Some practical issues in the computational design of airfoils for the helicopter main rotor blades

Very important requirement for the helicopter rotor airfoils is zero, or nearly zero moment coefficient about the aerodynamic center. Unlike the old technologies used for metal blades, modern production involving application of plastic composites has imposed the necessity of adding a flat tab extension to the blade trailing edge, thus changing the original airfoil shape. Using computer program TRANPRO, the author has developed and verified an algorithm for numerical analysis in this design stage, applied it on asymmetrical reflex camber airfoils, determined the influence of angular tab positioning on the moment coefficient value and redesigned some existing airfoils to include properly positioned tabs that satisfy very low moment coefficient requirement.

Some practical issues in the computational design of airfoils for the helicopter main rotor blades

Jedan od veoma važnih zahteva koji aeroprofili rotora helikoptera treba da ispune jeste da koeficijent momenta oko aerodinamičkog centra mora približno biti jednak nuli. Za razliku od starijih tehnologija, korišćenih u proizvodnji metalnih lopatica, savremene izvedbe koje se baziraju na primeni plastičnih kompozita zahtevaju da se na izlaznoj ivici doda ravan repić, čime se menja izvorni oblik aeroprofila. Uz pomoć kompjuterskog programa TRANPRO, autor je razvio i verifikavao algoritam za ovu fazu projektovanja, namenjen promeni na nesimetričnim aeroprofilima sa srednjom linijom u obliku latiničnog slova "S", kvantifikavao globalni uticaj ugaonog položaja repića na promenu momenta oko aerodinamičkog centra, a zatim reprojektovao nekoliko aeroprofila kojima je dodao repić na takav način da je zahtev za malom vrednošću ovog koeficijenta momenta u potpunosti ispunjen.Very important requirement for the helicopter rotor airfoils is zero, or nearly zero moment coefficient about the aerodynamic center. Unlike the old technologies used for metal blades, modern production involving application of plastic composites has imposed the necessity of adding a flat tab extension to the blade trailing edge, thus changing the original airfoil shape. Using computer program TRANPRO, the author has developed and verified an algorithm for numerical analysis in this design stage, applied it on asymmetrical reflex camber airfoils, determined the influence of angular tab positioning on the moment coefficient value and redesigned some existing airfoils to include properly positioned tabs that satisfy very low moment coefficient requirement

Improved numerical calculation of the airfoil transonic drag applied within a zonal flowfield modeling concept

Pri projektovanju savremenih komercijalnih vazduhoplova visoka ekonomičnost leta jedan je od najbitnijih zahteva koje treba ispuniti. Pored izbora ekonomičnih motora, vrlo bitna stavka za zadovoljenje ovog uslova je i primena savremenih tehnika pri aerodinamičkom projektovanju. Veliki broj ovih vazduhoplova krstari brzinama koje su nešto manje od brzine zvuka, pa je uzgonske površine i njihove aeroprofile potrebno optimizirati prevashodno za ovaj domen. Jedan od prvih koraka u tom procesu je izbor ili namensko projektovanje aeroprofila za krilo i ostale uzgonske površine konkretne letelice koji će proizvoditi što manji talasni otpor u krstarećem letu. Numerička optimizacija aeroprofila danas predstavlja izuzetno važan deo tog postupka. Algoritam prikazan u ovom radu omogućava numerički proračun talasnog otpora kako na postojećim tako i na aeroprofilima koji se namenski prave za određenu letelicu i prevashodno je namenjen operativnom aerodinamičkom projektovanju vazduhoplova. Algoritam je relativno jednostavan i vrlo pouzdan, što je pokazano poređenjem rezultata koje on daje u okviru programa nazvanog Tranpro sa eksperimentalnim rezultatima iz nekoliko najkompetentnijih svetskih vazduhoplovnih centara koji se bave ovom problematikom .Very high cost efficiency of the flight is a crucial requirement specially in the contemporary commercial airplane design. Beside the low engine fuel consumption, advanced aerodynamics is another dominant factor which must be satisfied to fulfill this request. Many of these aircraft cruise at speeds slightly lower than the speed of sound, so their lifting surfaces and corresponding airfoils must be optimized primarily for this domain. One of the first steps in that process is selection or even design of the customized airfoils for the particular wing and other lifting surfaces that will produce the least possible shock wave drag in cruising flight. Nowadays the numerical airfoil optimization is very important part in that process. Algorithm presented in this paper enables the numerical calculation of wave drag both for the existing and the airfoils designed specially for a certain aircraft, and it is primarily aimed for use in the operational aircraft design. This algorithm is fairly simple and very reliable, which has been proven by comparing it’s results, obtained through the computer program Tranpro, with the experimental results for airfoils tested at several most competent aeronautical institutions throughout the world

Improved numerical calculation of the airfoil transonic drag applied within a zonal flowfield modeling concept

Pri projektovanju savremenih komercijalnih vazduhoplova visoka ekonomičnost leta jedan je od najbitnijih zahteva koje treba ispuniti. Pored izbora ekonomičnih motora, vrlo bitna stavka za zadovoljenje ovog uslova je i primena savremenih tehnika pri aerodinamičkom projektovanju. Veliki broj ovih vazduhoplova krstari brzinama koje su nešto manje od brzine zvuka, pa je uzgonske površine i njihove aeroprofile potrebno optimizirati prevashodno za ovaj domen. Jedan od prvih koraka u tom procesu je izbor ili namensko projektovanje aeroprofila za krilo i ostale uzgonske površine konkretne letelice koji će proizvoditi što manji talasni otpor u krstarećem letu. Numerička optimizacija aeroprofila danas predstavlja izuzetno važan deo tog postupka. Algoritam prikazan u ovom radu omogućava numerički proračun talasnog otpora kako na postojećim tako i na aeroprofilima koji se namenski prave za određenu letelicu i prevashodno je namenjen operativnom aerodinamičkom projektovanju vazduhoplova. Algoritam je relativno jednostavan i vrlo pouzdan, što je pokazano poređenjem rezultata koje on daje u okviru programa nazvanog Tranpro sa eksperimentalnim rezultatima iz nekoliko najkompetentnijih svetskih vazduhoplovnih centara koji se bave ovom problematikom .Very high cost efficiency of the flight is a crucial requirement specially in the contemporary commercial airplane design. Beside the low engine fuel consumption, advanced aerodynamics is another dominant factor which must be satisfied to fulfill this request. Many of these aircraft cruise at speeds slightly lower than the speed of sound, so their lifting surfaces and corresponding airfoils must be optimized primarily for this domain. One of the first steps in that process is selection or even design of the customized airfoils for the particular wing and other lifting surfaces that will produce the least possible shock wave drag in cruising flight. Nowadays the numerical airfoil optimization is very important part in that process. Algorithm presented in this paper enables the numerical calculation of wave drag both for the existing and the airfoils designed specially for a certain aircraft, and it is primarily aimed for use in the operational aircraft design. This algorithm is fairly simple and very reliable, which has been proven by comparing it’s results, obtained through the computer program Tranpro, with the experimental results for airfoils tested at several most competent aeronautical institutions throughout the world

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

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

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