Computational Study on Radiative Aerothermodynamics of a Reentry Space Vehicle

Under hypersonic flight conditions, a vehicle travelling through the atmosphere could excite the air that flows around the body to very high temperatures as the kinetic energy of the vehicle is dissipated to the gas. Depending on the flight velocity, various chemical reactions will be produced behind a shock wave for stagnation region. These reactions greatly change the properties of air and cause considerable deviation from those of a thermally and calorically perfect gas. A vehicle flying through the higher altitude of the atmosphere at high velocities may also experience thermal non-equilibrium since the lower density reduces the collision frequency and the high velocity results in smaller transit times for the air molecules. Under such extremely thermal circumstances, the heat transfer by convection and radiation around a vehicle has been one of key issues for thermal protection system (TPS). In this paper, the computational aerothermodynamics with fully coupled radiative heat transfer is developed. To validate the proposed approach, it is employed to simulate the thermal and chemical nonequilibrium flows over Stardust. The computed results on the reentry space vehicle reveal both of convective flux and radiative flux are in good agreements with other predicted results.

A theory of glacial cycles: resolving Pleistocene puzzles

Since the summer surface air temperature that regulates the ice margin is anchored on the sea surface temperature, we posit that the climate system constitutes the intermediary of the orbital forcing of the glacial cycles. As such, the relevant forcing is the annual solar flux absorbed by the ocean, which naturally filters out the precession effect in early Pleistocene but mimics the Milankovitch insolation in late Pleistocene. For a coupled climate system that is inherent turbulent, we show that the ocean may be bistable with a cold state defined by the freezing point subpolar water, which would translate to ice bistates between a polar ice cap and an ice sheet extending to mid-latitudes, enabling large ice-volume signal regardless the forcing amplitude so long as the bistable thresholds are crossed. Such thresholds are set by the global convective flux, which would be lowered during the Pleistocene cooling, whose interplay with the ice-albedo feedback leads to transitions of the ice signal from that dominated by obliquity to the emerging precession cycles to the ice-age cycles paced by eccentricity. Through a single dynamical framework, the theory thus may resolve many long-standing puzzles of the glacial cycles.

Study of Prepared α-Chymotrypsin as Enzyme Nanoparticles and of Biocatalytic Membrane Reactor

Biocatalytic kinetic effect of α-chymotrypsin enzyme has been investigated in its free and pretreated forms (it was covered by a very thin, porous polymer layer, called enzyme nanoparticle) as well as its immobilized form into pores of polysulfone/polyamide asymmetric, hydrophilic membrane. Trimethoxysilyl and acrylamide-bisacrylamide polymers have been used for synthesis of enzyme nanoparticles. Applying Michaelis-Menten kinetics, the KM and vmax values of enzyme-polyacrylamide nanoparticles are about the same, as that of free enzyme. On the other hand, enzyme nanoparticles retain their activity 20–80 fold longer time period than that of the free enzyme, but their initial activity values are reduced to 13–55% of those of free enzymes, at 37 °C. Enzyme immobilized into asymmetric porous membrane layer remained active about 2.3-fold longer time period than that of native enzyme (at pH = 7.4 and at 23 °C), while its reaction rate was about 8-fold higher than that of free enzyme, measured in mixed tank reactor. The conversion degree of substrate was gradually decreased in presence of increasing convective flux of the inlet fluid phase. Biocatalytic membrane reactor has transformed 2.5 times more amount of substrate than the same amount of enzyme nanoparticles and 19 times more amount of substrate than free enzyme, measured in mixed tank reactor.

Tidally induced stellar oscillations: converting modelled oscillations excited by hot Jupiters into observables

ABSTRACT We calculate the conversion from non-adiabatic, non-radial oscillations tidally induced by a hot Jupiter on a star to observable spectroscopic and photometric signals. Models with both frozen convection and an approximation for a perturbation to the convective flux are discussed. Observables are calculated for some real planetary systems to give specific predictions. The photometric signal is predicted to be proportional to the inverse square of the orbital period, P−2, as in the equilibrium tide approximation. However, the radial velocity signal is predicted to be proportional to P−1, and is therefore much larger at long orbital periods than the signal corresponding to the equilibrium tide approximation, which is proportional to P−3. The prospects for detecting these oscillations and the implications for the detection and characterization of planets are discussed.

Numerical Analysis of Turbulent Flow over a 2-D Prolate Spheroid

Recently external flow over body creates more interest of study because flow characteristics are dominated by complex phenomenon like separation and transition.in this paper turbulent flow over a 2-D prolate spheroid (6:1) is consider for analysis. Generation of surface grid around prolate spheroid by using grid generation code MESHGEN. Laminar and turbulent Flow past given geometry is simulated by Navier-stoke code RANS3D by second order upwind scheme for convective flux discretization by k-ε model for different Reynolds number, angles of attack .It is observed that the value of drag coefficient is lower than that of a cylinder due to its more streamlined contour. The variation of Cd was steeper in the laminar range than the turbulent range due to the effects of viscous forces being greater in laminar flow.

A short review on porous media convection

We briefly review the investigations of pattern formation and transport properties of Rayleigh-Darcy convection (or the Elder Problem), including laboratory experiments, theoretical analysis and numerical simulations. It is shown that the flow exhibits power-law-scaling characteristics at large Rayleigh-Darcy number $Ra$, a dimensionless parameter representing the ratio of the driving buoyancy forces to the diffusive forces. Namely, the mean spacing between neighboring interior plumes shrinks as $Ra^{-\alpha}$ with the scaling exponent $\alpha \le 1/2$ and the convective flux increases linearly with $Ra$. However, more laboratory experiments are needed to validate these scalings. Additionally, many conditions, e.g. the inclination of the layer and hydrodynamic dispersion, etc., may lead to a large uncertainty in the flow pattern and transport efficiency.

Performance comparison between an improved and a classical Trombe wall: An experimental study

In this article, the comparison of energy performance between a classical and an improved Trombe wall of a model test room has been carried out experimentally. The case study is conducted in Borj Cedria, Tunisia, where there is always heating requirements. Here, we propose an improved Trombe wall whose absorber wall is covered with a thin black copper panel backed rather than simply painted black wall. The proposed idea would offer improved thermal performance, especially in natural convection. The comparison shows that the improved Trombe wall design gives an increase for both conductive and convective flux. The results show that the improved Trombe wall works more effectively than the classical Trombe wall system in utilizing solar energy for the example of test room.