https://libjncir.jncasr.ac.in/xmlui/handle/10572/10 2026-04-04T05:30:29Z 2026-04-04T05:30:29Z Mukund, V. Singh, D. K. Ponnulakshmi, V. K. Subramanian, Ganesh Sreenivas, K. R. https://libjncir.jncasr.ac.in/xmlui/handle/10572/2449 2017-02-21T10:25:22Z 2014-01-01T00:00:00Z

Field and laboratory experiments on aerosol-induced cooling in the nocturnal boundary layer Mukund, V.; Singh, D. K.; Ponnulakshmi, V. K.; Subramanian, Ganesh; Sreenivas, K. R. Heat transfer processes in the nocturnal boundary layer (NBL) influence the surface energy budget and play an important role in many micrometeorological processes, including the formation of inversion layers, radiation-fog and in the control of air-quality near the ground. Under calm and clear-sky conditions, radiation plays an important role in determining the characteristics of the NBL. In this article, we report observations, close to ground, of hypercooling that has a radiative origin, and which leads to anomalous vertical temperature profiles with elevated minima. In addition, a laboratory experimental set-up is developed that is capable of capturing the thermal structure of the NBL, close to ground, under various conditions. Results from the laboratory experiments indicate that the high cooling rates near the ground, observed in the field experiments, arise from a near-surface heterogeneity in the (aerosol-laden) NBL; a feature ignored in radiation models used for atmospheric simulations. Many of these models nevertheless predict preferential near-ground cooling in apparent agreement with our field observations. However, the cooling is spurious, and arises from the use of an incorrect frequency-averaged transmittance in the radiation model. Based on our observations, a non-dimensional number is proposed that characterizes the evolution in the lowest metres of the NBL; in particular, the effect of radiation on the NBL thermal structure. Our results should help in parametrizing NBL transport process, and highlight the need to account for both the effects of aerosols close to the ground and a varying ground emissivity, via appropriate boundary conditions in general circulation and climate models. Restricted Access

2014-01-01T00:00:00Z Chao, Liu Kwak, Sang Kyu Ansumali, Santosh https://libjncir.jncasr.ac.in/xmlui/handle/10572/2448 2017-02-21T10:25:16Z 2014-01-01T00:00:00Z

DIRECT SIMULATION MONTE CARLO FOR DENSE HARD SPHERES Chao, Liu; Kwak, Sang Kyu; Ansumali, Santosh We propose a modified direct simulation Monte Carlo (DSMC) method, which extends the validity of DSMC from rarefied to dense system of hard spheres (HSs). To assess this adapted method, transport properties of hard-sphere (HS) systems have been predicted both at dense states as well as dilute, and we observed the excellent accuracy over existing DSMC-based algorithms including the Enskog theory. The present approach provides an intuitive and systematic way to accelerate molecular dynamics (MD) via mesoscale approach. Restricted Access

2014-01-01T00:00:00Z Krithivasan, Siddharth Wahal, Siddhant Ansumali, Santosh https://libjncir.jncasr.ac.in/xmlui/handle/10572/2447 2017-02-21T10:25:14Z 2014-01-01T00:00:00Z

Diffused bounce-back condition and refill algorithm for the lattice Boltzmann method Krithivasan, Siddharth; Wahal, Siddhant; Ansumali, Santosh A solid-fluid boundary condition for the lattice Boltzmann (LB) method, which retains the simplicity of the bounce-back method and leads to positive definite populations similar to the diffusive boundary condition, is presented. As a refill algorithm, it is proposed that quasi-equilibrium distributions be used to model distributions at fluid nodes uncovered due to solid movement. The method is tested for flow past an impulsively started cylinder and demonstrates considerable enhancement in the accuracy of the unsteady force calculation at moderate and high Reynolds numbers. Furthermore, via simulations, we show that momentum exchange procedure used in LB to compute forces is not Galilean invariant. A modified momentum exchange procedure is proposed to reduce the errors due to violation of Galilean invariance. Restricted Access

2014-01-01T00:00:00Z Mudigere, Dheevatsa Sherlekar, Sunil D. Ansumali, Santosh https://libjncir.jncasr.ac.in/xmlui/handle/10572/2446 2017-02-21T10:25:10Z 2014-01-01T00:00:00Z

Delayed Difference Scheme for Large Scale Scientific Simulations Mudigere, Dheevatsa; Sherlekar, Sunil D.; Ansumali, Santosh We argue that the current heterogeneous computing environment mimics a complex nonlinear system which needs to borrow the concept of time-scale separation and the delayed difference approach from statistical mechanics and nonlinear dynamics. We show that by replacing the usual difference equations approach by a delayed difference equations approach, the sequential fraction of many scientific computing algorithms can be substantially reduced. We also provide a comprehensive theoretical analysis to establish that the error and stability of our scheme is of the same order as existing schemes for a large, well-characterized class of problems. Restricted Access

2014-01-01T00:00:00Z