Aerodynamic analysis of a light aircraft at different design stages

Tokom aerodinamičkog projektovanja aviona, shodno njegovoj kategoriji i fazi razvoja projekta, potrebno je koristiti adekvatne proračunske metode i softverske alate. U slučaju lakih aviona, uobičajeno se koriste analitičke i semiempirijske metode u inicijalnoj fazi, kombinovane sa jednostavnim - neviskoznim CFD proračunskim modelima, dok se u kasnijim fazama obavljaju relativno kompleksne CFD analize sa uticajem viskoznosti. U današnje vreme se, u kategoriji lakih aviona, podrazumeva da savremeni proračunski alati za svaku od faza razvoja moraju biti adekvatno izabrani, tako da se njima dobijeni rezultati međusobno verifikuju i dopunjavaju. U radu su prikazane proračunske metode korišćene tokom aerodinamičke analize novog lakog aviona u različitim fazama njegovog razvoja i izvršeno je poređenje dobijenih rezultata, u cilju verifikacije ispunjenja navedenog uslova.During the evolution of an airplane aerodynamic design, proper calculation methods and software tools should be utilized, which correspond to the airplane category and project development level. In case of light aircraft, the general trend is the application of analytical and semiempirical methods at the initial stages, combined with simplified - inviscid CFD computational models, and fairly complex viscous CFD analyses at higher design levels. At the present stage of light aviation development, it is assumed that the contemporary design tools for each of those steps should be appropriate enough, so that they actually verify and additionally fine-tune each other's results. This paper describes the calculation tools and methods applied during the aerodynamic analyses of a new light aircraft at different development stages, and compares the results obtained by them, with the aim to verify and support the above statement, considering light aircraft aerodynamic design

Numerical modelling of velocity profile parameters of the atmospheric boundary layer simulated in wind tunnels

Experimental and numerical modeling and simulations of the wind influence within the atmospheric boundary layer are essential tools in optimum building structural design. Each of these methods, however, has both advantages and disadvantages. In experimental investigations performed in wind tunnels, reliable results can be obtained, but detailed information of the wind profile parameters, such as the surface roughness length z 0 or the friction velocity u∗, are difficult to determine. Numerical simulations, on other hand, easily yield any information of the wind velocity profile. However, the reliability of numerical results strongly depends on the established and adopted computational model. This paper presents the computational fluid dynamics (CFD) analysis of the atmospheric boundary layer simulated in subsonic wind tunnels using appropriate types of obstacles, based on the SST k-ω turbulence model with optimized unstructured mesh and optimum selection of relevant physical model parameters, performed in Ansys Fluent software. Results have been compared with the measurements from the Assiut University wind tunnel with maximum velocity of 4 m/s, and from subsonic wind tunnel at Belgrade University, with maximum air velocity of 45 m/s. Detailed comparisons for velocity distributions with these experimental results have shown very good conformity. Also, the three-parameter fitting methods were successfully established to define surface roughness length z 0 and the friction velocity u∗. Obtained results have shown that the established numerical model is able to substitute a remarkable number of expensive wind tunnel tests hours within the operational investigations of wind influence on the building structures

Aerodynamic analysis of a light aircraft at different design stages

Tokom aerodinamičkog projektovanja aviona, shodno njegovoj kategoriji i fazi razvoja projekta, potrebno je koristiti adekvatne proračunske metode i softverske alate. U slučaju lakih aviona, uobičajeno se koriste analitičke i semiempirijske metode u inicijalnoj fazi, kombinovane sa jednostavnim - neviskoznim CFD proračunskim modelima, dok se u kasnijim fazama obavljaju relativno kompleksne CFD analize sa uticajem viskoznosti. U današnje vreme se, u kategoriji lakih aviona, podrazumeva da savremeni proračunski alati za svaku od faza razvoja moraju biti adekvatno izabrani, tako da se njima dobijeni rezultati međusobno verifikuju i dopunjavaju. U radu su prikazane proračunske metode korišćene tokom aerodinamičke analize novog lakog aviona u različitim fazama njegovog razvoja i izvršeno je poređenje dobijenih rezultata, u cilju verifikacije ispunjenja navedenog uslova.During the evolution of an airplane aerodynamic design, proper calculation methods and software tools should be utilized, which correspond to the airplane category and project development level. In case of light aircraft, the general trend is the application of analytical and semiempirical methods at the initial stages, combined with simplified - inviscid CFD computational models, and fairly complex viscous CFD analyses at higher design levels. At the present stage of light aviation development, it is assumed that the contemporary design tools for each of those steps should be appropriate enough, so that they actually verify and additionally fine-tune each other's results. This paper describes the calculation tools and methods applied during the aerodynamic analyses of a new light aircraft at different development stages, and compares the results obtained by them, with the aim to verify and support the above statement, considering light aircraft aerodynamic design

