MODELAREA ȘI SIMULAREA NUMERICĂ A SIAJULUI TURBULENT AL AERONAVELOR

  CUPRINS:
1. Consideratii privind importanta studiului siajului aeronavelor1
1.1. Introducere1
1.2. Exemple de accidente produse din cauza siajului aeronavelor8
1.3. Modalitati de diminuare a riscurilor de aparitie a accidentelor produse din cauza siajului aeronavelor 10

2. Metode de reprezentare a siajului aeronavelor12
2.1. Introducere12
2.2. Generarea vartejurilor longitudinale contrarotative13
2.3. Modele matematice pentru reprezentarea vartejurilor izolate21
2.3.1. Vartej de tip Rankine21
2.3.2. Vartej de tip Lamb-Oseen24
2.4. Modele matematice pentru reprezentarea vartejurilor contrarotative29
2.4.1. Dipolul Lamb-Chaplygin29
2.4.2. Superpozitia de vartejuri izolate31
2.4.3. Serii de imagini de vartejuri33

3. Mecanisme de instabilitate turbionara36
3.1. Introducere36
3.2. Mecanisme de instabilitate caracterizate de lungime de unda mare36
3.2.1. Stabilitatea unui filament turbionar rectiliniu36
3.2.2. Instabilitate de tip Crow39
3.3. Mecanisme de instabilitate caracterizate de lungime de unda mica50
3.3.1. Stabilitatea nucleului vartejurilor siajului50
3.3.2. Instabilitatea eliptica53

4. Metode numerice pentru simularea curgerilor turbulente59
4.1. Introducere59
4.2. Ecuatiile curgerii turbulente60
4.2.1. Ecuatia de continuitate60
4.2.2. Ecuatiile cantitatii de miscare61
4.3. Simularea numerica directa61
4.4. Metoda simularii numerice a vartejurilor63
4.4.1. Filtre utilizate pentru metoda simularii vartejurilor65
4.4.2. Ecuatiile Navier-Stokes filtrate66
4.4.3. Descompunerea termenului neliniar67
4.4.4. Modelarea structurilor turbulente mici68

5. Vartej longitudinal izolat74
5.1. Introducere74
5.2. Propagarea turbulentei in interiorul unui vartej izolat83
5.2.1. Curgerea de baza84
5.2.2. Curgerea perturbata la exteriorul vartejului principal89
5.2.3. Curgerea perturbata la interiorul vartejului principal103
5.2.4. Curgere perturbata in tot domeniul106

6. Metode de generare numerica a turbulentei109
6.1. Introducere109
6.2. Turbulenta omogena izotropa109
6.3. Generarea turbulentei de tip zgomot alb112
6.4. Generarea turbulentei sintetice113
6.5. Generarea turbulentei in prezenta solului116
6.5.1. Domeniul de calcul. Conditii initiale. Conditii la limita116
6.5.2. Rezultate numerice118

7. Vartejuri longitudinale contrarotative 128
7.1. Introducere128
7.2. Pereche de vartejuri contrarotative supuse perturbatiilor de tip Crow 129
7.2.1. Domeniul de calcul. Conditii initiale. Conditii la limita 129
7.2.2. Rezultate numerice 131
7.3. Influenta perturbatiilor de tip zgomot alb asupra dipolului turbionar136
7.3.1. Domeniu de calcul. Conditii initiale. Conditii la limita136
7.3.2. Rezultate numerice139
7.4. Influenta turbulentei externe sintetice asupra unui dipol turbionar151
7.4.1. Domeniul de calcul. Conditii initiale. Conditii la limita151
7.4.2. Rezultate numerice152

8. Vartejuri longitudinale contrarotative in prezenta solului 158
8.1. Introducere158
8.2. Interactiunea unei perechi de vartejuri cu solul158
8.2.1. Traiectoriile vartejurilor in prezenta solului158
8.2.2. Generarea de vorticitate in vecinatatea solului162
8.3. Simularea numerica a unei perechi de vartejuri in prezenta solului164
8.3.1. Domeniul de calcul. Conditii initiale. Conditii la limita 164
8.3.2. Rezultate numerice 166

BIBLIOGRAFIE178
  PREZENTARE:
CUVANT INAINTE

O aeronava aflata in zbor conduce la generarea unui siaj turbulent compus din doua sau mai multe perechi de vartejuri contrarotative, intense, orientate in directia zborului. Aceste vartejuri sunt generate de miscarea de rotatie a curentilor de aer la extremitatile suprafetelor portante, datorita diferentei de presiune dintre intrados si extrados. Atunci cand conditiile atmosferice sunt favorabile aparitiei fenomenului de condens sau atunci cand gazele generate de functionarea motoarelor reactive se amesteca cu vartejurile siajului, acestea devin vizibile ca o urma de fum in spatele aeronavei. Intensitatea vartejurilor contrarotative este strict dependenta de greutatea aeronavei, prin urmare o aernava cu dimensiuni mare va produce un siaj cu intensitate importanta. Vartejurile au o durata de viata care poate fi destul de importanta, astfel incat ele pot persista o perioada importanta de timp.

