Purpose This study aims to analyze co-flowing jets (CFJs) with constant velocity ratio (VR) and varying primary nozzle lip thickness (LT) to find a critical LT in CFJs below which mixing enhances and beyond which mixing inhibits. Design/methodology/approach CFJs were characterized with a constant VR and varying LTs. A single free jet with a diameter equal to that of a primary nozzle of the CFJ was used for characteristic comparison. Numerical simulation is carried out and is validated with the experimental results. Findings The results show that within a critical limit, the mixing enhanced with an increase in LT. This was signified by a reduction in potential core length (PCL). Beyond this limit, mixing inhibited leading to the elongation of PCL. This limit was controlled by parameters such as LT and constant VR. A new region termed as influential wake zone is identified. Practical implications In this study, the VR is maintained constant and bypass ratio (BR) was varied from low value to very high values. Presently, subsonic commercial turbo fan operates under low to ultra-high BR. Hence the present study becomes vital to the current scenario. Originality/value To the best of the authors’ knowledge, this is the first effort to find the critical value of LT for a constant VR for compressible co-flow jets. The CFJs with constant VR and varying LT have not been studied in the past. The present study focuses on finding a critical LT below which mixing enhances and above which mixing inhibits.

This chapter is focused on the roughness effect to evaluate the flow in order to examine the flow dynamics around airfoil for better aerodynamic efficiency. CFD analysis is done on the airfoil with circular roughness placed at two different positions, 25% and 65% chord length with two different Reynolds number. In this case, the boundary layer increased significantly due to decrease in velocity of flow resulting in increment of pressure gradient. From the computational and experimental investigation from many researchers, it is evident that adverse pressure gradient even becomes so large that the flow is forced back against the actual flow direction. In the current chapter, at 15 degrees angle of attack there was an effective increase of 65% in the aerodynamic efficiency due to roughness. There was an increase in stall angle, which refers to sudden increment of drag resulting from the aerodynamic and geometric variations over the infinite wing. With increase in Reynolds number, there is an increase in the effect of roughness at higher angles of attack.

Purpose In comparison to a nozzle with a larger/finite separation distance (Thanigaiarasu et al., 2019), a thin-lip nozzle (Srinivasarao et al., 2017) minimizes drag. Coaxial nozzles with thin lips are an appropriate tool for studying high subsonic jets because it does not create a dominant re-circulation zone. This study aims to analyze the characteristic of separation distances, between primary and secondary nozzles, within the range of 0.7–3.2 mm which can be considered a thin lip. Design/methodology/approach A separation distance of 0.7  (Papamoschou, 2004), 1.7  and 2.65 mm (Lovaraju and Rathakrishnan, 2011) is considered for the present study. The main nozzle exit Mach number is maintained at a subsonic condition of Mach 0.6, and the co-flowing nozzle exit Mach number is varied from 0% (secondary jet stopped/single jet) to 100% (Mach 0.6) in steps of 20% with respect to the main nozzle exit Mach number. A comparison was made between these velocity ratios for all three lip thicknesses in the present study. Design mesh and analysis were done by using Gambit 2.6.4 and Fluent 6.12. Velocity contours and turbulence contours were studied for qualitative analysis. Findings When lip thickness increases from 0.7 to 2.65 mm, the potential core length (PCL) of the primary jet decreases marginally. Additionally, the PCL of the primary jet elongates significantly as the velocity ratio increases. The primary shear layer is dominant at 20% co-flow (20 PCF), less dominant at 60% co-flow (60 PCF) and almost disappeared at 100% co-flow (100 PCF). Concurrently, the secondary shear layer almost disappeared in 20 PCF, dominant in 60 PCF and more dominant in 100 PCF. Different zones such as initial merging, intermediate and fully merged zones are quantitatively and qualitatively analyzed. Practical implications Co-flow nozzle is used in turbofan engine exhaust. The scaled-down model of a turbofan engine has been analyzed. Core length is directly proportional to the jet noise. The PCL signifies the jet noise reduction in a high-speed jet. For a low-velocity ratio, the potential core is reduced and hence can reduce the jet noise. At the same time, as the velocity ratio increases, the mass flow rate of the coaxial increases. The increase in the mass flow increases the thrust of the engine. The aircraft engine designer should analyze the requirement of the aircraft and choose the optimal velocity ratio coaxial nozzle for the engine exhaust (Papamoschou, 2004). Originality/value There have been many research studies carried out previously at various lip thickness such as 0.4  (Georgiadis, 2003), 0.7  (Papamoschou, 2004), 1.5  (Srinivasarao et al., 2014a), 1.7  (Sharma et al., 2008), 2  (Naren, Thanigaiarasu and Rathakrishnan, 2016), 2.65  (Lovaraju and Rathakrishnan, 2011), 3  (Inturiet al., 2022) and 3.2 mm (Perumal et al., 2020). However, there is no proper study to vary the lip thickness in this range from 0.7 to 3.2 mm to understand the flow behavior of a co-flowing jet.

Purpose This study aims to investigate the effect of slanted perforation diameter in tabs for the control of Mach 1.4 underexpanded supersonic jet flow characteristics. Design/methodology/approach Numerical investigation was carried out for NPR 5 to analyze the effect of slanted perforation diameter in tabs to control the Mach 1.4 jet. Four sets of tabs with slanted circular perforation geometries (Φp = 1, 1.5, 2 and 2.5 mm) were considered in this study. The inclination angle of 20° (αP) with reference to the jet axis was maintained constant for all the four tabs considered. Findings Determined value indicates there is a 68%, 71%, 73% and 75% drop in supersonic core for the Φp = 1, 1.5, 2.0 and 2.5 mm, respectively. The results show that the tabs with 2.5 mm perforation diameter were found to be efficient in reducing the supersonic jet core in comparison with other tab cases. The reduction in supersonic core length is due to the extent of miniscule vortices exuviating from slanted small and large diameter perforation in the tabs. Practical implications The concept of slanted perforation can be applied in scramjet combustion, which finds its best application in hypersonic vehicles and in noise suppression in fighter aircraft. Originality/value Slanted perforation and circular shapes with different diameters have not been studied in the supersonic regime. Examining the effect of circular diameter in slanted perforation is an innovation in this research paper.

Progress in future aeronautics depends purely on the new understandings of flow physics coupled with the interactions of various tools and disciplines. Emerging numerical computing tools and experimental aptitudes play a key role in the technological progress of aeronautical studies. This chapter presents an insight on the air foils, three-dimensional geometries attached to an airplane with an emphasis on computational tools. A countless number of small and large steps have taken place over many other disciplines. Design evolution has resulted in many geometrical changes in air foils, wings, fuselages, and stabilizers come in a whole range of shapes and sizes, both in the aerospace industry and in nature – really, nothing is standard. The application the airfoil operates and dictates its shape and size. Finite wing and infinite wing shapes are still sprouting today, driving the new challenging flight conditions. More efficient flights will drive the new and intelligent wing designs to obtain better load factor and reduced drag.