Khizar Ahmed Pathan

Occurrence of sudden expansion is widespread in the defense and automobile industry. At the blunt base of the fuselage, missiles, projectiles, and aircraft bombs, the flow gets separated at the base and forms low-pressure recirculation, leading to a significant increase in the base drag. This paper addresses how this low base pressure at the base can be controlled. A detailed numerical study was conducted to assess the impact of the quarter circle as a passive control mechanism in a suddenly expanded flow for an area ratio of 4.84 at Mach M = 2.0 for various rib radii ranging from 1 mm to 4 mm, the different duct lengths from L = 1D to 6D at different nozzle pressure ratio ranging from 3 to 11. The findings of this study show that a 1 mm rib is inadequate to impact the flow field inside the duct. Passive control in the form of a quarter circle rib seems to become effective once the nozzle flows under a favorable pressure gradient. However, the remaining rib radii effectively reduce the suction created at the base of the recirculation zone. It is found that the rib radius of 4 mm when placed at 66 mm at the base, results in a maximum rise in the base pressure, and the base pressure ratio attains a value of 3.4. These results are case sensitive; hence, one has to make a final decision about the rib radius, rib location, and the level of expansion based on the end user requirement.

This investigation primarily underscores the numerical modeling of damping derivative across a two-dimensional wedge at diverse pivot points, particularly for considerable Mach numbers and angles of incidence values. The damping derivative is simulated numerically via regression model analysis. Analytical results are derived by employing Ghosh's two-dimensional piston theory. This study considers factors including Mach number, wedge angle, and pivot position. The current inquiry observes that the wedge angle (θ) spans from 3° to 30°, whereas the Mach number (M) fluctuates between 5.5 and 10.0. Damping derivatives results are acquired through the examination of various Mach numbers (M) and angles of incidence (θ) at multiple pivot locations (h) ranging from 0.0 to 1.0. This research evaluates the damping derivative findings against theoretical forecasts, revealing a notable correlation between them. Research results and theoretical predictions exhibit a remarkable resemblance; however, this study demonstrates that changes in damping derivative are influenced by factors such as Mach number (M), angle of the wedge (θ), and position of the pivot (h). At every pivot position, the damping derivative magnitude diminishes with an increase in Mach number; however, it ascends with an increase in the angle of incidence. This phenomenon is noteworthy because it underscores the complex interplay between these variables (factors), although one might posit that the relationship could be more linear under certain conditions.

This study assesses the effectiveness of passive control as a quarter circle at Mach M = 1 for a duct of diameter 22 mm of length L = 1D to 6D. The study was conducted for a nozzle pressure ratio of 1.5 to 5. At sonic Mach M = 1, when the passive control is placed at various locations in the duct, the optimum location and radius of the rib seem to be 1D, 1.5D, 2D, and 4 mm, resulting in a base pressure almost double the ambient pressure for orientation1 of the rib where flow from the Nozzle sees curved part of the rib. The base pressure equals the ambient pressure for a 3 mm rib radius at 1D, 1.5D, and 2D. When the rib is located at 0.5D, there is an increase in the base pressure due to the presence of the rib. However, the base pressure magnitude is lower than attained for 1D, 1.5D, 2D, and 3D rib locations. The best options for orientation 2 of the rib locations are 1.5D and 2D. No appreciable results are obtained when the rib is placed at 3D for both orientations.

Occurrence of sudden expansion is widespread in the defence and automobile industry. At the blunt base of the fuselage, missiles, projectiles and aircraft bombs, the flow gets separated at the base and forms low-pressure recirculation, leading to a significant increase in the base drag. This paper addresses how this low base pressure at the base can be controlled. In this study, quarter circle ribs are used as a control mechanism to regulate the base pressure in a suddenly expanded flow of area ratio 4.84, Mach M = 1.8 for nozzle pressure ratios (NPRs) ranging from 3 to 11 at various rib locations in the range from 11 mm, 22mm, 33 mm, 44 mm and 66mm for duct length ranging from L = 1D to 6D. Results show for 11 mm rib location and 1 mm rib radius, there is a declining trend in the base till nozzle pressure ratio of 6 and for further increases in the expansion level, there is a progressive increase in the base pressure ratio. The highest base pressure value is 2 for a 4 mm rib radius at the highest simulated nozzle pressure ratio. This trend continues for 22 mm rib locations. With a further shift in the rib location, there is a considerable increase in the base pressure ratio. These values are 2.5, 3 and 3.75 for rib locations at 33 mm, 44 mm and 66 mm for a rib radius of 4 mm at the highest level of under-expansion. It is seen that even though the effectiveness of the 1 mm rib radius was nil for all the rib locations except when the rib is located at 66 mm. When a quarter circle rib of radius 1 mm is used, there is a significant increase in the base pressure and base suction is nearly zero. This study is a technology demonstration and the database created from this study can be used to design aerospace vehicles. It will be beneficial at the initial design stage as a wind tunnel test is costly.

