Model-based stagnation pressure control in a supersonic wind tunnel

Upravljanje parametrima strujanja u aerotunelima je oblast intenzivnog istraživanja poslednjih godina, sa ciljem poboljšanja kvaliteta i efikasnosti rada aerotunelskih instalacija. Ovaj rad predstavlja pokušaj da se doprinese boljem razumevanju upravljanja zaustavnim pritiskom u supersoničnim instalacijama prekidnog dejstva. Razmotrena je strategija upravljanja zaustavnim pritiskom u aerotunelu T-38 Vojnotehničkog instituta u Beogradu. Poboljšani matematički model supersoničnih aerotunelskih instalacija je predložen i primenjen na aerotunel T-38. Tačnost sa kojom matematički model predviđa odziv instalacije u uslovima supersoničnog strujanja demonstrirana je poređenjem podataka iz simulacija i eksperimenata. Matematički model je upotrebljen za uvođenje izmenjenog algoritma upravljanja u polazni upravljački sistem aerotunela T-38. Aerotunelski eksperimenti su potvrdili predviđanja modela u pogledu smanjenja vremena uspostavljanja strujanja i povećanja raspoloživog vremena za merenje, čime je postignuto značajno poboljšanje efikasnosti rada aerotunela.The flow parameters control in wind tunnels is an area of intense research in recent years, with the aim of improving quality and efficiency of the wind tunnel operation. In this paper, an attempt is made to contribute to a better understanding of the stagnation pressure control in supersonic blowdown-type facilities. The stagnation pressure control strategy in the VTI Belgrade T-38 wind tunnel is discussed. An improved mathematical model for a supersonic wind tunnel is suggested and applied to the T-38 facility. Comparisons of simulation and experimental data are made to demonstrate accurate prediction of the facility response in supersonic flow conditions by the mathematical model. The model is used to incorporate a modified feedforward control in the original T-38 wind tunnel control system. The actual wind tunnel tests confirm model-predicted decrease of flow stabilization time and increase of available measurement time, bringing significant improvement in the wind tunnel operation efficiency

Model-based stagnation pressure control in a supersonic wind tunnel

Upravljanje parametrima strujanja u aerotunelima je oblast intenzivnog istraživanja poslednjih godina, sa ciljem poboljšanja kvaliteta i efikasnosti rada aerotunelskih instalacija. Ovaj rad predstavlja pokušaj da se doprinese boljem razumevanju upravljanja zaustavnim pritiskom u supersoničnim instalacijama prekidnog dejstva. Razmotrena je strategija upravljanja zaustavnim pritiskom u aerotunelu T-38 Vojnotehničkog instituta u Beogradu. Poboljšani matematički model supersoničnih aerotunelskih instalacija je predložen i primenjen na aerotunel T-38. Tačnost sa kojom matematički model predviđa odziv instalacije u uslovima supersoničnog strujanja demonstrirana je poređenjem podataka iz simulacija i eksperimenata. Matematički model je upotrebljen za uvođenje izmenjenog algoritma upravljanja u polazni upravljački sistem aerotunela T-38. Aerotunelski eksperimenti su potvrdili predviđanja modela u pogledu smanjenja vremena uspostavljanja strujanja i povećanja raspoloživog vremena za merenje, čime je postignuto značajno poboljšanje efikasnosti rada aerotunela.The flow parameters control in wind tunnels is an area of intense research in recent years, with the aim of improving quality and efficiency of the wind tunnel operation. In this paper, an attempt is made to contribute to a better understanding of the stagnation pressure control in supersonic blowdown-type facilities. The stagnation pressure control strategy in the VTI Belgrade T-38 wind tunnel is discussed. An improved mathematical model for a supersonic wind tunnel is suggested and applied to the T-38 facility. Comparisons of simulation and experimental data are made to demonstrate accurate prediction of the facility response in supersonic flow conditions by the mathematical model. The model is used to incorporate a modified feedforward control in the original T-38 wind tunnel control system. The actual wind tunnel tests confirm model-predicted decrease of flow stabilization time and increase of available measurement time, bringing significant improvement in the wind tunnel operation efficiency

Design criterion to select adequate control algorithm for electro-hydraulic actuator applied to rocket engine flexible nozzle thrust vector control under specific load