Efectele principale ale siajului asupra unei alte aeronave pot fi: miscarea de ruliu, pierderea de altitudine si generarea de solicitari importante asupra structurii aeronavei. Fenomenul poate deveni extrem de periculos pe timpul fazelor de decolare/aterizare, atunci cand aeronava se deplaseaza la o altitudine mica si nu se mai poate redresa, aeronavele de mici dimensiuni fiind cele mai afectate. Pentru a se evita aparitia accidentelor aeriene provocate de actiunea siajului s-au stabilit o serie de norme nationale si internationale care definesc intervalele de timp minime dintre doua aterizari/decolari, norme care limiteaza destul de mult traficul aerian in zona aeroporturilor.

Cartea prezinta motivatia cercetarilor in domeniul siajului turbulent al aeronavelor, exemple de accidente produse din cauza siajului si o serie de modalitati de diminuare a riscurilor de aparitie a accidentelor in zona aeroporturilor. Se detaliaza aspecte privind procesul de generare a vartejurilor longitudinale contrarotative ce compun siajul aeronavelor si o serie de modele matematice utilizate pentru reprezentarea vartejurilor: modelul Rankine, modelul Lamb-Oseen, modelul Lamb-Chaplygin, precum si un model bazat pe imagini de vartejuri. Se analizeaza doua dintre cele mai importante mecanisme care pot conduce la accelerarea procesului de dezorganizare si de distrugere a siajului turbulent: mecanismele de instabilitate caracterizate de lungime de unda mare (instabilitatea de tip Crow) si mecanismele de instabilitate caracterizate de lungime de unda mica (instabilitatea eliptica). Pentru simularea curgerilor turbulente se utilizeaza metoda Large Eddy Simulation, existand aplicatii pentru studiul unui vartej longitudinal izolat, precum si pentru studiul unei perechi de vartejuri longitudinale contrarotative.

Lucrarea „Modelarea si simularea numerica a siajului turbulent al aeronavelor”, reprezinta un material de referinta pentru personalul tehnico-ingineresc de aviatie, precum si pentru studentii, cadrele didactice si cercetatorii din domeniul inginerie aerospatiala.

Autorul

DESPRE AUTOR:

Cristian-Emil MOLDOVEANU
Dupa absolvirea Academiei Tehnice Militare din Bucuresti in anul 2001, ca ofiter inginer in specializarea Armament, Rachete, Munitii de Aviatie si Sisteme de Salvare, a ocupat pozitiile de sef al laboratorului Sisteme de Armament, asistent universitar, lector universitar, iar ince¬pand cu anul 2011 este conferentiar universitar, predand disciplinele mecanica fluidelor, aerodinamica, balistica exterioara si sisteme de armament de aviatie. In perioada 2004-2007 si-a pregatit teza de doctorat in cadrul Institutului de Mecanica Fluidelor din Toulouse, Franta. Din 2012 este Coordonator Institutional Erasmus, gestionand mobilitati de studenti si de personal universitar desfasurate in peste 40 de universitati partenere din Franta, Spania, Portugalia, Germania, Italia, Belgia, Olanda, Polonia, Republica Ceha, Slovacia si Bulgaria. Activitatea sa stiintifica este concentrata in principal pe subiecte din mecanica fluidelor, aerodinamica si balistica exterioara. Este membru al grupului de lucru NATO STO Modelare si Simulare (NMSG), evaluator ARACIS si evaluator UEFISCDI pentru competitiile nationale de proiecte de cercetare stiintifica, si membru al asociatiilor profesionale AGIR, ISB (Societatea Internationala de Balistica), EAEC (Asociatia Europeana a Coordonatorilor Eramus) si EAIE (Asociatia Europeana pentru Educatie Internationala).
  PREFATA:
PREFACE

