Influence of simple harmonic speed variations on the Vuk-T sailplane approach paths and distances

Ukoliko iz bilo kog tehničkog razloga vazdušne kočnice prestanu da funkcionišu tokom leta, najkritičnija faza u proceduri sletanja jedrilice je finalni prilaz. Pored leta sa bočnim klizanjem, kada se disipacija energije vrši kroz povećanje bočne sile otpora, drugo moguće rešenje ovog problema je ponuđeno u literaturi, gde je pokazano da se dužina prilaza može minimizirati primenom složenih oscilatornih putanja leta. Međutim, let po takvim putanjama zahteva izuzetno letačko umeće. Nasuprot tome, u ovom radu izvršena je analiza jednostavnijih prilaznih putanja, baziranih na harmonijskim promenama brzine, koje je mnogo lakše operativno reprodukovati u letu. U radu je prikazan proračunski algoritam koji omogućava brzu konvergenciju rešenja i analizirana su numerička rešenja za nekoliko tipičnih slučajeva. Kao primer korišćeni su podaci za jedrilicu Vuk-T. Dobijeni rezultati pokazuju nešto manja skraćenja putanja, ali jednostavnost primene u praksi i veća bezbednost predloženih tehnika letenja čini ih korisnim rešenjima u slučaju pomenutih problema.When for any technical reason spoilers become inoperable in flight, the most critical phase of a sailplane landing procedure is final approach. Besides the sideslipping flight possibility, where energy is dissipated through the increased sideforce drag, another solution for this problem has been offered in literature, showing that the landing distance could be minimized using rather complex oscillating flight paths. The problem is that performing such paths in practice would require exceptional piloting skills. Instead of that, in this paper much simpler approach profiles have been analyzed, based on the simple harmonic speed variations, which could much easier be reproduced in practice. After establishing a quick convergence algorithm, numerical solutions for several typical cases, taking the Vuk-T sailplane as an example, have been presented. Although distance reductions are generally smaller than obtained by distance-minimizing techniques, their operational simplicity and higher safety prove them as valuable solutions for this kind of problems

Influence of simple harmonic speed variations on the Vuk-T sailplane approach paths and distances

Ukoliko iz bilo kog tehničkog razloga vazdušne kočnice prestanu da funkcionišu tokom leta, najkritičnija faza u proceduri sletanja jedrilice je finalni prilaz. Pored leta sa bočnim klizanjem, kada se disipacija energije vrši kroz povećanje bočne sile otpora, drugo moguće rešenje ovog problema je ponuđeno u literaturi, gde je pokazano da se dužina prilaza može minimizirati primenom složenih oscilatornih putanja leta. Međutim, let po takvim putanjama zahteva izuzetno letačko umeće. Nasuprot tome, u ovom radu izvršena je analiza jednostavnijih prilaznih putanja, baziranih na harmonijskim promenama brzine, koje je mnogo lakše operativno reprodukovati u letu. U radu je prikazan proračunski algoritam koji omogućava brzu konvergenciju rešenja i analizirana su numerička rešenja za nekoliko tipičnih slučajeva. Kao primer korišćeni su podaci za jedrilicu Vuk-T. Dobijeni rezultati pokazuju nešto manja skraćenja putanja, ali jednostavnost primene u praksi i veća bezbednost predloženih tehnika letenja čini ih korisnim rešenjima u slučaju pomenutih problema.When for any technical reason spoilers become inoperable in flight, the most critical phase of a sailplane landing procedure is final approach. Besides the sideslipping flight possibility, where energy is dissipated through the increased sideforce drag, another solution for this problem has been offered in literature, showing that the landing distance could be minimized using rather complex oscillating flight paths. The problem is that performing such paths in practice would require exceptional piloting skills. Instead of that, in this paper much simpler approach profiles have been analyzed, based on the simple harmonic speed variations, which could much easier be reproduced in practice. After establishing a quick convergence algorithm, numerical solutions for several typical cases, taking the Vuk-T sailplane as an example, have been presented. Although distance reductions are generally smaller than obtained by distance-minimizing techniques, their operational simplicity and higher safety prove them as valuable solutions for this kind of problems

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

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

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

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

Investigation of the pressure distribution in a 2D rocket nozzle with a mechanical system for thrust vector control (TVC)