Rad razmatra problematiku kako na najbolji način izabrati algoritam upravljanja za elektro- hidraulični aktuator sa definisanim opterećenjem. Polazi se od pretpostavke idealnog algoritma upravljanja koji se prilagođava stvarnoj konfiguraciji elektrohidrauličnog aktuatora i definisanom opterećenju. Razmatra se netipično fleksibilno opterećenje, viskozoelastično, sa znatnim histerezisom koji dodatno zavisi od vremena odnosno temperature. Predlažu se dva načina modelovanja opterećenja i prikazuje se koliko opcije modelovanja opterećenja utiču na stvarni odziv aktuatorskog sistema. U razmatranom slučaju glavni poremećaj je spoljna sila prouzrokovana realnim oscilacijama sile potiska.The paper presents the challenge of finding the best criterion in selecting adequate control algorithm for electro-hydraulic actuator with a defined load. The ideal control algorithm that adapts to the actual configuration of electro-hydraulic actuator and defined load is used as an initial assumption. Atypical flexible load that is viscose-elastic, with a significant level of hysteresis that also depends on time and temperature is considered as well. Two types of load modeling approaches are proposed, accompanied by presentation on how load modeling options affect the actual response of an actuator system. The main disturbance, in this case, is considered to be external force generated by thrust force real oscillations

Measurement of the direct damping derivative in roll of the two calibration missile models

U ovom radu opisano je merenje prigušnog derivativa stabilnosti u valjanju u aerotunelu T- 38. Prikazani su rezultati dobijeni na dva kalibraciona modela: Basic Finner Model i Modified Basic Finner Model. Uređaj za merenje derivativa stabilnosti je uređaj sa prinudnim oscilacijama modela i to sa primarnim oscilatornim kretanjem u ravni valjanja. Pobudni moment u valjanju meren je petokomponentnom aerovagom sa mernim trakama. Ova aerovaga je projektovana i izrađena za dinamička aerotunelska merenja. Amplitude i fazni stavovi pobudnog momenta određeni su u frekventnom domenu primenom kros-korelacione metode. Rezultati dobijeni u aerotunelu T-38 upoređeni su sa objavljenim eksperimentalnim rezultatima dobijenim u Arnold Engineering Development Center-von Karman 4ft aerotunelu.Measurement of the direct damping derivative in roll in the T-38 wind tunnel is described in this paper. The T-38 wind tunnel data for the Basic Finner Model and Modified Basic Finner model are shown. The forced oscillation technique was used for these measurements. The roll apparatus for the stability derivatives measurement is a full-model forced oscillation apparatus with primary angular oscillation around a longitudinal axis of the model. The excitation moment in roll was measured with the five- component strain gauge balance. This balance was designed and built for the wind tunnel dynamic measurements. The amplitudes and phase shifts of the excitation moment were calculated in frequency domain by applying cross-correlation technique. The T-38 wind tunnel results are compared with published experimental results of the Arnold Engineering Development Center-von Karman 4ft wind tunnel

Spojna sredstva sistema 'Huck BobTail' - novo rešenje za visokovredne zavrtnjeve sa zaključavanjem

Alcoa Fastening Systems, introduces the Huck BobTail, representing the most advanced fastening technology to date. Recognized as the next-generation lockbolt, the Huck BobTail delivers 5 times the fatigue strength of conventional nuts and bolts, and is engineered to provide the highest level of strength, reliability, and vibration-resistant performance. Engineered to meet the challenges of a wide range of assembly applications, BobTail offers high performance and easy, quick installation.Firma 'Alcoa Fastening Systems' konstruisala je 'Huck BobTail' sistem mehaničkih spojnih sredstava i predstavila ga kao jednu od najnaprednijih tehnologija spajanja do danas. Prepoznat kao zaključavajući zavrtanj (antivandal) naredne generacije, 'Huck BobTail' donosi pet puta veću čvrstoću na zamor od standardnih zavrtnjeva sa navrtkom, a konstruisan je tako da pruži visoku čvrstoću, pouzdanost i otpornost na vibracije i u najekstremnijim uslovima. Konstruisan da zadovolji širok spektar sistema za spajanje, 'BobTail' odlikuju visoke performance kao i jednostavna i brza ugradnja

COMPUTATIONAL AND EXPERIMENTAL INVESTIGATION INTO SUBSONIC FLOW AROUND A FINNED OGIVE CYLINDER

Experimental and numerical investigation into the flow around an ogive cylinder with fins (missile calibration model) was conducted for Mach 0.6 flow. The computational results were compared to the results of pressure-distribution and force/moments measurements conducted in the T-38 trisonic blowdown wind tunnel of the Military Technical Institute of Serbia. In addition to the pressure distribution along the model, the base pressure was computed and compared to experimental data. Standard pre-processing techniques and a realizable k-ε turbulence model with enhanced wall treatment were used in the flow computations. The numerical simulation results achieved with moderate hardware resources were found to be in relatively good agreement with the experiment if high separation in the base region and related issues that CFD analysts are faced with are taken into account

