Research

Vortex-induced vibrations (VIV) are induced on a bluff body when it is introduced to a fluid flow, which produces vortex shedding. Many times, the presence of VIV attributed due to vortex shedding is considered undesirable since it leads to fatigue induced damage on structural elements. The phenomenon of VIV is an important consideration, especially for offshore structures which are usually made of cylindrical members. The present study investigates the suppression of vortex shedding past a fixed cylinder using streamlined fairings and short-tailed fairings using a Computational Fluid Dynamics (CFD) solver based on Reynolds Averaged Navier-Stokes (RANS) equation. Fairings are relatively neutrally buoyant elements that are installed along the axis of long circular cylinders in order to lower drag force and to minimize VIV. The work aims at studying the vortex shedding pattern of a bare cylinder, cylinder with streamlined fairings and cylinder with short-tail fairing for various flow conditions. The hydrodynamic coefficients (e.g., lift coefficients, drag coefficients), and Strouhal number are key parameters that govern the vortex-induced vibration (VIV) on the cylindrical members.  Therefore, the study would also entail investigations on hydrodynamic lift and drag forces/coefficients. The range of Reynolds Numbers covered in the studies will be 1*104 < Re < 4*104. The study examines the influence of streamlined fairing and short-tail fairing in altering the vortex shedding behavior. The outcomes based on the study would help to understand the reduction in vortex shedding due to use of streamlined fairings in place of a fixed cylinder. This in turn would help in better design of offshore structures avoiding impacts due to VIV. 

Biogas, a renewable fuel, has low operational stability range in burners due to its inherent carbon-dioxide content. In cross-flow configuration, biogas is injected from a horizontal injector and air is supplied in an orthogonal direction to the fuel flow. To increase the stable operating regime, backward facing steps are used. Systematic numerical simulations of these flames are reported here. The comprehensive numerical model incorporates a chemical kinetic mechanism having 25 species and 121 elementary reactions, multicomponent diffusion, variable thermo-physical properties, and optically thin approximation based volumetric radiation model. The model is able to predict different stable flame types formed behind the step under different air and fuel flow rates, comparable to experimental predictions. Predicted flow, species, and temperature fields in the flames within the stable operating regime, revealing their anchoring positions relative to the rear face of the backward facing step, which are difficult to be measured experimentally, have been presented in detail. Resultant flow field behind a backward facing step under chemically reactive condition is compared against the flow fields under isothermal and non-reactive conditions to reveal the significant change the chemical reaction produces.