https://dr.ddn.upes.ac.in//xmlui/handle/123456789/3070 Wed, 13 May 2026 10:14:41 GMT 2026-05-13T10:14:41Z https://dr.ddn.upes.ac.in//xmlui/handle/123456789/4233 Title: Computational solvers for iterative hydraulic loss calculations in pipe systems Authors: Dwivedi, Ayush; Sawant, Gorakh; Karn, Ashish Abstract: The study of fluid mechanics spans several engineering disciplines including Mechanical, Civil, Aerospace, Chemical, Environmental, Petroleum, and Biomedical Engineering. In all these disciplines, hydraulic loss calculations in pipes are extremely important. However, the iterative nature of the solution to these engineering problems makes it intricate and cumbersome to solve. This further makes it difficult to visualize the solutions to such iterative problems for a wide variety of cases. The current paper aims to bridge this gap by the creation of two open-source Excel-VBA based computational solvers. The first tool corresponds to the determination of the Darcy-Weisbach friction factor through the Colebrook Equation and its visualization on a Moody’s chart, which can be effectively employed by engineering instructors as an active learning tool. Second, a complete tool covering all four kinds of pipe flow situations (including the iterative problems) has been developed. The developed computational tool was employed in an undergraduate Fluid Mechanics classroom and the detailed student responses were collected on ten aspects related to teaching and learning divided broadly under four categories – ‘overall rating’, ‘student perceptions on self-learning’, ‘Improvement in teaching delivery’, and ‘recommendation for other courses’. The data collected from student responses were subjected to statistical analysis. The results of hypothesis testing and the p-value calculations clearly justify the immense usefulness of this tool in the overall teaching-learning process of Fluid Mechanics. Finally, the developed computational tools are being hosted free on the web for the benefit of engineering instructors, learners and professionals alike. Description: Paper published in the journal "Journal of Engineering Education Transformations" , 2022, 35(4) Fri, 01 Apr 2022 00:00:00 GMT https://dr.ddn.upes.ac.in//xmlui/handle/123456789/4233 2022-04-01T00:00:00Z https://dr.ddn.upes.ac.in//xmlui/handle/123456789/4232 Title: Investigation of ventilation demand variation in unsteady supercavitation Authors: Yoon, Kyungduck; Li, Jiaqi; Shao, Siyao; Karn, Ashish; Hong, Jiarong Abstract: Understanding the air injection strategy of a ventilated supercavity is important for designing high-speed underwater vehicles wherein an artificial gas pocket is created behind a flow separation device to reduce skin friction. Our study systematically investigates the effect of flow unsteadiness on the ventilation requirements to form (CQf ) and collapse (CQc) a supercavity. Imposing flow unsteadiness on the incoming flow has shown an increment in higher CQf at low free stream velocity and lower CQf at high free stream velocity. High-speed imaging reveals distinctly different behaviors in the recirculation region for low and high freestream velocity under unsteady flows. At low free stream velocities, the recirculation region formed downstream of a cavitator shifted vertically with flow unsteadiness, resulting in lower bubble collision and coalescence probability, which is critical for the supercavity formation process. The recirculation region negligibly changed with flow unsteadiness at high free stream velocity and less ventilation is required to form a supercavity compared to that of the steady incoming flow. Such a difference is attributed to the increased transverse Reynolds stress that aids bubble collision in a confined space of the recirculation region. CQc is found to heavily rely on the vertical component of the flow unsteadiness and the free stream velocity. Interfacial instability located upper rear of the supercavity develops noticeably with flow unsteadiness and additional bubbles formed by the distorted interface shed from the supercavity, resulting in an increased CQc. Further analysis on the quantification of such additional bubble leakage rate indicates that the development and amplitude of the interfacial instability accounts for the variation of CQc under a wide range of flow unsteadiness. Our study provides some insights on the design of a ventilation strategy for supercavitating vehicles in practice. Description: Paper published in the journal Experimental Thermal and Fluid