http://dspace.dtu.ac.in:8080/jspui/handle/123456789/109 2026-07-25T11:52:36Z http://dspace.dtu.ac.in:8080/jspui/handle/repository/23009 Title: ANALYSIS OF SWIRLING FLOW IN ANNULAR DIFFUSER Authors: PRIYA; Arora, B. B. (supervisor) Abstract: In today’s rapidly advancing world, there is an increasing demand for devices that are energy-efficient, safe, and cost-effective. Available usable energy resources are depleting quickly, creating an urgent need to address this challenge. One possible solution is to develop techniques that can convert otherwise unusable energy into useful forms. However, creating such methods often requires significant effort, and in many cases, the outcomes may not justify the cost or may lack economic feasibility. An alternative and more practical approach is to conserve existing resources by designing energy-efficient systems that minimize energy losses. A diffuser is one such device that plays an important role in energy conservation. It converts the kinetic energy of a flowing fluid—energy that would otherwise be lost—into an increase in static pressure. In turbomachinery systems used for power generation, annular diffusers are commonly employed. These diffusers typically operate under conditions where the incoming flow may contain varying degrees of swirl. Therefore, improving their performance is essential and requires systematic investigation. Experimental research on annular diffusers is often challenging due to the need for advanced instrumentation and complex, time-intensive procedures, making such studies costly and limiting the extent of research in this field. The present study combines both experimental and analytical approaches to investigate the aerodynamic behaviour of axial annular diffusers. A specialized test setup was developed to introduce different levels of inlet swirl. Measurements were conducted v using a three-hole cobra probe to determine static pressure distribution, axial velocity, and swirl velocity profiles at various sections along the diffuser length. In addition to experimental work, computational analysis was carried out using CFD modelling. The study includes grid independence testing and the selection of an appropriate turbulence model that closely matches experimental observations as well as results reported in existing literature. After validation, the CFD model was used to analyse flow characteristics in two types of annular diffusers: one with a parallel hub and diverging casing, and another with both hub and casing diverging at equal angles. Both diffuser configurations were studied for equivalent cone angles of 10° and 20°, and area ratios of 2 and 3. The influence of inlet conditions—specifically velocity profiles with and without swirl angles of 7.5°, 12°, 17°, and 25° — was examined to evaluate diffuser performance. Detailed flow behaviour was analysed, and key performance parameters were calculated. The development of the flow was studied to identify regions of flow separation and reversal within the diffuser. The effects of various factors, including inlet swirl, area ratio, diffuser geometry, and cone angle, were systematically analysed to understand their impact on flow separation and overall performance. The results indicate that inlet swirl has an optimal value that maximizes diffuser performance. This optimal swirl level depends on the geometry and configuration of the diffuser. 2026-06-01T00:00:00Z http://dspace.dtu.ac.in:8080/jspui/handle/repository/22995 Title: FATIGUE FAILURE ANALYSIS OF LOW-PRESSURE STEAMTURBINE BLADE Authors: NITIN; Rani, Sushila (SUPERVISOR) Abstract: Steam turbine blades are the most vital and critical components in the power plants for electricity generation as they convert heat energy into mechanical work. A single failure of a blade can cause the complete shutdown of a plant. Low pressure (LP) blades are exposed to critical working conditions of large centrifugal forces, and dynamic forces due to changing steam loads along with corrosive effects that contribute to the susceptibility of LP blades to fatigue failure. Thus, in particular, L-0 stage blades are most susceptible to fatigue and fracture type of failures. Therefore, the reliability and performance of LP blades depend on preventing or understanding such failures. This paper provides a comprehensive review of fatigue failure behavior of low-pressure steam turbine blades using both an experimental investigation and an integrated computational and residual stress analysis. A failure analysis of a martensitic stainless-steel alloy X10CrNiMoV 12-2-2, L-0 stage low-pressure steam turbine blade was conducted in this research. A transverse crack existed at the leading edge of the blade that propagated toward the trailing edge of the blade. Detailed examinations of the morphology and origin of the crack were performed using a combination of mechanical testing, fractographic examination utilizing scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), and visual inspections. The microstructural examination showed a disturbed martensitic structure which is typical of a heat-treated turbine-grade steel and SEM fractography showed typical fatigue striations and intergranular cracking. The EDS results confirm the presence of corrosion promoting products such as chlorine, silicon and oxygen and Sio2 particles on the fracture surface of the blade which results in corrosion fatigue a predominant failure mode. A residual stress analysis was conducted to gain a further insight into the internal stress conditions that contribute to the initiation and propagation of cracks, using a µ-X360 FULL 2D portable X ray residual stress analyzer that relies on the cos v α method of analysis. The findings showed that tensile residual stresses on the blade surface exist, which are the reason for stress concentrators and enhance fatigue crack development during cyclic loading. The residual stresses that were generated during the manufacturing and service in operation were discovered to have a major impact on the fatigue performance and life of the blade. The stress distribution at steady operational loading was assessed by means of the static structural analysis to determine the potential regions that are critical and could fail during operation. Dynamic analysis was also used to calculate the natural frequencies and critical speeds of the blades by Campbell diagrams, to avoid resonance at start-up and shut-down periods. The simulations of fatigue crack propagation were possible with the help of