The wake of an aircraft is characterized by the presence of at least one counter-rotating intense vortices pair, oriented towards the flight direction and generated by the rotation movement of the air flow, due to the pressure difference between the lower and the upper side of the wing. When the weather conditions are favorable for the occurrence of condensation, or when the gas generated by the aircraft reactive engines interacts with the wake vortices, they become visible as a trail of smoke behind the aircraft. The main effects of the wake turbulence on an aircraft could be the rolling motion, the altitude loss, and the structural load of the aircraft. This phenomenon can turn even more dangerous during the takeoff/landing phases when the aircrafts travel at a low altitude and cannot recover, the small-size aircrafts being the most affected. To prevent the occurrence of aerial accidents caused by the wake’s action, a set of domestic and international rules has been put in place to define the minimum time period between two landings/takeoffs, so that the effect of the first aircraft’s wake doesn’t materially affect the second aircraft. That rules limit the air traffic in the airports area.

This book is a reference material and provides useful modern mathematical and numerical tools for studying, modeling and simulation of the aircraft wake, addressing students, pilots, engineers and researchers in the field of aerospace engineering. The proposed methods are based on an elevated mathematical apparatus and on the use of high-performance computers. The author presents the motivation of the researches in the turbulent wake field, and some examples of aircraft accidents due to wake and some methods for reducing the risks of the accidents in the airport area. He presents aspects regarding the generation of longitudinal counter-rotating vortices and some mathematical models used to represent the vortices: the Rankine, Lamb-Oseen, Lamb-Chaplygin models and a model based on images of vortices. Next, the book focuses on two of the most important mechanisms that can lead to acceleration of disorganization and destruction of turbulent wake: the instability mechanisms characterized by long wavelength (the Crow instability) and the instability mechanisms characterized by short wavelength (elliptical instability). One chapter is dedicated to mathematical models governing the simulation of turbulent flows, the Large Eddy Simulation method being particularly detailed. The author analyzes the behavior of an isolated vortex and its receptivity to external disturbances and presents some methods employed to generate a turbulent field used in the aircraft wake vortices simulations. The book contains the results of simulations of a counter-rotating vortices pair behaviour under the influence of a turbulent atmosphere and near the ground. These simulations reveal the existence of competition between the elliptic and the Crow instability mechanisms.

The author starts the research in the aircraft wake vortices field by a project in the international program FP5 Marie Curie Fellowship, Contract no. HPMT-CT-2000-00079, Waves and Vortices Shear Flows: Instability, Dynamics and Control, at the Institute of Fluid Mechanics from Toulouse during 2003-2004.

The most important part of the results presented in the book was produced during the author`s doctoral research conducted in international Franco-Romanian joint-supervision in the periode 2004 - 2007, under my supervision in collaboration with Andre GIOVANNINI, Institute of Fluid Mechanics of Toulouse and with gl.mr.(r) prof. Florentin MORARU from Military Technical Academy of Bucharest. The results obtained during the doctoral research have been incorporated in the FP6 project no. AST4-CT-2005-012238, Fundamental Research on Aircraft Wake Phenomena - Far-Wake, coordinated by IRPHE Institute of Marseille, project coordinator being professor Thomas LEWEKE, in collaboration with the Institute of Fluid Mechanics from Toulouse. The numerical results presented were obtained using a computational code specialized in incompressible flow simulations, named JADIM, initiated by Jacques MAGNAUDET and Dominique LEGENDRE and developed by a team form CoSINus, Codes et Simulations Numerique from Institute of Fluid Mechanics from Toulouse, under the coordination of Annaig PEDRONO. The numerical simulations were performed using high-performance multiprocessor computing systems in the regional computer center CALMIP Toulouse Midi-Pyrenees.

The book falls within the national and international concerns regarding the study of aircraft turbulent wake vortices. The knowledge map of the aircraft wake vortices field shows certain elements which have been less approached: study of the aircraft wake turbulence generation process, vortex receptivity to atmospheric disturbances, interactions between an aircraft wake vortex and the airport infrastructure elements etc. Some of these outstanding issues in the turbulent aircraft wake vortices field are presented in the chapters of this book. Approaching these elements of international novelty, the book represents an important contribution to the knowledge of the field, thus completing the relevant international knowledge matrix. The scientific area approached by this book is characterized by a wide interdisciplinarity, including fluid mechanics, aerodynamics, aerospace vehicle flight dynamics, numerical methods, computer programming, mathematical statistics, as well as air traffic management.

Institute of Fluid Mechanics from Toulouse
Directeur de Recherche CNRS
Henri-Claude BOISSON
  CUVINTE CHEIE: