Tiltrotor aircraft are challenging machines to design considering the various operating conditions and multipurpose missions that are expected to be performed by this complex type of aircraft. This machine combines the characteristic of a conventional turboprop aircraft with the vertical take-off and landing (VTOL) capability of a helicopter. In the past, some catastrophic accidents involved tiltrotors, which were caused by a combination of factors: complex three-dimensional unsteady aerodynamic flow field, structural loads, aeroelastic instabilities, and pilot control inputs. Therefore, the development of a comprehensive tool capable of capturing the combination of all these phenomena is of paramount importance for designing faster, lighter, and safer tiltrotors. The main objective of this work is to develop, validate, and evaluate the limits of aeroelastic and aeromechanical stability of a tiltrotor aircraft using a comprehensive approach in mid-fidelity. Thanks to a large amount of freely available data, the Bell XV-15 tiltrotor equipped with Advanced Technology Blades (ATB) is chosen as a representative model; however, due to the modularity and parameterization of the model, other innovative rotary-wing configurations could be studied with the proposed approach. The model is built using a co-simulation approach based on the coupling between a mid-fidelity aerodynamic solver based on the vortex particle method for wake modeling, DUST, and the multibody dynamics code, MBDyn. This coupling is managed through the partitioned multiphysics coupling library preCICE. In the first part of the work, the coupled tool is presented and validated by solving simple fixed-wing and rotary-wing problems from the open literature. In the second part, the multibody and aerodynamic modeling of each subcomponent, using the open-source software MBDyn and DUST, is illustrated and validated considering experimental and numerical results. Each subcomponent is extensively validated against the available results and, starting from these, they are extended to enable the validation with other analytical tools. Globally, a good correlation is reached in the dynamics analyses for the whole system. In particular, the coupled model shows great advantages in terms of computational time and accuracy concerning high-fidelity tools when used to estimate hover performance. A time-marching trim procedure is also proposed, and optimal longitudinal control of the tiltrotor is presented and validated to maintain altitude. A detailed multibody biomechanical model of the upper body of a generic pilot is presented. It is made up of connecting a previously developed detailed model of the arms to a similarly detailed model of the spine. The entire model can be adapted to a specific subject identified by age, sex, weight, and height. The spine model and the scaling procedure are validated using experimental results for seat-to-head transmissibility. The coupled spine-arms model is used to evaluate the biodynamic response in terms of involuntary motion induced in the control inceptors, including related non-linearities. Finally, the tiltrotor and pilot models are combined into a single comprehensive model in which the whirl flutter aeroelastic stability is investigated over the entire flight envelope, and the responses to discrete gusts were used to evaluate the effect of the pilot biomechanics and interactional aerodynamics. The results show that including an unsteady aerodynamic model is of paramount importance, especially when dealing with flight dynamics modes. This model enables a wide spectrum of different analyses: for example, this model will be used to study passenger comfort, and performance in transient maneuvers such as conversion and pull-up, aeroelastic stability, pilot-induced-oscillation, and pilot-augmented-oscillation phenomena. The coupled multibody-mid-fidelity tool can be used for performing the large number of aeroelastic analyses required in the preliminary design phase of innovative rotary-wing configurations, not only in the rotorcraft field but also in other domains, from wind energy to micro-aerial vehicles.
I convertiplani sono macchine impegnative da progettare considerando le varie condizioni operative e le missioni polivalenti che dovrebbero essere eseguite da questo complesso tipo di velivolo. Questa macchina combina le caratteristiche di un velivolo a turboelica convenzionale con la capacità di decollo e atterraggio verticale di un elicottero. In passato, alcuni incidenti catastrofici hanno coinvolto i convertiplani, causati da una combinazione di fattori: campo di flusso aerodinamico instabile tridimensionale, carichi strutturali, instabilità aeroelastiche e input di controllo del pilota. Pertanto, lo sviluppo di uno strumento completo in grado di catturare la combinazione di tutti questi fenomeni è di fondamentale importanza per progettare convertiplani più veloci, leggeri e sicuri. L'obiettivo principale di questo lavoro è quello di sviluppare, convalidare e valutare i limiti di stabilità aeroelastica e aeromeccanica di un velivolo convertiplano utilizzando un approccio globale a media fedeltà. Grazie alla grande quantità di dati liberamente disponibili, il convertiplano Bell XV-15 dotato di Advanced Technology Blades (ATB) viene scelto come modello rappresentativo; tuttavia, data la modularità e la parametrizzazione del modello, potrebbero essere studiate altre configurazioni innovative ad ala rotante con l'approccio proposto. Il modello è costruito utilizzando un approccio di co-simulazione basato sull'accoppiamento tra un risolutore aerodinamico di media fedeltà basato sul metodo delle particelle vorticose per la modellazione