This article briefly reviews the recent works related to small-scale combustion and its potential impact into combustion science and engineering is presented. Followed by a simple description of the scale effect on combustion to highlight its “unique” feature, past related works are then summarized. The impact of heat recirculation appearing in combustion systems, which is the most prominent feature of a micro- or small-scale combustion system, is focused upon and is understood that exactly the same strategy promising better combustion performance is confirmed irrespective of flame type (either premixed or non-premixed). With respect to this, paying attention to the entire combustor design, to optimize within the target working range is a crucial matter when micro-scale combustion is adopted. Potential subjects to be covered to further promote these aspects in this field are then presented.
A finite volume based three dimensional numerical studies on the heat transfer due to natural convection inside the inclined cubical cavity filled with CNT-water nanofluid is solved by vorticity-vector potential formalism. The enclosure contains an Ahmed body at its middle with differentially heated vertical walls. The other walls are adiabatic. The effect due to Rayleigh number (103 ≤ Ra ≤ 105), volumetric fraction (0 ≤ φ ≤ 0.05) of CNT particles, angle of incidence of enclosure (0° ≤ γ ≤ 180°) and thermal conductivity ratio (0.01 ≤ Rc ≤ 100) are analyzed. The results of fluid flow with single phase model are elucidated with Particle trajectories, Velocity vectors, Iso-surfaces of temperature and Nusselt number. CNT-particles enhanced the heat transfer in all the considered cases. Maximum average Nusselt number is reported when the angle of inclination is 30° and 150°. The variation in thermal conductivity ratio has a least effect on convection.
The dissimilarity between the momentum and heat transfer due to streamwise traveling wave-like wall deformation in turbulent channel flows is investigated through direct numerical simulations. The flow rate is kept constant, and the bulk Reynolds number is Reb = 5600. A constant temperature difference condition is imposed on the channel walls. The parametric study shows that the heat transfer is enhanced when the wave travels in the upstream direction. The maximum analogy factor is found to be 1.13, i.e., 13% enhancement of heat transfer under a given pressure gradient, when the wall deformation amplitude is large and the wall deformation period is short. An analysis using the identity equations for the drag and the heat transfer with a three component decomposition reveals that the random component plays an important role in the enhancement of the heat transfer.
Three-dimensional numerical simulations are carried out to investigate the effects of film-hole arrangement and blowing ratio on the squealer tip leakage flow field and tip film-cooling performance. Six film-hole arrangements with 13 holes are designed in the current study for comparison. In type-A and type-B, the film-cooling holes are arranged in a single row, located at the middle camber line or close to the suction-side squealer. The four modified film-hole arrangements are realized by placing two rows of total 7 film-cooling holes at the leading edge (type-C, type-D, type-E and type-F) and remaining the rest film-cooling holes in a row at the middle chord zone. The results show that the leakage flow entering the tip gap from the leading edge of suction side, the leading edge of pressure side and the middle chord and trailing edge of pressure side behaves different flow feature inside the tip cavity, inducing complicated swirling flow filed. The modified film-hole arrangements yield more reasonable film coverage on the tip surface by comparing with the single row film-hole arrangement under relatively high blowing ratios. In addition, the modified film-hole arrangements also show different rules on the film-cooling effectiveness distributions over some specific surfaces, such as tip cavity bottom surface and squealer top surface, as well as PS squealer inner surface and SS squealer inner surface. Among the presented four modified film-hole arrangements, type-D and type-F gain the most favorable film-cooling improvement.
In the present work, the generalized thermoelastic interactions in a hollow cylinder with one relaxation time are considered. The modulus of elasticity are taking as function of temperature. Due to the nonlinearity of the governing equations, finite element method is adopted to solve such problem. The exact solution in the case of temperature-independent is discussed explicitly. Numerical results for the temperature distribution, displacement and radial and hoop stresses represented graphically. The accuracy of the finite element method validated by comparing between the finite element and exact solutions for temperature-independent.
A parametric investigation of secondary flow control using endwall vortex generator jet (VGJ) is performed in a high turning compressor cascade. The mechanisms for the variations of VGJ performance with different jet parameters including the pitch angle, yaw angle and jet-to-inflow total pressure ratio are discussed in detail. And then the potential of VGJ at the off-design points is further validated. The results show that the influence of VGJ on the cascade performance depends on the combination of the loss increase in the upwash region and the loss reduction in the corner region. A jet pointing upstream of the cascade or with too large jet-to-inflow total pressure ratio would enhance the mixing losses in the upwash region remarkably. Whereas a jet with negative yaw angle, too large or too small pitch angle would reduce the effects of VGJ on the endwall cross flow and the low energy fluid accumulation in the corner region due to the weakened reverse vortex. In this work, the optimal performance is obtained by the jet with a pitch angle of 20° and a yaw angle of 0°. For the off-design points, the potential of VGJ on the loss reduction is enhanced with the increase of the incidence. The loss reductions at i=-5° and i=5° are 13.2% and 32.5% respectively, whereas the beneficial effect on the flow turning decreases slightly.
Edited and published by : The Japan Society of Mechanical Engineers and The Heat Transfer Society of Japan Produced and listed by : Showa Joho Process Co., Ltd.(Vol.8 No.3-) Sanbi Printing Co., Ltd.(Vol.1 No.1-Vol.8 No.2)