Numerical modelling of velocity profile parameters of the atmospheric boundary layer simulated in wind tunnels

Experimental and numerical modeling and simulations of the wind influence within the atmospheric boundary layer are essential tools in optimum building structural design. Each of these methods, however, has both advantages and disadvantages. In experimental investigations performed in wind tunnels, reliable results can be obtained, but detailed information of the wind profile parameters, such as the surface roughness length z 0 or the friction velocity u∗, are difficult to determine. Numerical simulations, on other hand, easily yield any information of the wind velocity profile. However, the reliability of numerical results strongly depends on the established and adopted computational model. This paper presents the computational fluid dynamics (CFD) analysis of the atmospheric boundary layer simulated in subsonic wind tunnels using appropriate types of obstacles, based on the SST k-ω turbulence model with optimized unstructured mesh and optimum selection of relevant physical model parameters, performed in Ansys Fluent software. Results have been compared with the measurements from the Assiut University wind tunnel with maximum velocity of 4 m/s, and from subsonic wind tunnel at Belgrade University, with maximum air velocity of 45 m/s. Detailed comparisons for velocity distributions with these experimental results have shown very good conformity. Also, the three-parameter fitting methods were successfully established to define surface roughness length z 0 and the friction velocity u∗. Obtained results have shown that the established numerical model is able to substitute a remarkable number of expensive wind tunnel tests hours within the operational investigations of wind influence on the building structures

CFD modeling of supersonic airflow generated by 2D nozzle with and without an obstacle at the exit section

Modeliranje složenih nadzvučnih strujnih polja korišćenjem računara predstavlja jedan od najvećih izazova u oblasti CFD analiza. U radu su predstavljeni prvi koraci u numeričkoj analizi takvog strujanja, generisanog konvergentno- divergentnim mlaznikom sa Mahovim brojem M = 2.6 na izlazu iz mlaznika. Cilj je bio postići dobra poklapanja sa raspoloživim eksperimentalnim podacima, dobijenim tokom ispitivanja u nadzvučnom aerotunelu instituta VTI Žarkovo, gde su ispitivane mogućnosti vektorisanja potiska mlaznika sa vazduhom kao radnim fluidom, postavljanjem različitih tipova prepreka na izlazu iza mlaznika. U radu se analiziraju slučajevi strujanja sa slobodnim izlazom i sa jednim izabranim tipom prepreke na izlazu iz mlaznika. Za oba slučaja korišćene su strukturirane proračunske mreže za rešavanje RANS jednačina sa k-w SST turbulentnim modelom. Nakon kvalitativnih i kvantitativnih poređenja sa raspoloživim eksperimentalnim rezultatima, utvrđena su dobra poklapanja, pri čemu je CFD analiza bila u mogućnosti da pruži i dodatne podatke o strujnom polju, koji nisu mereni tokom eksperimenata.Computational modeling of complex supersonic airflow patterns is one of the greatest challenges in the domain of CFD analyses. The paper presents initial steps in numerical analysis of such flow, generated by convergentdivergent nozzle with Mach number M = 2.6 at nozzle exit. The aim was to achieve good agreements with available experimental data, obtained during supersonic wind tunnel tests at VTI Žarkovo institute, where nozzle thrust vectoring possibilities had been investigated using air as test fluid, by placing different types of obstacles at the exit section. Paper is focussed on free exit flow, and flow with one selected obstacle type. Using structured mesh for both cases, the RANS equations with k-w SST turbulent model have been applied. After quantitative and qualitative comparisons with available experimental data, good agreements have been obtained, where CFD was also able to provide additional flowfield data, not measuted during experiments

CFD modeling of supersonic airflow generated by 2D nozzle with and without an obstacle at the exit section

Modeliranje složenih nadzvučnih strujnih polja korišćenjem računara predstavlja jedan od najvećih izazova u oblasti CFD analiza. U radu su predstavljeni prvi koraci u numeričkoj analizi takvog strujanja, generisanog konvergentno- divergentnim mlaznikom sa Mahovim brojem M = 2.6 na izlazu iz mlaznika. Cilj je bio postići dobra poklapanja sa raspoloživim eksperimentalnim podacima, dobijenim tokom ispitivanja u nadzvučnom aerotunelu instituta VTI Žarkovo, gde su ispitivane mogućnosti vektorisanja potiska mlaznika sa vazduhom kao radnim fluidom, postavljanjem različitih tipova prepreka na izlazu iza mlaznika. U radu se analiziraju slučajevi strujanja sa slobodnim izlazom i sa jednim izabranim tipom prepreke na izlazu iz mlaznika. Za oba slučaja korišćene su strukturirane proračunske mreže za rešavanje RANS jednačina sa k-w SST turbulentnim modelom. Nakon kvalitativnih i kvantitativnih poređenja sa raspoloživim eksperimentalnim rezultatima, utvrđena su dobra poklapanja, pri čemu je CFD analiza bila u mogućnosti da pruži i dodatne podatke o strujnom polju, koji nisu mereni tokom eksperimenata.Computational modeling of complex supersonic airflow patterns is one of the greatest challenges in the domain of CFD analyses. The paper presents initial steps in numerical analysis of such flow, generated by convergentdivergent nozzle with Mach number M = 2.6 at nozzle exit. The aim was to achieve good agreements with available experimental data, obtained during supersonic wind tunnel tests at VTI Žarkovo institute, where nozzle thrust vectoring possibilities had been investigated using air as test fluid, by placing different types of obstacles at the exit section. Paper is focussed on free exit flow, and flow with one selected obstacle type. Using structured mesh for both cases, the RANS equations with k-w SST turbulent model have been applied. After quantitative and qualitative comparisons with available experimental data, good agreements have been obtained, where CFD was also able to provide additional flowfield data, not measuted during experiments