This paper introduces a new physical model of the gas flow through the 2D nozzle with the tilted obstacle in exit section. Experimental research on the 2D full span model in the supersonic indraft tunnel, which includes over three hundred tunnel runs, are presented. Variable geometric parameters were: nozzle shadow area, obstacle-nozzle wall angle, obstacle-nozzle gap and nozzle area ratio. In its conclusion, the paper discusses results and presents some suggestions for the future research

Numerical simulation as a tool for optimizing tool geometry for rubber pad forming process

Pri proizvodnji novog dela može se primeniti pristup probnih pokušaja u cilju dobijanja dela bez defekata, a to u velikoj meri zavisi od iskustva radnika. U ovoj fazi iskustvo projektanta i proizvođača treba da pruži važnu podršku za smanjenje broja pokušaja i samim tim doprinese minimizaciji vremena odziva i troškova uz maksimizaciju ujednačenosti proizvoda. Obrada lima u alatima sa gumenim jezgrom značajno unapređuje formabilnost pripremka zbog toga što su kontaktne površine između krutog dela alata i dela alata sa gumenim jezgrom fleksibilne. Ovaj metod omogućava izradu delova od lima sa kompleksnim konturama uz relativno male troškove zbog toga što je potreban samo jedan deo alata od čvrstog materijala. U avio industriji proizvode se delovi od lima u malim količinama tako da se ne isplate veće investicije u alate i projektovanje procesa. Iz ovih razloga neophodna je primena simulacija tehnološkog procesa metodom konačnih elemenata tokom konceptualnog projektovanja.To produce a new component there are a trial and error stage to obtain a part without defects, which strongly depends on operator's experience. At this stage, the experience of designer and manufacturers should give an important aid to reduce trials to realize the minimization of response time and cost with maximization of the product equality. Rubber pad forming highly improves the formability of the blank because the contact surfaces between the rigid die and the rubber pad is flexible. This method enables to produce sheet metal components with complex contour by relatively low cost because only one rigid die is required. However, in aerospace field, parts are produced in small sheet metal bending and small number of components. It means that it is not worthy for large investments in tools and process design. For these reasons, it is necessary to use FE simulation of manufacturing process during the conceptual design

Numerical simulation as a tool for optimizing tool geometry for rubber pad forming process

Pri proizvodnji novog dela može se primeniti pristup probnih pokušaja u cilju dobijanja dela bez defekata, a to u velikoj meri zavisi od iskustva radnika. U ovoj fazi iskustvo projektanta i proizvođača treba da pruži važnu podršku za smanjenje broja pokušaja i samim tim doprinese minimizaciji vremena odziva i troškova uz maksimizaciju ujednačenosti proizvoda. Obrada lima u alatima sa gumenim jezgrom značajno unapređuje formabilnost pripremka zbog toga što su kontaktne površine između krutog dela alata i dela alata sa gumenim jezgrom fleksibilne. Ovaj metod omogućava izradu delova od lima sa kompleksnim konturama uz relativno male troškove zbog toga što je potreban samo jedan deo alata od čvrstog materijala. U avio industriji proizvode se delovi od lima u malim količinama tako da se ne isplate veće investicije u alate i projektovanje procesa. Iz ovih razloga neophodna je primena simulacija tehnološkog procesa metodom konačnih elemenata tokom konceptualnog projektovanja.To produce a new component there are a trial and error stage to obtain a part without defects, which strongly depends on operator's experience. At this stage, the experience of designer and manufacturers should give an important aid to reduce trials to realize the minimization of response time and cost with maximization of the product equality. Rubber pad forming highly improves the formability of the blank because the contact surfaces between the rigid die and the rubber pad is flexible. This method enables to produce sheet metal components with complex contour by relatively low cost because only one rigid die is required. However, in aerospace field, parts are produced in small sheet metal bending and small number of components. It means that it is not worthy for large investments in tools and process design. For these reasons, it is necessary to use FE simulation of manufacturing process during the conceptual design

Investigation of the pressure distribution in a 2D rocket nozzle with a mechanical system for thrust vector control (TVC)

This paper introduces a new physical model of the gas flow through the 2D nozzle with the tilted obstacle in exit section. Experimental research on the 2D full span model in the supersonic indraft tunnel, which includes over three hundred tunnel runs, are presented. Variable geometric parameters were: nozzle shadow area, obstacle-nozzle wall angle, obstacle-nozzle gap and nozzle area ratio. In its conclusion, the paper discusses results and presents some suggestions for the future research