a hybrid computational method combining ANSYS and FRANC 3D. The rubber box method in FRANC 3D was used to create a sub model with a template radius of 0.5 mm and an initial edge crack of 2 mm and then the evolution of stress intensity factors KI was analyzed through a series of load cycles. The driving force that controlled the crack propagation was assessed using the stress intensity factor KI and the simulated fatigue life was about 38,414 cycles. When the loading continued, KI reached a maximum of approximately 3640 MPa√mm at the 86th step, which was greater than the fracture toughness of the material and signified the beginning of an unstable crack propagation. The findings emphasize the importance of advanced simulation tools in predicting the fatigue behaviour of LPST blade in order to minimize the catastrophic consequences associated with failure. In addition to providing an integrated understanding of fatigue failure in low-pressure steam turbine blades via a correlation of metallurgical studies, residual stress distributions, and computational fracture mechanics; the study also shows that both tensile residual stress and vibrational resonance contribute to the failure of these blades; as well as corrosion fatigue. 2026-06-01T00:00:00Z http://dspace.dtu.ac.in:8080/jspui/handle/repository/22776 Title: THERMODYNAMIC PERFORMANCE AND DESIGN OF SMALL-SCALE H2O-LiBr VAPOR ABSORPTION SYSTEM FOR ROOM AIR COOLING Authors: MISHRA, SHOBHIT; Singh, Raj Kumar (SUPERVISOR) Abstract: The present study addresses the research gap in small-scale distributed trigeneration systems by investigating two novel configurations: (1) a solar power tower (SPT) driven helium Brayton cycle (HBC) integrated with a heat recovery steam generator (HRSG) and a vapor absorption cooling system (VACS), and (2) a solid oxide fuel cell-gas turbine (SOFC-GT) hybrid system coupled with a vapor absorption refrigeration system (VARS). The primary objectives of this thesis are: (i) to develop and simulate a novel SPT-HBC-HRSG-VACS trigeneration system for combined power, heating, and cooling; (ii) to perform comprehensive energy and exergy analysis of the proposed trigeneration system; (iii) to develop a SOFC-GT-VARS cogeneration system for small-scale room air conditioning; and (iv) to investigate the energy, exergy, economic, and environmental (4E) performance of the SOFC-GT-VARS system. The SPT-HBC-HRSG-VACS system exploits waste heat from a basic HBC driven by an SPT. The two subsystems, HRSG and VACS, recover waste heat for steam generation and air conditioning cooling, respectively. A comprehensive exergy and energy analysis of this proposed trigeneration system was carried out with parametric analysis using Engineering Equation Solver (EES) software. It was concluded that energy and exergy efficiency and net work output of the proposed trigeneration system were observed as 44.96%, 34.15%, and 14,562 kW respectively. The heating production through the HRSG was obtained as 8,510 kW while the cooling production by VACS was 115.10 kW. Moreover, the coefficient of performance (COP) of the VACS subsystem was observed as 0.8015. Energy and exergy efficiency of the SPT-operated basic HBC using the subsystems were improved by 58.98% and 12.92%, respectively. Parametric analysis revealed that the helium turbine inlet temperature and solar heliostat field efficiency significantly affect the trigeneration system performance. vi For the second configuration, a novel SOFC-GT-VARS system for combined cooling and power generation is developed. Thermodynamic, economic, and environmental analyses were performed on the proposed system using computational techniques. The proposed plant obtained power output, exergy efficiency, and energy efficiency of 551.29 kW, 48.03%, and 50.18%, respectively, at given operating conditions. The cooling effect of 5.275 kW (1.5 TR) was obtained from the VARS with a COP of 0.752. The total cost rate of the proposed plant was observed as 33.57 $/h, while the CO₂ emission per MWh of energy output was obtained as 394.70 kg/MWh. The research successfully fills the identified gaps in small-scale distributed trigeneration systems and provides a comprehensive framework for evaluating such systems under Indian climatic and economic conditions. 2025-07-01T00:00:00Z http://dspace.dtu.ac.in:8080/jspui/handle/repository/22758 Title: EXPERIMENTAL AND NUMERICAL INVESTIGATIONS ON LASER FORMING OF MULTI-LAYERED CLAD SHEET METAL Authors: SINGH, PRAVEEN KUMAR; GAUTAM, VIJAY (SUPERVISOR) Abstract: The effectiveness of the laser forming process is strongly dependent on the interaction of thermal and mechanical properties inherent in a clad sheet comprising different layers having different properties. The present research examines how laser power, scanning speed, and number of passes at two distinct levels of maximum and minimum affect the bend angle in the samples of a two-ply clad sheet comprising SS430 and AA1050 layers. The clad sheet, was chosen because of its demand in precision manufacturing for performance attributes like as corrosion resistance, thermal conductivity, and mechanical strength. A central composite design was carried out to determine the correlation between the input variables and output response. Design-Expert software was employed to design the experiments, which gave 20 runs to conduct the tests. Response surface methodology was incorporated to optimize the results. The results obtained by analysis of variance were found to be in agreement with the results obtained by experiments. An optimized combination of 900 W laser power, with number of scans and velocity of 60 and 30 mm/s, respectively resulted in a maximum bend angle of 39° with a relative error of 2.14%. The effect of laser bending due to multiple scans on the clad sheet along the laser path in the thickness direction was also examined to understand the microstructure and texture evolution by electron backscattered diffraction technique. The irradiated surface is affected the most and the texture becomes poor whereas, the layer of AA1050 below the irradiated surface improved in texture. It is also observed that the residual stress in the innermost layer of SS430 is of compressive nature whereas the stress in the outermost layer of AA1050 is tensile in nature. The microhardness in the laser-irradiated zone of the SS430 layer ranges from 200 HV to a maximum of 272 HV, whereas the hardness in the AA1050 layer across the bent zone does not vary significantly. 2025-12-01T00:00:00Z