The study of base pressure and its control is an important research area in the transonic speed when the flow undergoes a sudden change in area. The turbulent flow in a separated region is still a crucial area of research due to the advent of space shuttles and high-performance military aircraft, and turbulent flow in transonic and supersonic flow is a thrust area for researchers. This paper focuses on base pressure control with sudden expansion at Mach 1.3 for an area ratio of 4.84. The flow field inside the duct is controlled through a passive control in the form of quarter ribs of radii 1 mm, 2 mm, 3 mm, and 4 mm for various duct lengths in the range from L = 1D to 6D for nozzle pressure ratios in the range from 3 to 11. Results show that a 1 mm rib is not adequate, and rib radii 2 mm, 3 mm, and 4 mm are effective in raising the base pressure values, and this rise in the base pressure continues till the duct length L = 1D to 4D. There is a marginal reduction in base pressure for the duct lengths L = 5D and 6D due to the ineffectiveness of the back pressure.

This paper discusses the control of base pressure by passive means, where the jet is issued from a converging nozzle at sonic Mach number under a favorable pressure gradient. The effect of employing annular ribs on the enlarged duct and its impact on the flow field, as the passive control mechanism from a converging nozzle at the sonic Mach number, is investigated numerically in this study. The velocity distribution and base pressure changes are analyzed using a numerical compressible turbulence flow model. Initially, the rib is positioned at 16 mm (1D) from the base of the duct. Later, the rib position is shifted from 1D to 2D and then to 3D and 4D. The effect of variation of the rib positions, as well as its height from 1 mm to 3 mm, keeping the width of the rib fixed to 3 mm, is studied. The nozzle pressure ratio varies from 1.5 to 5, and the rib location is 1D and 2D. The velocity variation in the duct with and without rib placement is also analyzed. The results revealed comprehensive spread observations from the positive analysis of base pressure variation in ducts with no ribs and ribs with heights of 1 mm and 2 mm. The base pressure increased significantly with increasing nozzle pressure ratio for both rib heights compared to a smooth duct. It is also deduced that the highest base pressure is achieved at an aspect ratio of 3:1 when placed at 4D.

Wet steam flow produces big water droplets in the low-pressure zone of a steam turbine blade. These droplets clash with subsequent blades, resulting in a strong impact that is evident as erosion. Titanium and its alloys are valuable for technical applications such as turbine blades because of their low density, high strength, and exceptional corrosion resistance. The boron carbide(B4C) has a high hardness but a low strength; therefore, it's exciting to investigate water erosion of Ti/ B4C and SiC combination. The effect of 1 wt% B4C and 1, 3, 5, and 7 wt% SiC particles on water droplet erosion of Ti composite was studied using the SPS method for 5 minutes at 1200 oC temperature and 50 MPa pressure. The L9 orthogonal array with four levels of parameters of the Taguchi method is used to conduct the experiments. By measuring the weight of the specimen at interval time, the erosion behavior with time is obtained with different nozzle diameters. The effect of material and experimental parameters on erosion resistance is studied, and an empirical relation is developed.

Photovoltaic thermal (PVT) systems, when combined with nanoparticle-enhanced phase change materials (NePCM-nanofluid), significantly enhance energy efficiency in solar thermal applications. This study introduces a mathematical model for a nanofluid/NePCM PVT system, validated by experimental data. The model demonstrates electrical and thermal efficiencies of 14.50% and 70%, respectively, closely aligning with experimental results of 14% and 69.40%. The maximum temperatures observed are 43.1°C for glass, 42.60°C for the PV cell, 42°C for wax, and 41.8°C for the nanofluid. These findings underscore the model's accuracy and its practical potential for optimizing PVT systems in high-temperature environments.

The stringent norms imposed by the government to reduce emissions to the environment have forced all engine manufacturers to reduce engine emissions. Carbon monoxide and NOx emissions from diesel engines are topics of significant consideration. This causes climate change and natural calamities. The current paper focuses on the comparative performance optimization of single-cylinder engines in DI and HCCI mode fitted with custom-designed catalytic converters in Series configuration using Taguchi regression Analysis based on experimental results obtained for series combination. The present work tested a diesel engine in both DI and HCCI modes with catalytic converters in series configurations with various monolith lengths and compression ratios. The test results are then analyzed using the Taguchi method and regression analysis. Overall, BTE is higher for HCCI mode than DI mode with the series arrangement of catalytic converters in the 24% to 35% range. Meanwhile, BSFC is lower for HCCI mode, in the 20% to 64% range. Hydrocarbon emission is higher, starting from 15% to 48%. The NOx emissions are lower for lower load, but on full load, they are more than those in DI Mode. CO emissions are also Higher for HCCI mode in the 12% to 30% range.