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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 The purpose of this study is to analyse numerically and experimentally the effects of lip thickness (LT) and bypass ratio on co-flowing nozzle under subsonic and correctly expanded sonic jet decay at different Mach numbers. Design/methodology/approach Co-flowing jets from co-flowing nozzles of different LTs, 0.2, 1 and 1.5 Dp (where Dp is the primary nozzle exit diameter = 10 mm), with an annular gap of 10 mm at main jet exit Mach numbers 0.6 have been studied experimentally and the other cases have been performed numerically. The co-flowing jet with 2 mm LT was used for comparison. Findings Co-flowing jet axial pitot pressure decay, axial static pressure decay, axial velocity decay, radial velocity decay and streamline velocity contours were analyzed. The results illustrate that the mixing of the co-flowing jet with profound LT is prevalent to the co-flowing jet with 2 mm LT, at all Mach numbers of the current study. Also, the LT of the co-flowing jet has a strong impact on jet mixing. Co-flowing jets with 10 mm and 15 mm LT with a constant co-flow width of 10 mm experience a considerably advanced mixing than co-flowing jets with 2 mm LT and a co-flow width of 10 mm. Practical implications The application of bypassed co-flow jet is in turbofan engine operates efficiently in modern civil aircraft. Originality/value All subsonic jets are considered correctly expanded with negligible variation in axial static pressure. However, in the present study, static pressure along the centerline varies sinusoidally up to 9% and 12% above and below atmospheric pressure, respectively, for primary jet exit Mach number 1.0. The sinusoidal variation is less for primary jet exit Mach numbers 0.6 and 0.8 in static pressure decay.

The characteristics of a sonic under-expanded coaxial jet with lip thickness 1.5D p (where D p is the exit diameter of primary jet equals 10 mm) with the primary jet operating at nozzle pressure ratio (NPR) of 3, 4 and 5. For NPR 3 operating primary jet, the secondary jet operates at NPR 2.5, 1.4 and 1.27. For primary jet NPR 4, the secondary jet operating NPR is 3.2, 1.6 and 1.4. For NPR 5 primary jet, the secondary jet NPR is 3.8, 1.89 and 1.52. The study is performed using a co-flow nozzle of bypass ratio (BR) 6.4, 1.4 and 0.7. The core length of the primary jet is used as a measure to quantify the mixing of the primary jet in the presence of coaxial jet. The shock structure present in the near field was viewed using shadowgraph technique. Centreline pitot pressure distribution, radial spread and waves present in the jet core were analyzed. The results show that the mixing associated with the high bypass coaxial jet is superior to the low bypass coaxial jet. This mixing superiority associated with high bypass coaxial jet prevails all levels of expansion.

Hypersonic vehicles attain a speed five times more high-speed than the speed of sound, which is beyond Mach 5 and nearly equal to 6174km/h. Hypersonic flow has certain characteristics, essentially a reedy shock layer, formation of entropy layer, viscous interactions, high temperature, and low-density flow. Only if these characteristics are subjected in the flow can the flow can be called hypersonic. While designing a hypersonic flight vehicle, the characteristics of the hypersonic atmosphere should be understood clearly. This comes as a major design constraint. A brief overview of the hypersonic vehicle design and high-speed flow characteristics will be presented in this chapter. A few characteristics of hypersonic flow and the ideal design conditions will also be reviewed.

Aerofoil noise as self-noise is detrimental to system performance, in this paper NACA 0012 optimization parameters are presented for reduction in noise. Designing an aerofoil with little noise is a fundamental objective of designing an aircraft that physically and functionally meets the requirements. Aerofoil self-noise is the noise created by aerofoils interacting with their boundary layers. Using neural networks, the suggested method predicts aerofoil self-noise. For parameter optimization, the quasi-Newtonian method is utilised. The input variables, such as angle of attack and chord length, are used as training parameters for neural networks. The output of a neural network is the sound pressure level, and the Quasi Newton method further optimises these parameters. When compared to the results of regression analysis, the values produced after training a neural network are enhanced.

Effect of Mach number on coflowing jet at lip thickness of 0.2 Dp, 1.0 Dp and 1.5 Dp (where Dp is primary nozzle exit diameter, 10 mm) at Mach numbers 1.0, 0.8 and 0.6 were studied experimentally. It was found that an increase in Mach number does not have any profound effect on axial total and static pressure variation for 0.2 Dp. Decreasing the mean diameter is due to the geometrical constraints. In this study, the primary nozzle dimension and secondary duct is maintained constant for comparison. For the case of 0.2 Dp, static pressure is almost equal to atmospheric pressure for all Mach numbers. Whereas for other two lip thickness, increase in Mach number marginally influences axial total pressure and profoundly varies static pressure. It is noted that it varies considerably up to 11.1% in the axial direction and up to 17% in the radial direction for Mach number 1.0. For lower Mach numbers, such variation is not observed. Increase in Mach number increases static pressure variation in the coflowing jet flow field with lip thickness 1.0 Dp and 1.5 Dp.

Background: Hemiarthroplasty has been accepted as the treatment of choice for displaced femoral neck fractures. In the recent years the use of bone cement in hemiarthroplasty had become a controversial topic as few studies had recommended the use of uncemented hemiarthroplasty because of its minimal complications. Aim: To compare and assess the efficacy of cemented and uncemented bipolar hemiarthroplasty prosthesis among patients with femoral neck fractures. Methodology: A prospective comparative study was conducted at our hospital from the department of Orthopaedics for a period of one year. Patients aged more than 18 years of age of any gender with fracture neck of femur were included as study subjects. A total of 60 patients were included as our study subjects. It was divided into two groups of 30 each, one group received the cemented and the other group underwent an uncemented hemiarthroplasty. Patients were followed up on the 6th postoperative week for radiological assessment of the implant position and further advised for complete weight bearing as tolerated. Subsequently patients were followed up at 3rd and 12th month. At each visit patient was assessed for recovery based on harris hip score which includes post operative pain, return to activities of daily living, shortening of limb, range of movements, deformity and gait. Results: The duration of surgery was found to be longer in the cemented group with a mean duration of 82.8 mins and among the un-cemented group it was 63.6 mins. The intra-operative blood loss in 60% of the patients among the cemented group had more than 300 ml whereas among the un-cemented group it was only 13.3% had more than 300 ml of blood loss. The mean Harris hip score at the end of 12 months among the cemented group was 81.6 and among the un-cemented group it was 79.07 and both the groups showed a statistical significant improvement in their scores when compared to the score at 3 months whereas no significant difference observed in the scores between the two groups. Conclusion: Both the cemented and uncemented hemiarthroplasty are equally good options in the treatment of fracture neck of femur among elderly patients with minimal complications among the two methods. More data comparing uncemented and cemented hemiarthroplasty in patients with femoral neck fracture are still needed to substantiate our findings.

Depression is one of the most common chronic mental illnesses globally and in India. It has been reported that depression is twice as common in individuals with type 2 diabetes. The prevalence of both depression and type 2 diabetes are rapidly increasing. This article reviews the prevalence of depression in the general population as well as in patients with type 2 diabetes and its complications with special reference to recent data from India. It also makes a case for screening for depression in diabetes clinics and integrating depression treatment with diabetes care in order to make the treatment more wholistic.