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

The usage of 3D printing in the analysis of the product design: Case: Electronic enclosure of compact pressure transmitter

Aditivna proizvodnja uključuje izradu proizvoda složene geometrije u relativno malim količinama, kao i izradu alata i kalupa za masovnu proizvodnju. Aditivnom proizvodnjom realizuju se modeli prema digitalnom prikazu, a primena je ogromna u različitim industrijskim sektorima. U poređenju sa tradicionalnom proizvodnjom, glavni parametri u odabiru aditivne tehnologije su: ušteda energije, smanjenje otpada, smanjenje upotrebe većeg broja alata, kao i optimizacija dizajna. Aditivna proizvodnja ili tehnologija 3D štampe rade na principu dodavanja materijala u slojevima, tj. model se formira od slojeva rastopljenog materijala koji se odmah hladi i očvršćava. 3D štampa omogućava čestu i jednostavnu modifikaciju modela na zahtev kupca, a pre ulaska modela u samu proizvodnju. Ovo čini komunikaciju na relaciji proizvođač-kupac dosta jednostavnom. Polazni materijal za izradu modela je polilaktična kiselina (PLA). To je ekološki termoplastični poliester koji se prirodno razgrađuje u prirodi. Na mehaničke karakteristike realizovanog modela od PLA značajno utiču različite tehnološke promenljive kao što su: prečnik brizgaljke, debljina definisanog sloja, procentualna vrednost ispune, veličina uzorka koji se puni, brzina punjenja i temperatura proizvodnje. Cilj ovog rada je da se prikaže postupak realizacije kutije elektronike za malogabaritni transmiter pritiska na 3D štampaču. Time se projektantu daje mogućnost da ispravi postojeće greške, modifikuje proizvod prema zahtevima krajnjih korisnika i na kraju daje polazna osnova za realizaciju prototipa novog proizvoda.Additive manufacturing involves manufacturing of products with complex geometry in relatively small quantities, as well as the tools and molds manufacturing for mass production. With additive manufacturing, digital models are being realized and implementation is huge in various industrial sectors. Compared to traditional manufacturing, the main parameters in the choice of additive technology are: energy savings, waste reduction, reduced use of more tools and optimization of design. Additive manufacturing or 3D printing technology works on the principle of adding material in layers, i.e. the model is formed from layers of molten material that is immediately cooled and solidified. 3D printing allows to work with customers to solve design problems before embarking on a launch production. The starting material for the model is polyactic acid (PLA). It is an eco-friendly thermoplastic polyester, that breaks down naturally. The mechanical characteristics of the realized PLA model are significantly influenced by various technological variables, such as following: nozzle diameter, thickness of defined layer, percentage of fill, sample size to be filled, filling rate and production temperature. The aim of this paper is to present the process of realization of an electronics enclosure for a compact pressure transmitter on a 3D printer. This gives the designer the possibility to correct existing errors, modify the product according to the wishes of the end users and finally provides a starting point for the prototype of new product

The usage of 3D printing in the analysis of the product design: Case – Electronic enclosure of compact pressure transmitter

Aditivna proizvodnja uključuje izradu proizvoda složene geometrije u relativno malim količinama, kao i izradu alata i kalupa za masovnu proizvodnju. Aditivnom proizovnjom realizuju se modeli prema digitalnom prikazu, a primena je ogromna u različitim industrijskim sektorima. U poređenju sa tradicionalnom proizvodnjom, glavni parametri u odabiru aditivne tehnologije su: ušteda energije, smanjenje otpada, smanjenje upotrebe većeg broja alata, kao i optimizacija dizajna. Aditivna proizvodnja ili tehnologija 3D štampe rade na principu dodavanja materijala u slojevima, tj. model se formira od slojeva rastopljenog materijala koji se odmah hladi i očvršćava. 3D štampa omogućava čestu i jednostavnu modifikaciju modela na zahtev kupca, a pre ulaska modela u samu proizvodnju. Ovo čini komunikaciju na relaciji proizvođač-kupac dosta jednostavnom. Polazni materijal za izradu modela je polilaktična kiselina (PLA). To je ekološki termoplastični poliester koji se prirodno razgrađuje u prirodi. Na mehaničke karakteristike realizovanog modela od PLA značajno utiču različite tehnološke promenljive kao što su: prečnik brizgaljke, debljina definisanog sloja, procentualna vrednost ispune, veličina uzorka koji se puni, brzina punjenja i temperatura proizvodnje. Cilj ovog rada je da se prikaže postupak realizacije kutije elektronike za malogabaritni transmiter pritiska na 3D štampaču. Time se projektantu daje mogućnost da ispravi postojeće greške, modifikuje proizvod prema zahterima krajnjih korisnika i na kraju daje polazna osnova za realizaciju prototipa novog proizvoda.Additive manufacturing involves manufacturing of products with complex geometry in relatively small quantities, as well as the tools and molds manufacturing for mass production. With additive manufacturing, digital models are being realized and implementation is huge in various industrial sectors. Compared to traditional manufacturing, the main parameters in the choice of additive technology are: energy savings, waste reduction, reduced use of more tools and optimization of design. Additive manufacturing or 3D printing technology works on the principle of adding material in layers, i.e. the model is formed from layers of molten material that is immediately cooled and solidified. 3D printing allows to work with customers to solve design problems before embarking on a launch production. The starting material for the model is polyactic acid (PLA). It is an eco-friendly thermoplastic polyester, that breaks down naturally. The mechanical characteristics of the realized PLA model are significantly influenced by various technological variables, such as following: nozzle diameter, thickness of defined layer, percentage of fill, sample size to be filled, filling rate and production temperature. The aim of this paper is to present the process of realization of an electronics enclosure for a compact pressure transmitter on a 3D printer. This gives the designer the possibility to correct existing errors, modify the product according to the wishes of the end users and finally provides a starting point for the prototype of new product

Effectiveness of fungicides and an essential-oil-based product in the control of grey mould disease in raspberry

Field experiments were conducted in two commercial raspberry fields to evaluate effectiveness of some fungicides and an essential oil based product in the control of Botrytis fruit rot. The experiments consisted of four fungicides - fenhexamid, vinclozolin, benomyl, and pyrimethanil, two essential oil product treatments (0.5% and 1% emulsion) and untreated control, in randomized block design with four replicates per treatment. Afterwards, the pathogen was isolated from infected fruits and identified based on colonial and conidial morphology. Sensitivity of 10 randomly chosen isolates to all mentioned fungicides and tea tree oil was determined in radial growth assay on PDA supplemented with a range of concentrations of the relevant product. At both localities, the highest efficacy was achieved by pyrimethanil (97.4% and 98.2%) and fenhexamid (93.6% and 97.6%), while the efficacy of tea tree oil, applied at both concentrations, was less than satisfactory and ranged from 13.3% to 55.9% compared to the control. In vitro sensitivity of B. cinerea was determined based on EC-50 values which ranged between: 0.14 mg/l and 0.20 mg/l for vinclozolin, 0.16 mg/l and 0.46 mg/l for benomyl, 0.22 mg/l and 3.81 mg/l for pyrimethanil, 0.06 mg/l and 0.19 mg/l for fenhexamid, and 383.3 mg/l and 1500.6 mg/l for tea tree oil product

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