T. John Tharakan

Numerical study of air-core vortex dynamics during liquid draining from cylindrical tanks

An air core is often formed during liquid draining from cylindrical tanks. An understanding of the mechanism behind its formation and the parameters that accentuate its growth is central to the development of an air-core vortex suppression strategy. In the present study, liquid draining from a cylindrical tank is investigated with the aid of computational fluid dynamics tools. A qualitative and a quantitative comparison of the temporal variation of critical height against available experiments is reported. A systematic investigation has revealed that, drain port shape, size, pressurization, initial rotation, etc, play a vital role in the formation of an air core vortex and its growth. These variables were also observed to influence critical height and total drain time, both of which are of engineering interest. Towards the development of a gas-core suppression strategy, the circular drain port is modified to either a stepped or a bell mouth shape. Although the new drain port shapes have delayed the gas-core from entering the drain-port, they were found to be only marginally advantageous.

Trends in Comprehensive Modeling of Spray Formation

Comprehensive modeling of spray formation in liquid fuel injectors involves modeling of (i) internal hydrodynamics of fuel injector (ii) break up of liquid sheet leading to primary and secondary atomization and (iii) prediction of size and velocity distributions of droplets in the spray. Comprehensive models addressing all the three aspects are rare though some work has been reported that incorporate two of the three aspects. However, significant volume of literature exists on the individual modules. In the present work, progress and current trends in the individual modules have been extensively reviewed and their implications on development of comprehensive models have been discussed. The unresolved issues and future research directions are also indicated.

Influence of liquid and gas compressibility on the growth of waves in thin liquid sheets

The growth of waves along the direction of motion of viscous compressible liquid sheets in inviscid compressible gas streams was investigated. Gas streams were considered to move at different velocities relative to the liquid sheet. A dispersion relation was derived for the spatial growth of longitudinal waves in the presence of lateral wave modes. The solution of the dispersion relation showed that the incorporation of gas compressibility increases the growth of paraantisymmetric waves. Compressibility in liquid, such as obtained by the dispersion of gas bubbles, has a much lower influence on the growth of paraantisymmetric waves. The presence of lateral wave modes did not influence longitudinal wave growth when the compressibility of liquid and gas was considered in the model.

CFD Analysis of Water Cooled Flame Deflector in Rocket Engine Test Facility

The flame deflector of a rocket engine test facility needs to be protected from the high thermal loads resulting from the impingement of high velocity and high temperature exhaust flame on it during the hot test. The flame deflector is cooled by water injected from holes in the deflector plate. In this paper ANSYS Fluent was used to analyze the flow over the flame deflector. The engine plume structure and its impingement characteristics on the flame deflector were determined in the absence and presence of water injection. The water injection pattern was optimized for the better cooling of the deflector plate. SST k-ω model was used for the turbulence modelling. Discrete Phase Model was used to simulate water injection from holes provided in the impingement plate.

Spray characterisation using combined radon and hough transforms

The paper presents an improved injector spray characterization method using image analysis. The existing methods of image analysis such as granulometry and Hough transform are not efficient. The size of heavily overlapped spray particles cannot be accurately determined using granulometric methods. The Hough transform method is better in separating the overlapped droplets. But it produces erroneous data with smaller droplet sizes. Here, an improved method using both Radon and Hough transforms is presented to detect drop size distribution. In this method, Radon transform is used to differentiate between the overlapped and non-overlapped droplets and Hough transform to separate overlapped droplets. The proper segmentation of droplet regions are important in the accurate computation of Sauter mean diameter (SMD). As the segmentation by thresholding is affected by noise, an active contour based image segmentation using distance regularized level set evolution (DRLSE) is used for the segmentation of droplet regions. The proposed method is used to compute drop size distribution from the image of spray and corresponding histogram is also plotted. The result obtained is illustrated to be better than that obtained using Hough transform alone. Methods to detect spray cone angle and breakup length are also illustrated in this paper.