Computational simulation of air flow supersonic nozzle with obstacle at exit

U ovom radu se razmatra uticaj sklopnih operacija na izolacione karakteristike vakuumskih sklopnih elemenata. Razmatraju se sledeće sklopne operacije: uklop bez struje – isklop bez struje, uklop bez struje - uklop sa nominalnom strujom, uklop bez struje - isklop sa strujom kratkog spoja. Pri tome se ovaj uticaj ispituje na slučajne veličine ac probojni napon, impulsni probojni napon i na pretprobojne parametre V-4,V-5 i V-6 (dc naponi pri kojima je pretprobojna struja 10-4 A, 10-5 A i 10-6 A). Dobijeni efekti promene karakteristika nakon sklopnih operacija se porede sa odgovarajućim rezultatima dobijenim sa istim skopnim elementima kondicioniranih kontakata. Tako dobijeni rezultati se tumače preko mehanizma elektičnog pražnjenja u vakuumu. Osnovni rezultat, a ujedno i cilj rada, je ispitivanje relacija korelacije i regresije između eksperimentalno dobijenim statističkim uzorcima slučajne veličine ac i impulsni probojni napon i njima odgovarajućih statističkih uzoraka slučajnih veličina predprobojnih parametara V-4,V-5 i V-6. Ispitivanje se vrši na komercijalnim vakuumskim sklopnim elementima sa CuCr i CuBi kontaktima.This work considers the influence of switching operations on the insulating characteristics of vacuum circuit breakers. The following operations, all with circuit-making without current, have been taken into account: circuit-breaking without current, circuit-breaking with nominal current and circuit-breaking with short-circuit current. The influence of switching operations is examined for the random variables breakdown voltage (ac and pulse) and the prebreakdown parameters V-4, V-5, and V-6. Parameters V-4, V-5, and V-6 represent the dc voltage at which the pre-breakdown current takes values of 10-4, 10-5, and 10-6 A, respectively. Switching element characteristics after the switching operations are compared with the corresponding results obtained for switching element with conditioned contacts. Obtained results are analyzed through mechanisms of electrical discharges in vacuum. The main result is an examination of the correlation and regression between the experimentally obtained breakdown voltage (ac and pulse) random variable and its corresponding pre-breakdown parameters V-4, V-5, and V-6, respectively. Statistical samples created by using this method do not require the repetition of switching operations and therefore the dielectric strength of the vacuum insulation is kept in its initial state. The examination is carried out on commercial vacuum switching elements with CuCr and CuBi contacts

Initial development of the hybrid semielliptical-dolphin airfoil

Iosif Taposu has formulated a mathematical model and generated a family of air-foils whose geometry resembles the dolphin shape. These airfoils are characterized by a sharp leading edge and experiments have proven that they can achieve better aerodynamic characteristics at very high angles of attack than certain classical airfoils, with the nose geometry inclined downwards. On the other hand, they have not been applied to any commercial general aviation aircraft. The authors of this paper have been motivated to compare the aerodynamic characteristics of widely used NACA 2415 airfoil with Taposu???s Dolphin that would have the same princi-pal geometric characteristics. A CFD calculation model has been established and applied on NACA 2415. The results were compared with NACA experiments and very good agreements have been achieved in the major domains of lift and polar curves. The same CFD model has been applied on the counterpart Dolphin 2415. Results have shown that the Dolphin has a slightly higher lift/drag ratio in the lift coefficient domain 0.1-0.35 than NACA. On the other hand, at higher and lower lift coefficients, its aerodynamic characteristics were drastically below those of the NACA section, due to the unfavorable influence of the Dolphin???s sharp nose. A series of the Dolphin???s leading edge modifications has been investigated, gradually improving its aerodynamics. Finally, version M4, consisting of about 70% of Dol-phin???s original rear domain and 30% of the new nose shape, managed to exceed the NACA???s characteristics, thus paving the way to investigate the Dolphin hybrids that could be suitable for the general aviation industry

