A numerical tool for predicting the spatial decay of freestream turbulence.

The present numerical work is an attempt towards modelling of freely decaying homogeneous isotropic turbulence with its application in experimental modelling of the effect of incident turbulence on flow around 2D and 3D bluff-bodies. Both steady, Reynolds Averaged Navier Stokes (RANS) and unsteady, Large Eddy Simulation (LES), 3-D numerical computational fluid dynamics (CFD) techniques have been employed to characterise the inviscid decay of large-scale turbulence in terms of the characteristic r.m.s turbulent velocity fluctuations ( ) and the local integral length scale (Lu). The large-scale turbulent properties extracted from the current numerical simulations are inter-related and are shown to behave predominantly as Saffman turbulence, which states Lu3 ≈ constant. The other focus from the current study was on modelling inlet conditions for bluff-bodies in a freestream flow. A set of three-correlation equations are formulated based on the large-scale turbulent properties that are effective in estimating the initial and local freestream turbulence conditions. The set of prediction equations can be deemed useful for researchers developing wind-tunnel models in the presence of freestream turbulence. Additionally, the set of equations is also reliable in determining appropriate near-constant turbulent conditions based on the upstream inlet conditions. The current study aims at designing the region of constant turbulent properties of a desired magnitude that can be helpful for boundary layer and heat transfer studies over a bluff-body

A Prediction Tool For Spatially Decaying Freestream Turbulence

Paper presented at 2018 Canadian Society of Mechanical Engineers International Congress, 27-30 May 2018.A set of new correlation equations characterizing the spatial decay of isotropic homogeneous turbulence has been formulated in the current study. The correlation equations are based on the results from the current numerical simulations combined with data from earlier relevant experimental studies [10], [15], [16]. The correlation equations can be effective for predicting the local values of turbulent properties (turbulence intensity (TI) and integral length scale (Lu)) from well specified initial conditions and, similarly, the magnitudes of inlet turbulence (TI and Lu) can be estimated from the local magnitudes of length scale and turbulent kinetic energy (TKE) using the same prediction methodology. The set of prediction tools should be useful in the design of wind tunnel experiments to characterize bluff body aerodynamics in response to different incident turbulence conditions

Dynamic simulation of activated sludge based wastewater treatment processes: Case studies with Titagarh Sewage Treatment Plant, India

STOAT has been extensively used for the dynamic simulation of an activated sludge based wastewater treatment plant in the Titagarh Sewage Treatment Plant, near Kolkata, India. Some alternative schemes were suggested. Different schemes were compared for the removal of Total Suspended Solids (TSS), b-COD, ammonia, nitrates etc. A combination of IAWQ#1 module with the Takacs module gave best results for the existing scenarios of the Titagarh Sewage Treatment Plant. The modified Bardenpho process was found most effective for reducing the mean b-COD level to as low as 31.4 mg/l, while the mean TSS level was as high as 100.98 mg/l as compared to the mean levels of TSS (92 62 mg/l) and b-COD (92.0 mg/l) in the existing plant. Scheme 2 gave a better scenario for the mean TSS level bringing it down to a mean value of 0.4 mg/l, but a higher mean value for the b-COD level at 54.89 mg/l. The Scheme Final could reduce the mean TSS level to 2.9 mg/l and the mean b-COD level to as low as 38.8 mg/l. The Final Scheme looks to be a technically viable scheme with respect to the overall effluent quality for the plant. (C) 2009 Elsevier B.V. All rights reserved

Simulation of the effect of various operating parameters for the effective separation of carbon dioxide into an aqueous caustic soda solution in a packed bed using lattice Boltzmann simulation

Nowadays, reduction of the carbon footprint in the environment is one of the most challenging issues, and thus several technologies have been adopted for the effective arrest of carbon dioxide (CO2). Among these, packed-bed absorption using caustic soda is one of the simplest and widely accepted separation strategies for CO2. However, the intricate issues that make the process a bit complicated are the selection of operational parameters such as gas velocity or the caustic concentration for efficient separation. Moreover, the most significant one is the blockage of the pores within the packed-bed column that lead to a reduction in the effective mass-transfer area and, therefore, less separation. In order to analyze these operational paradigms, one needs to explore the process internal fluid dynamics pattern for long-term operation. In this present work, an attempt was made to enumerate this flow field in a packed bed using a lattice Boltzmann simulation technique, an extended concept of lattice gas automata. Moreover, using the simulation technique, the gas inlet velocity to the column and the caustic soda concentration were estimated for effective CO2 capture. The model shows a minimum absolute percentage error of 0.0005 between the predicted and experimental CO2 outlet concentration