Two-dimensional wind tunnel measurement corrections by the singularity method

Razvijena je metoda za korigiranje raspodjele koeficijenta pritiska oko aeroprofila u cilju obrade rezultata dobivenih mjerenjima pritiska na modelu u aerotunelu. Zbog utjecaja interferencije sa zidovima radnog dijela aerotunela, raspodjela koeficijenta pritiska neposredno dobivena mjerenjima korigira se numerički. U ovom radu, aeroprofil NACA 0012 aproksimiran je linijskim vrtložnim segmentima, koji se preslikavaju kao lik u ogledalu dovoljno puta u odnosu na položaje poda i plafon radnog dijela, da bi se modeliralo strujanje oko aeroprofila u neporoznom radnom dijelu aerotunela. Proračun se zatim vrši kako za slučaj strujanja sa prisustvom zidova, tako i za opstrujavanje u slobodnoj atmosferi. Razlika u numerički određenoj raspodjeli koeficijenata pritiska za ova dva slučaja se u odgovarajućim točkama superponira sa raspodjelom pritisaka izmjerenom u aerotunelu, pri istim nominalnim uslovima strujanja i napadnom uglu, čime se dobija korigirana eksperimentalna raspodjela pritisaka. Koeficijent uzgona se zatim izračunava iz tako korigirane raspodjele koeficijenata pritiska. Vrijednosti korekcija generalno rastu sa smanjenjem relativne visine radnog dijela aerotunela. Rad je fokusiran na verifikaciju faktora korekcije gradijenta uzgona, gdje su vrlo dobra poklapanja dobijena u usporedbi s nekoliko poznatih klasičnih metoda korekcije.The correction method for pressure coefficient distribution around an airfoil is developed for the purpose of the postprocessing of wind tunnel data, obtained from the model pressure measurements. Pressure coefficient distribution around the airfoil, directly obtained by wind tunnel measurements, is corrected numerically in order to compensate for the interference effects of the wind tunnel test section walls. In this paper, the airfoil NACA0012 is approximated by linear vortex segments, which are then mirrored using sufficient number of images with respect to the ceiling and the floor of the test section, to model the flow pattern around an airfoil in the wind tunnel test section with solid walls. Flow calculations, both with the tunnel wall presence and in the free stream, are then performed. The numerically obtained pressure coefficient difference between these two cases should be superimposed to the pressure coefficient distribution measured in the wind tunnel, for the same nominal airflow parameters and angle of attack, at the corresponding points, resulting in the corrected experimental pressure coefficient distribution. The values of corrections generally increase with the reduction of the wind tunnel test section relative height. The paper is focused on the verification of lift curve slope corrections, where very good agreements have been obtained with several well-known classical correction methods

Analysis of the possibility of increasing sting stiffness in the T-38 wind tunnel

Aerotunelski model i deformacije držača modela tokom eksperimenata u aerotunelu T-38 imaju značajan utjecaj na točnost mjerenja. Radi dobivanja visoke točnosti mjerenja poželjno je da deformacije budu što manje. Mogućnost da se uporabom visokokvalitetnog čelika za izradu držača modela utječe na razinu naprezanja i deformacija je iscrpljena time što se u aerotunelu T-38 koriste visoko kvalitetni maraging čelici. Na osnovu velikog broja provedenih eksperimenata utvrđeno je da je postizanje manjih deformacija moguće povećanjem krutosti držača modela. U ovom radu se razmatraju kombinacije različitih materijala s maraging čelikom koji je osnovni materijal za izradu držača modela. Neophodno je odabrati kombinaciju materijala koja daje najveću zahtijevanu krutost i dopuštenu razinu naprezanja u kritičnim presjecima držača modela.Wind tunnel model and sting deflections during experiment in the T-38 wind tunnel have a significant influence on the measurement quality. It is necessary to reduce deflections due to higher accuracy of measurements achievement. High quality stainless steel is already widely used in the T-38 wind tunnel so there is no possibility for further influence to sting stress and deflection level. Based on the great number of performed experiments it is established that sting deflection can be reduced by increasing the sting stiffness. In this paper different material combinations with maraging stainless steel, which is base material for sting manufacturing, are considered. It is necessary to select combination of materials which produces the biggest required stiffness and allowed level of stress in critical sections of the sting