Computational simulation of air flow supersonic nozzle with obstacle at exit

U ovom radu se razmatra uticaj sklopnih operacija na izolacione karakteristike vakuumskih sklopnih elemenata. Razmatraju se sledeće sklopne operacije: uklop bez struje – isklop bez struje, uklop bez struje - uklop sa nominalnom strujom, uklop bez struje - isklop sa strujom kratkog spoja. Pri tome se ovaj uticaj ispituje na slučajne veličine ac probojni napon, impulsni probojni napon i na pretprobojne parametre V-4,V-5 i V-6 (dc naponi pri kojima je pretprobojna struja 10-4 A, 10-5 A i 10-6 A). Dobijeni efekti promene karakteristika nakon sklopnih operacija se porede sa odgovarajućim rezultatima dobijenim sa istim skopnim elementima kondicioniranih kontakata. Tako dobijeni rezultati se tumače preko mehanizma elektičnog pražnjenja u vakuumu. Osnovni rezultat, a ujedno i cilj rada, je ispitivanje relacija korelacije i regresije između eksperimentalno dobijenim statističkim uzorcima slučajne veličine ac i impulsni probojni napon i njima odgovarajućih statističkih uzoraka slučajnih veličina predprobojnih parametara V-4,V-5 i V-6. Ispitivanje se vrši na komercijalnim vakuumskim sklopnim elementima sa CuCr i CuBi kontaktima.This work considers the influence of switching operations on the insulating characteristics of vacuum circuit breakers. The following operations, all with circuit-making without current, have been taken into account: circuit-breaking without current, circuit-breaking with nominal current and circuit-breaking with short-circuit current. The influence of switching operations is examined for the random variables breakdown voltage (ac and pulse) and the prebreakdown parameters V-4, V-5, and V-6. Parameters V-4, V-5, and V-6 represent the dc voltage at which the pre-breakdown current takes values of 10-4, 10-5, and 10-6 A, respectively. Switching element characteristics after the switching operations are compared with the corresponding results obtained for switching element with conditioned contacts. Obtained results are analyzed through mechanisms of electrical discharges in vacuum. The main result is an examination of the correlation and regression between the experimentally obtained breakdown voltage (ac and pulse) random variable and its corresponding pre-breakdown parameters V-4, V-5, and V-6, respectively. Statistical samples created by using this method do not require the repetition of switching operations and therefore the dielectric strength of the vacuum insulation is kept in its initial state. The examination is carried out on commercial vacuum switching elements with CuCr and CuBi contacts

Comparative CFD analysis of a 2D supersonic nozzle flow with jet tab and jet vane

U okviru ove studije, ustanovljen je CFD (Computational Fluid Dynamics) proračunski model za potrebe analize kompleksnog nadzvučnog strujnog polja generiranog 2D konvergentno-divergentnim mlaznikom. U cilju simulacije upravljanja vektorom potiska (UVP) raketnih motora, najprije je rabljen spojler, postavljen u nekoliko položaja do maksimalnih 30% zasjenčenja površine izlaznog presjeka, bez procjepa i s procjepom u odnosu na izlaz. Proračunski rezultati uspoređeni su s raspoloživim eksperimentalnim rezultatima kvantitativno i kvalitativno, pri čemu su u oba slučaja dobivena zadovoljavajuća poklapanja. Jednaka CFD podešavanja su zatim uporabljena za kompjutersku analizu još jednog tipa UVP – mlaznog krilca, koje je analizirano u četiri različite usvojene konfiguracije u odnosu na mlaznik. Stabilna konvergencija rješenja je postignuta za sve kutove otklona mlaznih krilaca do 40°. Provedeni proračuni omogućili su usporedbu dva razmatrana tipa UVP, kako u smislu ostvarenog zakretanja sile potiska, tako i u kontekstu gubitaka potiska.In this study, a CFD (Computational Fluid Dynamics) computational model has been established, with the aim to properly simulate complex supersonic flow generated by a 2D convergent-divergent nozzle. For the purpose of rocket engine thrust vector control (TVC) simulations, initially several jet tab positions were used to generate up to 30% shadowing of the nozzle exit, without and with a gap between tab and exit. Numerical results were compared with the existing experimental data, both quantitatively and qualitatively, and fair agreements have been obtained in both senses. The same CFD settings have then been applied for the computational analysis of another TVC type – the jet vane, which was analysed in four different adopted configurations with respect to the nozzle. Stable convergence of solutions has been achieved, up to 40° of vane deflections. Performed calculations have enabled comparisons of the two considered TVC types, in the sense of the achieved thrust force deflections, and thrust losses