Surface correlations of hydrodynamic drag for transitionally rough engineering surfaces

Rough surfaces are usually characterised by a single equivalent sand-grain roughness height scale that typically needs to be determined from laboratory experiments. Recently, this method has been complemented by a direct numerical simulation approach, whereby representative surfaces can be scanned and the roughness effects computed over a range of Reynolds number. This development raises the prospect over the coming years of having enough data for different types of rough surfaces to be able to relate surface characteristics to roughness effects, such as the roughness function that quantifies the downward displacement of the logarithmic law of the wall. In the present contribution, we use simulation data for 17 irregular surfaces at the same friction Reynolds number, for which they are in the transitionally rough regime. All surfaces are scaled to the same physical roughness height. Mean streamwise velocity profiles show a wide range of roughness function values, while the velocity defect profiles show a good collapse. Profile peaks of the turbulent kinetic energy also vary depending on the surface. We then consider which surface properties are important and how new properties can be incorporated into an empirical model, the accuracy of which can then be tested. Optimised models with several roughness parameters are systematically developed for the roughness function and profile peak turbulent kinetic energy. In determining the roughness function, besides the known parameters of solidity (or frontal area ratio) and skewness, it is shown that the streamwise correlation length and the root-mean-square roughness height are also significant. The peak turbulent kinetic energy is determined by the skewness and root-mean-square roughness height, along with the mean forward-facing surface angle and spanwise effective slope. The results suggest feasibility of relating rough-wall flow properties (throughout the range from hydrodynamically smooth to fully rough) to surface parameters

Turbulent Fluid Flow Over Aerodynamically Rough Surfaces Using Direct Numerical Simulations

Incompressible turbulent fluid flow in aerodynamically rough channels is investigated using direct numerical simulations. A comprehensive database of simulation data for rough surfaces with different topographical properties has been developed for 17 industrially relevant rough surface samples. It includes numerous commonlyseen industrial rough surfaces such as concrete, graphite, carbon-carbon composite and ground, shotblasted and spark-eroded steel. Other surfaces such as cast, filed and gritblasted steel are also studied, along with replicas of ship propeller surfaces eroded by periods of service. The Reynolds number considered is Reτ = 180, for which the flow is in the transitionally rough regime. A study with variable δ/Sq ratio while keeping S + q constant, where Sq is the root mean squared roughness height, is conducted for one of the samples with the mean profiles showing convergence for δ/Sq >≈ 25. A Reynolds number dependence study is conducted for two of the samples with Reτ up to 720 showing a more complete range up to the fully rough flow regime, allowing the equivalent sandgrain roughness height, ks to be computed. A correlation based on the frontal and wetted roughness area is found to be superior to the surface skewness in predicting ∆U + based on the topographic surface parameters

Ozone (O3): an excellent adjunctive tool in medical and surgical management of patient

In the condition like increasing susceptibility to allergic reaction & weaken response to antibiotics, along with constantly growing prices for medical treatment, new non-medicinal methods are to be appreciated. The history of medical ozone starts in the XX century. The pioneers to apply ozone in clinical practice were E. Payer, A. Fish and H. Wolf. Ozone as an antiseptic means had been known and used from the beginning of the XX century, however, extensive and systemic research in the field of ozone therapy started in Germany in mid 70s, when ozone-resistant polymer materials and convenient ozone generating equipment came into every day clinical practice. Ozone (O3) therapy due to its disinfection effect & its capacity to transport & release oxygen into tissues is gaining a justified recognizing in many countries of the world. O3 therapy can produce its immune modulators, anti-inflammatory, bactericidal, virucidal, fungicidal, analgesics & other effects. Considering this the purpose of this literature is to highlight the significance of Ozone as an excellent adjunctive tool in the management of various medical and surgical conditions

Choosing a density functional for static molecular polarizabilities

Coupled-cluster calculations of static electronic dipole polarizabilities for 145 organic molecules are performed to create a reference data set. The molecules are composed from carbon, hydrogen, nitrogen, oxygen, fluorine, sulfur, chlorine, and bromine atoms. They range in size from triatomics to 14 atoms. The Hartree-Fock and 2nd-order M{\o}ller-Plesset methods and 34 density functionals, including local functionals, global hybrid functionals, and range-separated functionals of the long-range-corrected and screened-exchange varieties, are tested against this data set. On the basis of the test results, detailed recommendations are made for selecting density functionals for polarizability computations on relatively small organic molecules