Towards viable flow simulations of small-scale rotors and blade segments

The paper focuses on the possibilities of adequately simulating complex flow fields that appear around small-scale propellers of multicopter aircraft. Such unmanned air vehicles (UAVs) are steadily gaining popularity for their diverse applications (surveillance, communication, deliveries, etc.) and the need for a viable (i.e. usable, satisfactory, practical) computational tool is also surging. From an engineering standpoint, it is important to obtain sufficiently accurate predictions of flow field variables in a reasonable amount of time so that the design process can be fast and efficient, in particular the subsequent structural and flight mechanics analyses. That is why more or less standard fluid flow models, e.g. Reynolds-averaged Navier—Stokes (RANS) equations solved by the finite volume method (FVM), are constantly being employed and validated. On the other hand, special attention must be given to various flow peculiarities occurring around the blade segments shaped like airfoils since these flows are characterized by small chords (length-scales), low speeds and, therefore, low Reynolds numbers (Re) and pronounced viscous effects. The investigated low-Re flows include both transitional and turbulent zones, laminar separation bubbles (LSBs), flow separation, as well as rotating wakes, which require somewhat specific approaches to flow modeling (advanced turbulence models, fine spatial and temporal scales, etc). Here, the conducted computations (around stationary blade segments as well as rotating rotors), closed by different turbulence models, are presented and explained. Various qualitative and quantitative results are provided, compared and discussed. The main possibilities and obstacles of each computational approach are mentioned. Where possible, numerical results are validated against experimental data. The correspondence between the two sets of results can be considered satisfactory (relative differences for the thrust coefficient amount to 15%, while they are even lower for the torque coefficient). It can be concluded that the choice of turbulence modeling (and/or resolving) greatly affects the final output, even in design operating conditions (at medium angles-of-attack where laminar, attached flow dominates). Distinctive flow phenomena still exist, and in order to be adequately simulated, a comprehensive modeling approach should be adopted

Towards viable flow simulations of small-scale rotors and blade segments

The paper focuses on the possibilities of adequately simulating complex flow fields that appear around small-scale propellers of multicopter aircraft. Such unmanned air vehicles (UAVs) are steadily gaining popularity for their diverse applications (surveillance, communication, deliveries, etc.) and the need for a viable (i.e. usable, satisfactory, practical) computational tool is also surging. From an engineering standpoint, it is important to obtain sufficiently accurate predictions of flow field variables in a reasonable amount of time so that the design process can be fast and efficient, in particular the subsequent structural and flight mechanics analyses. That is why more or less standard fluid flow models, e.g. Reynolds-averaged Navier—Stokes (RANS) equations solved by the finite volume method (FVM), are constantly being employed and validated. On the other hand, special attention must be given to various flow peculiarities occurring around the blade segments shaped like airfoils since these flows are characterized by small chords (length-scales), low speeds and, therefore, low Reynolds numbers (Re) and pronounced viscous effects. The investigated low-Re flows include both transitional and turbulent zones, laminar separation bubbles (LSBs), flow separation, as well as rotating wakes, which require somewhat specific approaches to flow modeling (advanced turbulence models, fine spatial and temporal scales, etc). Here, the conducted computations (around stationary blade segments as well as rotating rotors), closed by different turbulence models, are presented and explained. Various qualitative and quantitative results are provided, compared and discussed. The main possibilities and obstacles of each computational approach are mentioned. Where possible, numerical results are validated against experimental data. The correspondence between the two sets of results can be considered satisfactory (relative differences for the thrust coefficient amount to 15%, while they are even lower for the torque coefficient). It can be concluded that the choice of turbulence modeling (and/or resolving) greatly affects the final output, even in design operating conditions (at medium angles-of-attack where laminar, attached flow dominates). Distinctive flow phenomena still exist, and in order to be adequately simulated, a comprehensive modeling approach should be adopted

Impact of cutting elements on forces and roughness of surface during turning hard steel X160 CrMo V12 with CBN tool

Cilj ovih istraživanja se odnosi na istraživanje uticaja elemenata režima rezanja na promenu sila rezanja, kvaliteta obrađene površine i promene fizičko-mehaničkih svojstava u površinskom sloju alata od CBN pri struganju čelika X160 CrMo V12, tvrdoće 60 ± 2 HRC. Rezultati istraživanja habanja površine alata ukazuju na prisustvo procesa oksidacije i promene fizičko-mehaničkih svojstava u površinskom sloju alata. Evaluacija sile jasno pokazuje da je radijalna sila (Fr) dominantna pri obradi ovog čelika. Razvijeni su matematički modeli zavisnosti sila rezanja i kvaliteta obrađene površine. Utvrđeno je da oksidacija površine alata, neposredno uz kontaktnu zonu alat-strugotina, dovodi do povećanja njihove tvrdoće i smanjenja čvrstoće, što u krajnjoj meri dovodi do pojave mikrokrzanja reznog sečiva a time i ubrzanog habanja alata.The goal of these researches is related to the analyses of the impact of elements of cutting mode on the change of cutting forces, quality of a machined surface and change of physical and mechanical properties of a surface layer of a CBN tool for turning of X160 CrMo V12 steel having a hardness of 60 ± 2 HRC. The results of the analyses of tool surface wear indicate the presence of oxidation and changes of physical and mechanical properties in a tool surface layer. The evaluation clearly shows that a radial force (Fr) is dominant during the machining of this steel. The mathematical models of dependence of cutting force and a quality of machined surface were developed. It was ascertained that an oxidation of the tool surface, next to a contact zone tool-cutting chip, leads to the increase of their hardness and reduction of their strength, and it finally leads to the emergence of micro-wear of a cutting knife and rapid tool wear

