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Performance of corrugated actuator-tabs of aspect ratio 2.0 on supersonic jet mixing enhancement
Tamal Jana,Mrinal Kaushik 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.3
The present experimental investigation explores the ability of the corrugated actuator-tabs (or simply, the corrugated actuators) of aspect ratio 2 in encouraging the mixing of Mach 1.73 circular jet at different levels of expansion conditions. Essentially, rectangular, triangular, and semi-circular corrugated actuators are deployed at the opposite positions across the diameter of the nozzle outlet and compared with the plain or simple actuators located at the same positions. Quantitative and qualitative observations were conducted by pitot pressure measurements and shadowgraph flow visualization. Interestingly, the characteristic decays are higher for the semi-circular and triangular corrugated actuators, exhibiting superior mixing than the rectangular corrugated actuator in the far-field. However, the core length reduction for rectangular corrugation is greater than for triangular and semicircular corrugation geometry. As high as 96.5 % core length reduction was obtained for the rectangular corrugated actuators operating at the overexpansion condition. The pressure profiles along and perpendicular to these actuators confirmed that the deployment of the corrugation geometry significantly reduces the flow asymmetry. The shadowgraphic flow visualizations reveal that the plain and corrugated actuators weaken the waves and shorten the cells when compared to the uncontrolled or free jet.
Thermoelectric Properties of the Yttrium-Doped Ceramic Oxide SrTiO3
Tamal Tahsin Khan,어순철 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.70 No.1
The doping dependence of the thermoelectric figure of merit, ZT, of the ceramic oxide SrTiO3 at high temperature has been studied. In this study, yttrium was used as the doping element. A conventional solid-state reaction method was used for the preparation of Y-doped SrTiO3. The doping level in SrTiO3 was controlled to be in the doping range of 2 - 10 mole%. Almost all the yttrium atoms incorporated into the SrTiO3 provided charge carriers, as was observed by using X-ray diffraction pattern. The relative densities of all the samples varied from 98.53% to 99.45%. The thermoelectric properties, including the electrical conductivity σ, Seebeck coefficient S, thermal conductivity k, and the figure of merit, ZT, were investigated at medium temperatures. The ZT value showed an obvious doping level dependence, in which a value as high as 0.18 is realized at 773 K for a doping of 8 mole%.
Enhanced thermoelectric properties of the SrTiO3 by Zr-doping with different doping level
Tamal Tahsin Khan,김일호,어순철 한양대학교 세라믹연구소 2018 Journal of Ceramic Processing Research Vol.19 No.4
The enhancement of the thermoelctric properties of the SrTiO3 by doping with Zr were investigated in our study. The ZrdopedSrTiO3 with different doping level were synthesized by the conventional solid-state reaction method. The formation ofsingle phase cubic perovskite structure and the changing behavior of the average grain size confirmed that the Zr-dopedSrTiO3 were prepared to control doping level. The thermoelctric properties including Seebeck coefficient, electricalconductivity, and thermal conductivity has been investigated in a moderate temperature regime from 300 K to 1000 K. Theabsolute value of Seebeck coefficient decreased and the electrical conductivity increased monotonically with increasing dopinglevel. The thermal conductivity decreased with increasing doping level. The power factor increased with increasing dopinglevel-up to x = 0.03 mole and the dimensionless figure of merit ZT, increased up to x = 0.03 mole of Zr. The maximum ZT valuewas observed for SrTi0.97Zr0.03O3 at 873 K.
Jana Tamal,Thillaikumar T.,Kaushik Mrinal 한국항공우주학회 2020 International Journal of Aeronautical and Space Sc Vol.21 No.4
The supersonic/hypersonic flow through an aircraft intake must be decelerated before entering the combustion chamber to ensure efficient combustion. Retardation in the flow speed is achieved through a progression of oblique and normal shock waves in the isolator region of the intake. However, the advantages of speed reduction in intake are usually accompanied by huge losses due to the shock wave and boundary-layer interactions (SBLIs). These losses may include, inlet-unstart, abrupt thickening or separation of the boundary layer, unsteady shock oscillations, etc. Clearly, the SBLIs must be controlled to minimize the losses and improve the performance of the complete vehicle. Control of these interactions by manipulating the strength of the shock using a shallow cavity with wall ventilation has gained prominence. In this study, the efficacy of a thin porous surface deployed over shallow cavity in the higher adverse pressure gradient regions of Mach 5.7 and Mach 7.9 mixed-compression intakes, is experimentally investigated. With the variation of diameter and pitch of the pores, the porosity in Mach 5.7 intake is varied as; 4.5%, 7.5%, 17%, 21.6%, and 25%. A maximum of 20.53% drop in static pressure in the Mach 5.7 intake controlled by the cavity covered with 25% surface perforation, at a near-reattachment location (x/L = 0.73), is observed. However, the separation bubble in Mach 5.7 intake is suppressed most efficiently, when the cavity is covered with 17% porous surface. For Mach 7.9 intake also, the 25% surface perforation has maintained its superiority in reducing the wall static pressure to a maximum of 20.20% at x/L = 0.73. Once again, the 17% porous surface controlled configuration is found to be quite effective in suppressing the bubble. A qualitative investigation of the Schlieren images supports the findings of wall static pressure data.
Synthesis and Thermoelectric Properties of the B-Site Substituted SrTiO<sub>3</sub> with Vanadium
Khan, Tamal Tahsin,Mahmud, Iqbal,Ur, Soon-Chul Materials Research Society of Korea 2017 한국재료학회지 Vol.27 No.8
V-substituted $SrTiO_3$ thermoelectric oxide materials were fabricated by the conventional solid state reaction method. From X-ray diffraction pattern analysis, it can be clearly seen that almost every vanadium atom incorporated into the $SrTiO_3$ provided charge carriers. The electrical conductivity ${\sigma}$, Seebeck coefficient S, and thermal conductivity k were investigated in a high temperature regime above 1000 K. The addition of vanadium significantly reduced the thermal conductivity and enhanced the Seebeck coefficient, as well as the electrical conductivity, thus enhancing the ZT value. A maximum ZT value of 0.084 at 673 K was observed for the sample with 1.0 mole% of vanadium substitution. In this study, the reason for the enhanced thermoelectric properties via vanadium addition was also investigated.
Exploring drainage/relief-scape sub-units in Atreyee river basin of India and Bangladesh
Swades Pal,Tamal Kanti Saha 대한공간정보학회 2017 Spatial Information Research Vol.25 No.5
The prime objective of this study is to identify drainage and relief diversity models of the Atreyee river basin of India and Bangladesh for showing some relief and drainage sub units with unique characters. To achieve the goals, 20 associated morphometric parameters (e.g. drainage density, drainage frequency, relative relief, ruggedness number, slope, hydraulic gradient, dissection index etc.) have been used as spatial raster data layers. Weighted compositing method is applied for computing these models. Diversity models are classified for achieving the subcategories of the relief and drainage and each sub category possesses homogenous morphometric features. The high drainage diversity is found in the northern and middle western part especially along the Atreyee river and few patches of the alluvial tract. Although out of the total area only 8.98% area (1982.03 km2) falls under the very high diversity zone and in this area drainage density, frequency, texture etc. are also high. The high relief diversity zone (1.54%) displayed at the source and some middle western part of the basin. These models are also validated using some individual parameters using spatial correlation methods. High correlations significant at 95–99% level satisfy the sensitivity of Drainage and Relief diversity models.