Convection Velocity in Turbulent Boundary Layers under Adverse Pressure Gradient

The convection velocity ($U_C$) of turbulent structures has been studied in adverse-pressure-gradient (APG) turbulent boundary layers (TBLs) for a wide range of Reynolds numbers $Re_\tau = 1400 - 4000$. The study is based on estimation of the convection velocity using decomposed streamwise skewness factor introduced in (Drozdz A., Elsner W., Int. J. of Heat and Fluid Flow. 63 (2017) 67\-74) and verified by means of two-point correlation method. It was shown that in the overlapping region of APG flows, the convection velocity profiles (when scaled in viscous units) reassemble the universal logarithmic law characteristic for the ZPG flows up to Clauser-Rota pressure gradient parameter $\beta \lesssim 19$ for the considered range of Reynolds number, what means that in the inner region of TBL the friction velocity in APG is not proportional to $U$ (as in ZPG) but to $U_C$ instead. The physical mechanism that explains the impact of increased convection velocity on the mean flow is proposed. The difference between $U_C$ and $U$ increases as a function of APG, which causes the stronger sweeping that enhances momentum transfer to the wall and compensates the weaker mean shear profile that is created by lower vorticity near the wall. This effect is a result of an enhancement of amplitude modulation of the small scales by large scale motion. The process becomes more pronounced as eddy density grows, so with increasing Re. The proposed model addresses a number of literature observations found in adverse pressure gradient flows which have been so far left without a well-founded explanation.Comment: 25 pages, 11 figure

Numerical analysis of CO₂ capture efficiency in post combustion CCS technology in terms of varying flow conditions

The paper deals with the computational fluid dynamics modelling of carbon dioxide capture from flue gases in the post combustion-capture method, one of the available carbon capture and storage technologies. 30% aqueous monoethanolamine solution was used as a solvent in absorption process. The complex flow system including multiphase countercurrent streams with chemical reaction and heat transfer was considered to resolve the CO2 absorption. The simulation results have shown the realistic behaviour and good consistency with experimental data. The model was employed to analyse the influence of liquid to gas ratio on CO2 capture efficiency

CFD modelling of CO2 capture in a packed bed by chemical absorption

The paper deals with numerical modelling of carbon dioxide capture by amine solvent from flue gases in post-combustion technology. A complex flow system including a countercurrent two-phase flow in a porous region, chemical reaction and heat transfer is considered to resolve CO2 absorption. In order to approach the hydrodynamics of the process a two-fluid Eulerian model was applied. At the present stage of model development only the first part of the cycle, i.e. CO2 absorption was included. A series of parametric simulations has shown that carbon dioxide capture efficiency is mostly influenced by the ratio of liquid (aqueous amine solution) to gas (flue gases) mass fluxes. Good consistency of numerical results with experimental data acquired at a small-scale laboratory CO2 capture installation (at the Institute for Chemical Processing of Coal, Zabrze, Poland) has proved the reliability of the model

Power Plant Optimisation—Effective Use of the Nelder-Mead Approach

This paper demonstrates the use of a combined software package including IPSEpro and MATLAB in the optimisation of a modern thermal cycle. A 900 MW power plant unit (operating at ultra-supercritical conditions) was considered as the study object. The Nelder-Mead simplex-based, direct search method was used to increase power plant efficiency and to find the optimal thermal cycle configuration. As the literature reveals, the Nelder-Mead approach is very sensitive to the simplex size and to the choice of method coefficients, i.e., reflection, expansion and contraction. When these coefficients are improperly chosen, the finding of the optimal solution cannot be guaranteed, particularly in such complex systems as thermal cycles. Hence, the main goal of the present work was to demonstrate the capability of an integrated software package including IPSEpro, MATLAB and MS Excel in the optimisation process of a complex thermal cycle, as well as to examine the effectiveness of the most popular sets of Nelder-Mead coefficients previously proposed by other researchers. For the investigation purposes, the bleed and outlet pressures from the turbines were considered as decision variables, and the power plant efficiency was used as an objective function

The Analysis of Nitrogen Oxides Formation During Oxygen - Enriched Combustion of Natural Gas

This paper presents the study of oxygen–enriched combustion of natural gas and its impact on nitrogen oxides emission. The research were performed on two experimental stands, i.e. combustion chambers with an industrial swirl burner of maximum power equal to 90 kW and 10 kW. The investigation includes the influenced of oxygen enhanced within the range between 21% and 30%. Furthermore, the role of temperature during the oxygen enrichment was analysed. The results of the research showed that with the rise in oxygen concentration in the air the concentration of nitrogen oxides also increases what is directly related to the rise in flame temperature as well as the addition of oxygen

Utilization of Rayleigh waves for engine oil level measurements

The paper deals with the problematics of the measurement of engine oil level based on the correlation between the attenuation of the surface Rayleigh wave and the fluid level. Available literature offers a few methods, which utilizes the surface acoustic waves for such a purpose, leaving the problem not completely resolved. The theoretical assumptions regarding Rayleigh wave formation on the free surface were supported by numerical simulations in COMSOL Multiphysics software. The final part of this article describes an experimental device that has been designed and manufactured for the measurement purposes including the proposal of the measuring method based on the attenuation of Rayleigh surface waves under the influence of propagation along the solid-liquid interface.Web of Science138227527

Studies of acoustic wave propagation when facing obstacle

Control of flame behaviour has a number of practical applications. This task is not trivial and a rapidly growing body of research related to this subject can be recently observed. A promising solution for such a problem could be a technology utilising the acoustic waves. One may expect that the acoustic excitation characterised by the same pressure level will interact with the flame differently, when the environment configuration in flame's close vicinity changes. Hence the issue related to the propagation of the acoustic waves in the presence of obstacles is worth of interest. The paper presents results of studies taken on acoustic field propagation when the acoustic excitation is carried with and without acoustic screen.Web of Science138228228