A new calculation formula to describe the dynamic pressure of water jet peening with elliptical nozzle for high-efficiency treatment

Water jet peening is a good potential method to control welding residual stresses. The water jet with elliptical nozzle can improve the treatment efficiency due to its large treatment area. In this article, the water jet velocity and dynamic pressure for different elliptical nozzle dimensions and standoff distances are discussed by numerical simulation. The results show that when the axial distance is 10 mm, the effective impact diameter of the elliptical nozzle a/b=8–12 is about 2 times or more than that of the circular nozzle. The length of the jet core of the elliptical nozzle is only related to the outlet structure and is independent of the inlet pressure. The correlation between the dimensionless core length of the elliptical water jet and its long and short axes is derived. When the ratio of the major axis to the minor axis is between 7 and 13, the core length of the elliptical water jet is 7–7.5 times that of its minor axis. Combining the suitable treatment area and dynamic pressure, the elliptical nozzle with an axis ratio of 8 is recommended to control the welding residual stress. Finally, a new formula for calculating dynamic pressure distribution is proposed for the elliptical nozzle water jet at different stages.

Effect of flat wall length on decay and shock structure of a supersonic square wall jet

Experiments were conducted to find the effect of wall length on the decay behaviour and shock structure of a supersonic wall jet issuing from c-d nozzle of the square-shaped exit. A straight flat wall of width same as the side length of the square was attached to the lip of the nozzle such that the leading edge of the wall and the side of the square aligned properly which allowed the supersonic jet to graze past the flat wall. Experiments were conducted with five different wall lengths, that is, [Formula: see text] = 0.5, 1, 2, 4 and 8. Wall pressure measurements were made from leading edge to the trailing edge of the wall along its centreline. Schlieren flow visualization of the jet flow over the wall for the different wall lengths revealed the shock pattern and the effect of the wall length on the shock structure. The shock structure and jet deflection were significantly affected due to the presence of the wall. There was an upward jet deflection for [Formula: see text] up to [Formula: see text] whereas a downward jet deflection was observed for [Formula: see text]. Noticeable changes in the shock structure were observed for the wall lengths up to 2 D h. The wall length also significantly affected the jet decay characteristics and supersonic core length. Maximum enhancement in jet decay and maximum reduction in supersonic core length resulted when the wall length was [Formula: see text]. However, when the wall length was increased to [Formula: see text], there was a significant reduction in jet decay and a recovery of [Formula: see text]. Presence of wall always resulted a reduction in Lsc irrespective of wall length. The wall effect was to induce a more precipitous pressure drop closer to the nozzle exit, and a more gradual drop farther from it for [Formula: see text] > [Formula: see text].

Mathematical simulation of air-water flow along Ski Jump Jet

In the present study, using a quasi 3D analytical simulation, air concentration distribution in ski jump generated jet is calculated. A numerical simulation is also performed to verify the results of the analytical model in parallel with the available experimental and another analytical data. By solving continuity and momentum equations in case of air-water flow for three different cases, it was confirmed that the air concentrations along the ski jet are uniquely linked to the relative black water core length. Results showed that the black water core length is also influenced by the approach flow depth, Froude number, geometrical parameters of ski jump and the chute bottom angle. Finally, an analytical equation is proposed to predict the air concentration distribution along the ski jump jet regarding different hydraulic and geometric parameters. By calculating the velocity profiles along the jet, it showed that increasing the air concentration reduces the jet velocity profile.

Influence of tab corner geometry on supersonic jets

Purpose The purpose of this study is to evaluate the effect of tabs having different corner geometries on the flow characteristics of a supersonic convergent–divergent (C-D) nozzle. Design/methodology/approach A circular C-D nozzle of Mach 2.0 was used, and the tabs were positioned at the exit of the nozzle in diametrically opposite directions. Three tabs having different corner geometry implemented in the experiments were rectangular tab with triangular top edge, triangular tab with a bell-shaped edge and tapered tab. The pressure profiles across the tabs and the centerline pressure decay along the jets were measured. The shadowgraph technique illustrated the waves present in the center of an oncoming jet. The nozzle pressure ratios (NPR) were varied from 4 to 8, in the steps of one, covering various overexpansion and under expansion levels at the exit of the nozzle. Findings The results showed tapered tabs act as a better mixing promoter than the other tabs used in the study. A reduction of 91.25% in core length for NPR 8 was observed for the tapered tabs. Subsequently, core length reductions generated by triangular tabs with a bell-shaped top edge were 87.5%, and those caused by rectangular tabs with a triangular top edge were 7.5%. Practical implications The research results could be used for designing combustion chambers and chemical reactors that require jets to enhance mixing levels. Originality/value The tabs having three different corners geometries, i.e. sharp or pointed, bell-shaped and straight edge has never been investigated before. The idea of only modifying corners is the innovative step of this research.

Species-Specific Differences in Sperm Chromatin Decondensation Between Eutherian Mammals Underlie Distinct Lysis Requirements

Sperm present a highly particular DNA condensation that is acquired during their differentiation. Protamines are key elements for DNA condensation. However, whereas the presence of protamine 1 (P1) is conserved across mammalian species, that of protamine 2 (P2) has evolved differentially, existing only few species that use both protamines for sperm DNA condensation. In addition, altered P1/P2 ratios and alterations in the expression of P1 have previously been associated to infertility and DNA damage disorders. On the other hand, different methods evaluating DNA integrity, such as Sperm Chromatin Dispersion (SCD) and Comet tests, need a previous complete DNA decondensation to properly assess DNA breaks. Related with this, the present study aims to analyze the resilience of sperm DNA to decodensation in different eutherian mammals. Sperm samples from humans, horses, cattle, pigs and donkeys were used. Samples were embedded in low melting point agarose and treated with lysis solutions to induce DNA decondensation and formation of sperm haloes. The treatment consisted of three steps: (1) incubation in SDS + DTT for 30 min; (2) incubation in DTT + NaCl for 30 min; and (3) incubation in DTT + NaCl with or without proteinase K for a variable time of 0, 30, or 180 min. How incubation with the third lysis solution (with or without proteinase K) for 0, 30, and 180 min affected DNA decondensation was tested through analyzing core and halo diameters in 50 sperm per sample. Halo/core length ratio was used as an indicator of complete chromatin decondensation. While incubation time with the third lysis solution had no impact on halo/core length ratios in species having P1 and P2 (human, equine and donkey), DNA decondensation of pig and cattle sperm, which only present P1, significantly (P < 0.05) increased following incubation with the third lysis solution for 180 min. In addition, the inclusion of proteinase K was found to accelerate DNA decondensation. In conclusion, longer incubations in lysis solution including proteinase K lead to higher DNA decondensation in porcine and bovine sperm. This suggests that tests intended to analyze DNA damage, such as halo or Comet assays, require complete chromatin deprotamination to achieve high sensitivity in the detection of DNA breaks.