastly different in energy/length scales, there are universal features, e.g. in the formation of all these defects. Utilizing this universality, we investigate the possibility of detecting these topological superfluid vortices in laboratory experiments, namely heavy-ion collisions. Using hydrodynamic simulations, we show that vortices can qualitatively affect the power spectrum of flow fluctuations. This can give unambiguous signal for superfluid transition resulting in vortices, allowing for check of defect formation theories in a relativistic quantum field theory system, and the detection of superfluid phases of QCD. Detection of nucleonic superfluid vortices in low energy heavy-ion collisions will give opportunity for laboratory controlled study of their properties, providing crucial inputs for the physics of pulsars.

hep-ph↗

arXiv2016

Thermalization of dense hadronic matter in Au + Au collisions at the energies available at FAIR

The conditions of local thermodynamic equilibrium of baryons (non-strange, strange) and mesons (strange) are presented for central Au + Au collisions at FAIR energies using the microscopic transport model UrQMD. The net particle density, longitudinal-to-transverse pressure anisotropy and inverse slope parameters of the energy spectra of non-strange and strange hadrons are calculated inside a cell in the central region within rapidity window $|y| < 1.0$ at different time steps after the collision. We observed that the strangeness content is dominated by baryons at all energies, however contribution from mesons become significant at higher energies. The time scale obtained from local pressure (momentum) isotropization and thermalization of energy spectra are nearly equal and found to decrease with increase in laboratory energy. The equilibrium thermodynamic properties of the system are obtained with statistical thermal model. The time evolution of the entropy densities at FAIR energies are found very similar with the ideal hydrodynamic behaviour at top RHIC energy.

nucl-th↗

arXiv2016

The effect of neutron skin on inclusive prompt photon production in Pb~+~Pb collisions at the LHC

Recent experiments on lead (\textrm{$Pb_{82}^{208}$}) nuclei have observed the celebrated phenomenon of neutron skin-thickness of low energy nuclear physics. The skin-thickness provides a measure of extension of spatial distribution of neutrons inside the atomic nucleus than protons. We have studied the effect of neutron skin-thickness on inclusive prompt photon production in Pb~+~Pb collisions at the Large Hadron Collider energies. We have calculated the \textquoteleft central-to-peripheral ratio\textquoteright ($R_\textrm{cp}$) of prompt photon production with and without accounting for neutron skin effect. The neutron skin causes a characteristic enhancement in the ratio, in particular at forward rapidity, which is distinguishable in our calculation. However a very precise direct photon measurement up to large transverse momenta would be necessary to constrain the feature in experiment.

nucl-th↗

arXiv2014

Jet-Triggered Photons from Back-Scattering Kinematics for Quark Gluon Plasma Tomography

High energy photons created from back-scattering of jets in quark gluon plasma are a valuable probe of the temperature of the plasma, and of the energy loss mechanism of quarks in the plasma. An unambiguous identification of these photons through single inclusive photon measurements and photon azimuthal anisotropies has so far been elusive. We estimate the spectra of back-scattering photons in coincidence with trigger jets for typical kinematic situations at the Large Hadron Collider and the BNL Relativistic Heavy Ion Collider. We find that the separation of back-scattering photons from other photon sources using trigger jets depends crucially on our ability to reliably estimate the initial trigger jet energy. We estimate that jet reconstruction techniques in heavy ion experiments need to be able to get to jet $R_{AA}\gtrsim 0.7$ in central collisions for viable back-scattering signals.

nucl-th↗

arXiv2013

Extent of sensitivity of single photon production to parton distribution functions

We have studied the production of single isolated prompt photons in high energy proton-proton collisions at the RHIC ($\sqrt{s}$= 200 GeV) and the LHC ($\sqrt{s}$= 7 TeV) energies within the frame work of perturbative QCD upto next-to leading order of strong coupling ($α_s$). We have used five different parameterizations of parton distribution function (PDF) starting from the old CTEQ4M to the new CT10 distributions and compared our results with the recent single prompt photon data from the PHENIX and the CMS collaborations. The prompt photon cross-section is found to be described equally well by all the PDF's within the experimental errors at the RHIC and the LHC energies. The deviation in the prompt photon yield for different PDF sets is within $\pm$ 20% when compared to CTEQ4M. The diphoton measurement could be a potential candidate to constrain the gluon distribution inside the proton.

