Sathish Kumar K., Senthilkumar Chidambaram and Naren Shankar Radha Krishnan
This paper aims to present the jet mixing effectiveness of triangular tabs with semi-circular corrugations to control the subsonic and sonic correctly expanded jets.
Abstract
Purpose
This paper aims to present the jet mixing effectiveness of triangular tabs with semi-circular corrugations to control the subsonic and sonic correctly expanded jets.
Design/methodology/approach
Three semi-circular corrugated triangular tabs (Tab A, Tab B and Tab C) of equal blockage 5.11% are used, in which the corrugation locations on the tabs are varied. The offset distance between the semi-circular corrugations at the leaned edges of the triangular tabs are 0.0, 0.75 and 1.5 mm for the Tabs A, B and C, respectively. Two identical semi-circular corrugated tabs has been placed exactly 180° apart at the exit of the convergent nozzle. The pitot pressure measurements were taken to study the jet mixing characteristics of the tabs for the jet exit Mach numbers of 0.6, 0.8 and 1.0, and it is compared with the free jet.
Findings
The jet centerline pitot pressure decay reveals that, Tab A is very effective than Tab B and Tab C. For the jet exit Mach numbers of 0.6, 0.8 and 1.0, the potential core reduction for the Tab A is found to be 69.1%, 69.7% and 70.8%, respectively, when compared with the free jet.
Practical implications
The semi-circular corrugated triangular tabs were found to be more effective than the plain triangular tabs of equal blockage ratio for reducing the core length with minimum thrust loss.
Originality/value
The offset distance of the semi-circular corrugations are varied along the leaned sides of the triangular tabs, which is the novelty of this study.
Details
Keywords
Sathish Kumar K. and Senthilkumar Chidambaram
The purpose of this study is to increase the jet mixing effectiveness of Mach 1.6 axisymmetric jet using semi-circular corrugated triangular tabs (Tabs A, B and C), in which the…
Abstract
Purpose
The purpose of this study is to increase the jet mixing effectiveness of Mach 1.6 axisymmetric jet using semi-circular corrugated triangular tabs (Tabs A, B and C), in which the locations of the semi-circular corrugations are varied along the leaned sides of the triangular tabs.
Design/methodology/approach
The tabs are fixed at the exit of the nozzle facing each other 180° apart. To quantify the jet mixing effectiveness of the semi-circular corrugated tabs, Pitot pressure measurements were carried out for the cases of over-expansion, marginally over-expansion and under-expansion levels of Mach 1.6 jet, along the jet centerline and the jet spread, along and normal to the tab axis.
Findings
The results exhibit that the semi-circular corrugated Tab A augments the jet mixing when compared to Tabs B and C. This impact in jet mixing is strongly due to the small-scale vortices shed from the tabs and the mixed effect of the corrugation locations and expansion ratio. The maximum percentage reduction in core length is about 73.6 per cent for the jet with semi-circular corrugated Tab A at NPR 5, whereas it is 71.4 and 67.1 per cent for Tabs B and C, respectively.
Practical implications
The reduction in core length of the jet with minimum thrust loss is obtained by controlling the jet used with semi-circular corrugated triangular tabs of equal blockage ratio 5.12 per cent with respect to the nozzle exit diameter.
Originality/value
The locations of the semi-circular corrugations varied systematically at the equally leaned sides of the triangular tab ensure the novelty of this study.
Details
Keywords
Suresh V., Kathiravan Balusamy and Senthilkumar Chidambaram
An experimental investigation of hemispherical forebody interaction effects on the drag coefficient of a D-shaped model is carried out for three-dimensional flow in the…
Abstract
Purpose
An experimental investigation of hemispherical forebody interaction effects on the drag coefficient of a D-shaped model is carried out for three-dimensional flow in the subcritical range of Reynolds number 1 × 105 ≤ Re ≤ 1.8 × 105. To study the interaction effect, hemispherical shapes of various sizes are attached to the upriver of the D-shaped bluff body model. The diameter of the hemisphere (b1) varied from 0.25 to 0.75 times the diameter of the D-shaped model (b2) and its gap from the D-shaped model (g/b2) ranged from 0.25 to 1.75 b2.
Design/methodology/approach
The experiments were carried out in a low-speed open-circuit closed jet wind tunnel with test section dimensions of 1.2 × 0.9 × 1.8 m (W × H × L) capable of generating maximum velocity up to 45 m/s. The wind tunnel is equipped with a driving unit which has a 175-hp motor with three propellers controlled by a 160-kW inverter drive. Drag force is measured with an internal six-component balance with the help of the Spider 3013 E-pro data acquisition system.
Findings
The wind tunnel results show that the hemispherical forebody has a diameter ratio of 0.75 with a gap ratio of 0.25, resulting in a maximum drag reduction of 67%.
Research limitations/implications
The turbulence intensity of the wind tunnel is about 5.6% at a velocity of 18 m/s. The uncertainty in the velocity and the drag coefficient measurement are about ±1.5 and ±2.83 %, respectively. The maximum error in the geometric model is about ±1.33 %.
ractical implications
The results from the research work are helpful in choosing the optimum spacing of road vehicles, especially truck–trailer and launch vehicle applications.
Social implications
Drag reduction of road vehicle resulting less fuel consumption as well as less pollution to the environment. For instance, tractor trailer experiencing approximately 45% of aerodynamics drag is due to front part of the vehicle. The other contributors are 30% due to trailer base and 25% is due to under body flow. Nearly 65% of energy was spent to overcome the aerodynamic drag, when the vehicle is traveling at the average of 70 kmph (Seifert 2008 and Doyle 2008).
Originality/value
The benefits of placing the forebody in front of the main body will have a strong influence on reducing fuel consumption.
Details
Keywords
Yang Yang, Weijing Zhang, Zheng Liu and Peihua Zhang
The purpose of this work is to investigate the effect of filament composition with different specifications on the thermal comfort properties of bi-layer knitted fabrics.
Abstract
Purpose
The purpose of this work is to investigate the effect of filament composition with different specifications on the thermal comfort properties of bi-layer knitted fabrics.
Design/methodology/approach
In this paper eight bi-layer knitted fabrics with the same knitting structure but different filament compositions were prepared, and the thermal-wet comfort properties of these fabrics were examined. According to experimental data, the effect of filament composition on the thermal comfort properties of fabric was analyzed.
Findings
The increasing difference of hydrophilicity between inner and outer layers resulted in the enhancement of moisture management properties. Better thermal-physiology performance was exhibited by fabrics made up of finer and circular section fibers. Excellent thermal transfer, drying performance and one-way water transport capacity benefited the improvement of dynamic cooling effect of fabrics.
Originality/value
This work provides a useful and effective method for the development of bi-layer knitted fabric applied for sports and summer clothing.