Cadmium toxicity in the epithelium of the initial epididymis segment after nicotine pretreatment

Određivan je učinak prethodne primjene nikotina na :ispoljavanje toksičnosti jednokratne visoke doze kadmijurna na epitel inicijalnog segmenta epididimisa pacova. Davanje nikotina je trajalo šest dana. Prva tri dana eksperimentalne životinje su dobijale i.p. po 1 mg/kg tjelesne težine vodenu otopinu nikotina a druga tri dana po 2 mg/kg težine. Šestog dana sa nikotinom je injicirano 4,58 mg/kg tjelesne težine kadmijuma. Kontrolne životinje su u istom periodu i. na isti način dobijale fiziološku otopinu. Životinje su žrtvovane dekapitacijorn dvanaest dana od posljednje injekcije. Sa histoloških preparata planimetrijski je određena površina koja pripada epitelu, intensticiju i lumenima presjeka ispitivanog segmenta epididimisa kao i zapremina jedara glavnih ćelija epitela. Histološkom analizom konstatovana je snažna vakuolizacija citoplazme glavnih ćelija i skraćenje stereocilija a statističkom obradom brojčanih podataka signifikantno smanjenje volumena jedara glavnih ćelija i površine epitela u odnosu na kontrolne životinje. Dobijeni rezultati su uspoređeni sa onim utvrđenim u identičnim eksperimentalnim uslovima nakon primjene samo nikotina odnosno samo kadmijuma.The paper deals with the effects of nicotine pretreatment on the occurrence of degenerative changes in the epithelium of the initial epididymis segment resulting from a single administration of a high cadmium dose. The nicotine pretreatment lasted six days. During the first three days the experimental animals were administered i.p. 1 mg/kg of nicotine water solution each, and during the following three days a dose of 2 mg/kg body weight. On the sixth day they received an injection of 4.58 mg/kg body weight of cadmium with nicotine. During the same period the control animals were given a physiological solution in the same manner. The animals were killed by decapitation twelve days after final injection. The histological sections were used for a planimetric determination of the surface areas belonging to the epitheliurn, .interstitium and Iumen of the epididymal duct and for volumetric analysis of the principal epithelial cell nuclei. Histological analysis showed prominent vacuolization of the principal cell cytoplasm, shortened stereociliae, a significantly decreased surface area belonging to the epithelium as well as a decrease in the principal cell nuclei volume as compared with control animals. The results were compared with those obtained in another experiment under identical experimental conditions following administration only of nicotine or cadmium

Genotypic differentiation of Monilinia spp. populations in Serbia using a high-resolution melting (HRM) analysis

Monilinia laxa, Monilinia fructicola and Monilinia fructigena are the three main causal agents of brown rot, which is one of the most important diseases of stone fruits in pre-and postharvest conditions. Nowadays, the need for the precise genotyping of these Monilinia species in terms of the genetic diversity of their populations or differences in their pathogenicity and host range is a prerequisite for any efficient disease management. In our study, the genetic structure of Monilinia populations in Serbia from three geographically distinct regions was investigated employing a high-resolution melting (HRM) analysis which is a sensitive and rapid molecular approach in fungal genotyping and diagnostics. Using species-specific primer pairs genotype-specific HRM melting curve profiles were generated allowing to efficiently decipher the genetic diversity of the Monilinia populations. The Monilinia genotypes could be easily distin-guished according to their melting curves. The isolates from the northern region were assigned to distinct genotypes and grouped rather independently compared to the isolates of the other two regions among all three tested Monilinia spp. M. fructicola and M. fructigena showed a higher genetic diversity among their populations (44%) compared with the genetic diversity among the M. laxa populations (7%). In contrast, the genetic variance within the pathogen populations was higher in the case of M. laxa (93%). Our data revealed an absence of host specificity in the Monilinia spp. populations. © 2020, Czech Academy of Agricultural Sciences. All rights reserved

Toxicity of copper hydroxide, dithianon, fluazinam, tebuconazole and pyraclostrobin to Didymella applanata isolates from Serbia

A study of the in vitro sensitivity of 10 isolates of Didymella applanata to copper hydroxide, dithianon, fluazinam, tebuconazole and pyraclostrobin, was conducted. The isolates were derived from diseased raspberry canes sampled during 2013 at five localities in western part of Serbia, known as the main raspberry growing region of the country. Prior to sensitivity testing experimental conditions for radial growth assay were optimized. The results showed that the temperature of 22 degrees C, oatmeal agar medium and 12/12 hrs light/ darkness light regimen provided the best conditions for sensitivity tests. Most of D. applanata isolates were sensitive to the tested fungicides. The narrowest range of EC50 values was recorded for tebuconazole (1.42-2.66mg L-1). The widest range of EC50 values was obtained for pyraclostrobin, ranging from 0.17mg L-1 to 55.33mg L-1. The EC50 values for the studied isolates were 39.48-51.19mg L-1 for copper hydroxide, 12.12-18.73mg L-1 for dithianon and 5.72-42.56mg L-1 for fluazinam. According to resistance factor values, all D. applanata isolates were sensitive to copper hydroxide, dithianon and tebuconazole. Among tested isolates, six were highly resistant to pyraclostrobin (RFs in the range of 207.1-325.5) and two moderately resistant to fluazinam (RFs were 3 and 7.4), respectively