Thermophysics and Aeromechanics最新文献

The results of experimental and computational studies of the processes of hydrodynamics and heat transfer of a swirling flow, heated by the counter coolant flow in the heat exchange channel under standard technological parameters of a nuclear power plant are presented in this paper. The temperature field of the heat exchange channel as a whole and the coefficient of hydraulic resistance of channels with twisted tapes of a constant swirl pitch were obtained in experiments.

The numerical study was carried out using the domestic software package LOGOS and the Ansys CFX complex. The simulations were performed using the k-ω SST turbulence model, corrected for streamline curvature and rotation. Two versions of the calculation grid were developed. A comparative analysis of the calculated and experimental values of the hydraulic friction coefficient, the swirling flow temperature, and the heat transfer coefficients from the wall to the swirling flow was carried out. The analysis allowed identification of the strengths and weaknesses of the calculation methodology implemented in the domestic package. Deviations of the obtained values were compared. There is a good agreement between the calculated and experimental data, as well as with the data based on generalized dependences. One of the most important conclusions of the study is the need to modernize the process of solving the coupled heat transfer problem in the LOGOS package to expand the range of problems to be solved.

The study is aimed at measuring the gas flow temperature by thermocouples whose time of reaching the equilibrium temperature is comparable with the measurement time, and heat release to structural elements of the transducer can be rather large. The results of numerical simulations of the gas flow in the temperature transducer used for measuring the stagnation temperature in high-enthalpy hotshot wind tunnels are presented. A coupled problem of the air flow around the temperature transducer is solved, and the flow field inside the stagnation chamber is calculated with allowance for heat losses to input wires and structural elements of the transducer. The data obtained are considered as the results of a virtual experiment and are treated by methods of experimental aerodynamics. The retrieved results are compared with the initial numerical values of the stagnation temperature in the flow impinging onto the transducer. The sources of uncertainties arising in temperature measurements are determined, and the applicability of experimental methods for determining the stagnation temperature in short-duration wind tunnels, including those with parameters decreasing during the run, is justified.

It is shown that the method of “two thermocouples” can be successfully used to determine the stagnation temperature even if the heat losses to transducer elements are comparable with heat input from the gas flow. The values of the retrieved stagnation temperature correspond to the flow temperature in the transducer within 1.2–3 % depending on the initial temperature of the thermocouple.

Numerical simulation of unsteady processes proceeding during the laser welding of plates made of porous and monolithic (non-porous) metals was carried out. The influence of the welding speed on the quality of resultant welded joints and seam morphology was studied. The calculated characteristics of connections between porous and monolithic stainless-steel plates are in qualitative agreement with the results of physical experiments.

The article considers the development of a near-wall separation vortex arising at a supersonic flow around the external dihedral corner due to the pressure drop between its faces, in the range of angles of attack α = 0.5°–6°. The processes of the origin and development of separation and secondary vortices at the angle increase are investigated in detail. Particular attention is paid to the flow structure change in the vortex location zone. A clear violation of the flow self-similarity in the front part of the model in the zone of vortex system formation is shown.

The effect of wall treatment on the performance of k-ε model in incompressible, turbulent, separated flows with and without heat transfer has been evaluated in this study. We have simulated two benchmark cases: (i) flow past a circular cylinder at Re = 3900, and (ii) flow past a heated square cylinder at Re = 21 400 using the open source CFD package: OpenFOAM. We have compared three variants of the k-ε model, namely, Launder-Sharma k-ε model (Yap corrected) (LSKEY), Lam–Bremhorst k-ε model (Yap corrected) (LBKEY) and two-layer k-ε model (TLKE) along with the available experimental and direct numerical simulation (DNS) data. Comparisons are made in terms of the models’ capability to predict the mean flow variables, surface integral quantities, and heat transfer characteristics at different wake locations. On the basis of the presented study, we conclude that LSKEY performs better than the other models in predicting the wake and surface flow and heat transfer parameters. Further our comparisons show that, while LSKEY and LBKEY require comparable clock time per flow-through cycle, the computational time needed by TLKE is almost twice as compared to LBKEY or LSKEY. These results call for more attention from the CFD community onto the LSKEY model, in particular, so that it can be incorporated in various other flow fields, especially the scale resolving methodologies like the partially-averaged Navier-Stokes (PANS) equations, wherein a superior wall treatment along with a shorter computational time could be of immense advantage. In authors’ opinion, these benefits of the LSKEY model have largely been overlooked, perhaps because of a biased preference to the TLKE model, which enjoys the default presence in popular commercial CFD packages.

The paper presents the results of experimental study of the solubility (VLE-properties) of crystalline tricosane in pure and modified supercritical carbon dioxide over the temperature range from (308.15 to 315.15) K and at the pressures from (8.00 to 20.32) MPa using the dynamic method. Modification of carbon dioxide fluid was performed by adding several organic solvents, such as dimethylsulfoxide, ethanol, acetone, and chloroform. It was found that using the fluid co-solvents at the concentration of 5 wt. % improves the tricosane solubility by a factor of two. The measurement results have been described by the Penga–Robinson equation of state.

Physicochemical and thermal processes occurring during methane conversion into synthesis gas under non-isothermal conditions in microstructural heat exchanger-reactors based on microchannels are considered in this paper. A method for synthesizing a rhodium-based composite thin-layer catalyst for steam reforming of methane and carbon monoxide is proposed, and the results of experimental and numerical studies of the features of steam reforming under controlled thermal conditions of a microchannel reactor are presented. The determining influence of thermal processes on the rate and sequence of multi-stage heterogeneous reactions has been revealed; the methods for controlling the steam reforming process have been developed to achieve high completeness of chemical transformations.

In this paper, a novel thermal lattice Boltzmann approach is proposed for the implementation of the thermal boundary conditions at the fluid-solid interface. The numerical code, developed on the basis of the new approach, was validated against reliable numerical data from the literature in the cases of both square and circular conducting blocks. Analytical and experimental validations were also performed in the case of a circular block. The numerical tests show that the adopted approach makes it possible to handle interface problems with large thermal conductivity ratios. In the present study, this approach is validated first in the case of a square conducting block and used to simulate a conjugate convection-conduction problem in a square cavity enclosing a circular block. The novel developed TLBM approach reduces computational memory as well as numerical programming issues associated with the use of a hybrid method that combines the lattice Boltzmann method and classical methods.

Results of numerical investigations of the characteristics of a turbulent boundary layer in the case of air blowing through a smooth flat perforated surface with a single hole and also through a similar surface with a group of staggered holes 0.18 mm in diameter (d/δ=0.0072) in a low-velocity flow are reported. The Reynolds number Re** based on the momentum thickness δ** ahead of the perforated region is 2600. The blowing coefficient C_b is varied in the interval from zero to 0.0438. The influence of some geometric parameters, in particular, the distance between the hole centers, on the properties of the transverse shear flow for identical intensities of blowing in situations with one hole and with a group of holes is analyzed. All observations reveal stable reduction of local friction whose value varies depending on the number of holes and their arrangement on the surface.

An experimental study of heat transfer and hydraulic losses in a channel with one wall being a surface with trench dimple was carried out. The working surface had four rows of dimples located alternately at angles of 45° and −45° to the channel axis. In the laminar regime, the transfer of heat and the losses of pressure turned out to be close to the parameters of a smooth channel. In the turbulent regime, a 1.5-fold enhancement of heat transfer with respect to the transfer of heat in a smooth channel was obtained. The dependence of the increase in pressure losses on the Reynolds number qualitatively agreeing with the dependence for the channels with sandy roughness is obtained.