二维圆柱在高超声速气流中的耦合传热计算

高超声速飞行器热结构和热防护设计离不开对飞行器表面的气动热载荷和固体内温度的准确预测,两者之间的耦合作用对此有着重要影响。开展高超声速流场与结构温度场的耦合数值计算,流场部分求解了二维非定常全N-S方程,空间差分采用Harten-Yee的TVD格式,时间离散采用双时间步推进。固体结构传热部分求解了二维非稳态的热传导方程。通过流固交界面,流体从固体部分得到温度边界条件,固体从流体部分得到热流边界条件,从而实现流场和固体温度场的紧耦合计算。将这套算法成功应用于绕无限长圆柱的气动加热计算中,对圆柱在气动加热过程中的温度变化做了详细的分析。

Numerical investigation of laminar heat transfer and nanofluid flow between two porous horizontal concentric cylinders

In this study, the laminar heat transfer and nanofluid flow between two porous horizontal concentric cylinders was investigated. The problem is investigated in two different geometries and the Re=10, 25, 50, 75, 100 and volume fraction 0, 0.2%, 0.5%, 2% and 5% that related to copper nanoparticles, and porous medium porosity of 0.5 and 0.9. Compared to the first geometry, the convective coefficient in the second geometry increases by 8.3%, 7% and 5.5% at Reynolds numbers of 100, 75 and 50, respectively. Comparison of the outlet temperatures for two heat fluxes of 300 and 1200 W/m^2 indicates a 2.5% temperature growth by a fourfold increase in the heat fluxes. Also, the higher Nusselt number is associated with the second geometry occurring at porosities of 0.9 and 0.5, respectively. In both geometries, the Nusselt number values at the porosity of 0.9 are higher, which is due to the increased nanofluid convection at higher porosities. The velocity of the nanofluid experiences a two-fold increase at the outlet compared to its inlet velocity in the first geometry and for both porosities. Similarly, a three-fold increase was achieved in the second geometry and for both porosities.

Convective Heat Transfer Characteristics of the Elliptic Cylinder with Axis Ratio 4∶1 in Crossflow

The heat transfer features around the elliptic cylinder of axis ratio 4∶1 in crossflow were investigated experimentally within a wide range of Reynolds number. By means of heat-mass transfer analogy and the naphthalene sublimation technique, the local heat transfer distribution and the mean heat transfer coefficient are clarified. The result shows that the mean heat transfer coefficient is higher than that of a circular cylinder in most Reynolds number range regarded, and this superiority turns to be more significant with the increase of flow speed. Moreover, the effect of axis ratio on mean heat transfer coefficient was investigated tentatively. The oil-lampblack technique was employed to enable visualization of the flow pattern around the cylinder and on the cylinder wall.

Ballistic thermal transport in a cylindrical quantum structure modulated with double quantum dots

Ballistic thermal transport properties in a cylindrical quantum structure modulated with double quantum dots(DQDs) are investigated.Results show that the transmission coefficients exhibit the irregular oscillation.Some resonant transmission peaks and stop-frequency gaps can be observed,and the number and positions of these peaks and gaps are sensitive to the sizes of DQDs.With increasing the temperature,the thermal conductance undergoes a transition from the decrease to increase,and can be efficiently tuned by modulating the radius,length of DQDs as well as the interval between DQDs.In addition,at low temperatures,the enhancement of the thermal conductance can be also observed in this case.Some similarities and differences between the cylindrical and rectangular structures are identified.

Numerical Simulation of Flow and Heat Transfer from Slot Jets Impinging on a Cylindrical Convex Surface

Flow and heat transfer characteristics of slot jets impingement to a cylindrical convex surface are numerically investigated.Suitable turbulence models have been determined through comparison with the experimental data.Flow structures are described and impingement heat transfer characteristics are discussed.The effects of Re,H/B and D/B on single-slot jets impingement heat transfer are analyzed and heat transfer characteristics of multiple-slot jets are investigated.The results show that:Gas flows along the convex surface and boundary layer separation occurs in both single and multiple-slot jets impingement.A maximum stagnation Nu appears at H/B=8 and the local Nu decreases with increasing H/B in the region far away from the stagnation.The Nu in the stagnation region decreases with increasing D/B but the Nu is nearly the same in the region far away from the stagnation.Pressure gradient is an important factor on heat transfer enhancement.Correlations of the Num for single-slot,double-slot and quadric-slot jets impinging on a convex surface are obtained.It indicates the effects of Re and D/B on Num could become more important in less slot jets impingement.

The numerical investigation of flow and heat transfer characteristics of flow past a slit-cylinder

The flow and heat transfer characteristics, including transition critical Reynolds number from two-dimensional to three-dimensional, the influence of slit-cylinder geometric parameter on Strouhal number, Nusselt number and forces acting on the slit-cylinder are numerically investigated. It's found that transition critical Reynolds number from two-dimensional(flow wake deforms in two directions) to three-dimensional(flow wake deforms in three directions) increases with the augment of the slit width ratio in the range of present considered Reynolds number. The present results indicate that the three-dimensional vortex structures resulting from the deformation of the vortex shedding have significant effects on flow and heat transfer features such as Strouhal number, Nusselt number and forces acting on the cylinders with different ratios of slit width. It's observed that the drag and lift coefficients reduce as the increase of slit width ratio, and vortex shedding is effectively suppressed by the slits.Moreover, the comprehensive heat transfer performance of the cylinder with the slits is significantly improved with the increase of the slit width ratio.