hep-ph↗

arXiv2013

Nuclear modification of charged hadron production at LHC

We analyze the recent results for suppressed production of charged hadrons for Pb+Pb collisions at the center of mass energy of 2.76 TeV/nucleon-pair. We closely follow the treatment used recently by us where partons lose energy due to radiation of gluons following multiple scatterings while traversing the quark gluon plasma, before fragmenting into hadrons at the center of mass energy of 200 GeV/nucleon-pair. We obtain an empirical value for the momentum transport coefficient $(\widehat{q})$ and provide predictions for azimuthal anisotropy of hadron momenta for non-central collisions.

nucl-th↗

arXiv2012

Jet-Tagged Back-Scattering Photons For Quark Gluon Plasma Tomography

Direct photons are important probes for quark gluon plasma created in high energy nuclear collisions. Various sources of direct photons in nuclear collisions are known, each of them endowed with characteristic information about the production process. However, it has been challenging to separate direct photon sources through measurements of single inclusive photon spectra and photon azimuthal asymmetry. Here we explore a method to identify photons created from the back-scattering of high momentum quarks off quark gluon plasma. We show that the correlation of back-scattering photons with a trigger jet leads to a signal that should be measurable at RHIC and LHC.

nucl-th↗

arXiv2011

System size dependence of nuclear modification and azimuthal anisotropy of jet quenching

We investigate the system size dependence of jet-quenching by analyzing transverse momentum spectra of neutral pions in Au+Au and Cu+Cu collisions at $\sqrt{s_{\textrm{NN}}}$ =200 GeV for different centralities. The fast partons are assumed to lose energy by radiating gluons as they traverse the plasma and undergo multiple collisions. The energy loss per collision, $ε$, is taken as proportional to $E$(where $E$ is the energy of the parton), proportional to $\sqrt{E}$, or a constant depending on whether the formation time of the gluon is less than the mean path, greater than the mean free path but less than the path length, or greater than the path length of the partons, respectively. NLO pQCD is used to evaluate pion production by modifying the fragmentation function to account for the energy loss. We reproduce the nuclear modification factor $R_\textrm{AA}$ by treating $ε$ as the only free parameter, depending on the centrality and the mechanism of energy loss. These values are seen to explain the nuclear modification of prompt photons, caused by the energy lost by final state quarks before they fragment into photons. These also reproduce the azimuthal asymmetry of transverse momentum distribution for pions within a factor of two and for prompt photons in a fair agreement with experimental data.

nucl-th↗

arXiv2011

Dynamics of Quark Gluon Plasma and Interference of Thermal Photons

The quantum statistical interference between identical particles emitted from a completely chaotic source is expected to provide valuable input for the space time description of the system. Intensity interferometry of thermal photons produced in heavy ion collisions is a very promising tool to explore the structure and dynamics of the collision fireball. Thermal photons having $K_T \, \le \, 2$ GeV/$c$ get competing contribution from both hadronic and quark matter phases and this competition gives rise to a rich structure in the outward correlation function, owing to the interference between the photons from the two sources. The temporal separation between the two sources provides the lifetime of the system and the correlation results are found to be sensitive to quark hadron phase transition temperature and the formation time of the plasma. The outward correlation function strongly depends on the equation of state of the strongly interacting matter and is seen to clearly distinguish between the lattice based and bag model equations of state.

nucl-th↗

arXiv2010

Equation of state of strongly interacting matter: spectra for thermal particles and intensity correlation of thermal photons

We find that an equation of state for hot hadronic matter consisting of all baryons having $M < 2$ GeV and all mesons having $M < 1.5$ GeV, along with Hagedorn resonances in thermal and chemical equilibrium, matches rather smoothly with lattice equation of state (p4 action, ${N_τ}=8$) for T up to $\approx 200$ MeV, when corrected for the finite volume of hadrons. Next we construct two equations of state for strongly interacting matter; one, HHL, in which the above is matched to the lattice equation of state at $T=165$ MeV and the other, HHB, where we match it to a bag model equation of state with critical temperature $T_c=165$ MeV. We compare particle spectra, thermal photon spectra and histories of evolution of the quark-gluon plasma produced in the central collision of gold (lead) nuclei at RHIC (LHC) energies, considering ideal hydrodynamical expansion of the system. The particle and thermal photon spectra are seen to differ only marginally, for the two equations of state. The history of evolution shows differences in the evolution of temperature and radial velocity, as one might expect. We calculate intensity interferometry of thermal photons and find it to be quite distinct for the two equations of state, especially for the outward correlation. The longitudinal correlation also shows a dependence on the equation of state, though, to a smaller extent.

nucl-th↗