Science, 129 (2021), 110472 Mon, 01 Nov 2021 00:00:00 GMT https://dr.ddn.upes.ac.in//xmlui/handle/123456789/4232 2021-11-01T00:00:00Z https://dr.ddn.upes.ac.in//xmlui/handle/123456789/4231 Title: On the morphology of elongated bubbles during their formation at submerged orifices Authors: Gaurav, Kumar; Mittal, Gaurav; Karn, Asish Abstract: Bubbly flow is a widely observed phenomenon in various industrial applications and has remained a topic of sustained interest over decades, owing to the complex multi-physics that govern the multiphase phenomenon. The bubble geometrical morphology and dynamics critically depend on various parameters such as flow rate, orifice diameter, working fluid properties, and height of the fluid above the orifice. Accordingly, experiments are conducted in water, acetone, and Glycerol-water solutions (10% w/w and 20% w/w) using a sub-millimeter submerged orifice of diameter 0.4 mm, 0.6 mm, and 1 mm. The volume flow rate is varied in the range of 100–300 ml per min and experiments are carried out at varying orifice depths of 4 – 12 cm. The dynamics of bubble formation is recorded by high-speed cinematography and is processed using MATLAB script. This paper presents the bubble rise and coalescence morphology and the effect of operating parameters on it. The gas injection and bubble geometrical parameters can be expressed in terms of non-dimensional numbers such as Reynolds number, Weber number, Froude number, and Eotvos number. It is found that simple scaling laws can be established among Reynolds number with Weber number, Froude number, and their ratio, which can effectively predict the bubble geometry. It is found that the relation between the ratio of Weber and Froude number to Reynolds number depends on the height of fluid above the orifice. The present work also quantifies the interconnection between Reynolds number and Eotvos number and demonstrates a relationship that is incumbent on the gas superficial velocity. In particular, it is observed that the slope of the Re-Eo curve decreases with the increase in the gas superficial velocity. Description: Paper published in the journal Chemical Engineering Science, 250 (2022), 117395 Tue, 15 Mar 2022 00:00:00 GMT https://dr.ddn.upes.ac.in//xmlui/handle/123456789/4231 2022-03-15T00:00:00Z https://dr.ddn.upes.ac.in//xmlui/handle/123456789/4230 Title: Mechanism of vortex bifurcation vis-à-vis axial switching in rectangular synthetic jets Authors: Kumar, Abhay; Saha, Arun K.; Panigrahi, Pradipta K.; Karn, Ashish Abstract: The present study investigates the vortex dynamics of the rectangular shaped synthetic jet and reports the occurrence of vortex ring bifurcation along with other reported modes such as axial switching and the vortex suction. The novel finding of vortex ring bifurcation of rectangular synthetic jets has been observed without any other mode of excitation except the periodic axial actuation. The experiments on synthetic jets have been conducted at different actuation frequencies and both qualitative and quantitative characterization of the flow structures has been carried out using Laser Induced Fluorescence (LIF) and Laser Doppler Velocimetry, respectively. LIF flow visualization provides insights into the size of the vortex and the vortex evolution with respect to time, enabling us to propose the flow physics behind the axial switching and the vortex bifurcation processes for rectangular synthetic jets. The proposed flow physics is then quantitatively evidenced by the time-averaged velocity measurements. Vortex splitting or bifurcation is found to occur in the minor axis plane of orifice and the divergence angle depends on the actuation frequency and average velocity of fluid expelled through the orifice in the forward stroke of diaphragm. In the case of occurrence of axial switching, a maximum of three axial switching events are observed before vortex breakup. Finally, by systematically carrying out experiments across a wide range of operational parameters, a narrow region corresponding to the vortex bifurcation has been identified on a Reynolds Number–Strouhal Number map, along with other modes such as axial switching regime and the vortex suction regime. Based on our measurements, a mechanism of vortex bifurcation vis-à-vis axial switching has also been suggested. Description: Paper published in the journal European Journal of Mechanics - B/Fluids, 86 (2021), Pp. 78-89 Thu, 01 Apr 2021 00:00:00 GMT https://dr.ddn.upes.ac.in//xmlui/handle/123456789/4230 2021-04-01T00:00:00Z