della scia, DUST e la dinamica multicorpo codice MBDyn. Questo accoppiamento è gestito attraverso la libreria di accoppiamento multifisico preCICE. Nella prima parte del lavoro, lo strumento accoppiato viene presentato e validato risolvendo semplici problemi ad ala fissa e ad ala rotante presenti in letteratura. Nella seconda parte, viene illustrata e validata la modellazione multicorpo e aerodinamica di ciascun sottocomponente, utilizzando il software open-source MBDyn e DUST, considerando i risultati sperimentali e numerici. Ogni sottocomponente è ampiamente validato rispetto ai risultati disponibili e, a partire da questi, vengono estesi per consentire la validazione con altri strumenti analitici. A livello globale, si raggiunge una buona correlazione nelle analisi dinamiche per l'intero sistema. In particolare, il modello accoppiato mostra grandi vantaggi in termini di tempo computazionale e accuratezza rispetto agli strumenti ad alta fedeltà quando utilizzato per stimare le prestazioni di volo stazionario. Viene inoltre proposta una procedura per l'ottenimento dell'assetto mediante una simulazione integrata nel tempo e viene presentato e convalidato il controllo longitudinale ottimale del convertiplano per mantenere l'altitudine. Da ultimo, viene presentato un modello biomeccanico multicorpo dettagliato della parte superiore del corpo di un pilota generico. Consiste nel collegare un modello dettagliato delle braccia sviluppato in precedenza a un modello altrettanto dettagliato della colonna vertebrale. L'intero modello può essere adattato a un soggetto specifico individuato per età, sesso, peso e altezza. Il modello della colonna vertebrale e la procedura di ridimensionamento sono convalidati utilizzando risultati sperimentali per la trasmissibilità sedile-testa. Il modello accoppiato colonna vertebrale-braccia viene utilizzato per valutare la risposta biodinamica in termini di movimento involontario indotto negli incettori di controllo, comprese le relative non linearità. Infine, i modelli del convertiplano e del pilota sono combinati in un unico modello completo in cui la stabilità aeroelastica a whirl-flutter viene studiata sull'intero inviluppo di volo e le risposte a raffiche discrete sono state utilizzate per valutare l'effetto della biomeccanica del pilota e dell'aerodinamica interazionale. I risultati mostrano che l'inclusione di un modello aerodinamico instabile è di fondamentale importanza, specialmente quando si ha a che fare con le modalità dinamiche di volo. Questo modello consente un ampio spettro di analisi diverse: ad esempio, questo modello verrà utilizzato per studiare il comfort dei passeggeri e le prestazioni in manovre transitorie come la conversione e il pull-up, la stabilità aeroelastica, l'oscillazione indotta dal pilota e l'aumento del pilota fenomeni di oscillazione. Lo strumento accoppiato multibody-mid-fidelity può essere utilizzato per eseguire il gran numero di analisi aeroelastiche richieste nella fase di progettazione preliminare di configurazioni innovative ad ala rotante, non solo nel campo degli elicotteri ma anche in altri domini, dall'energia eolica alla micro-veicoli aerei.
Comprehensive mid-fidelity simulation environment for aeroelastic stability analysis of tiltrotors with pilot-in-the-loop
Cocco, Alessandro
2022/2023
Abstract
Tiltrotor aircraft are challenging machines to design considering the various operating conditions and multipurpose missions that are expected to be performed by this complex type of aircraft. This machine combines the characteristic of a conventional turboprop aircraft with the vertical take-off and landing (VTOL) capability of a helicopter. In the past, some catastrophic accidents involved tiltrotors, which were caused by a combination of factors: complex three-dimensional unsteady aerodynamic flow field, structural loads, aeroelastic instabilities, and pilot control inputs. Therefore, the development of a comprehensive tool capable of capturing the combination of all these phenomena is of paramount importance for designing faster, lighter, and safer tiltrotors. The main objective of this work is to develop, validate, and evaluate the limits of aeroelastic and aeromechanical stability of a tiltrotor aircraft using a comprehensive approach in mid-fidelity. Thanks to a large amount of freely available data, the Bell XV-15 tiltrotor equipped with Advanced Technology Blades (ATB) is chosen as a representative model; however, due to the modularity and parameterization of the model, other innovative rotary-wing configurations could be studied with the proposed approach. The model is built using a co-simulation approach based on the coupling between a mid-fidelity aerodynamic solver based on the vortex particle method for wake modeling, DUST, and the multibody dynamics code, MBDyn. This coupling is managed through the partitioned multiphysics coupling library preCICE. In the first part of the work, the coupled tool is presented and validated by solving simple fixed-wing and rotary-wing problems from the open literature. In the second part, the multibody and aerodynamic modeling of each subcomponent, using the open-source software MBDyn and DUST, is illustrated and validated considering experimental and numerical results. Each subcomponent is extensively validated against the available results and, starting from these, they are extended to enable the validation with other analytical tools. Globally, a good correlation is reached in the dynamics analyses for the whole system. In particular, the coupled model shows great advantages in terms of computational time and accuracy concerning high-fidelity tools when used to estimate hover performance. A time-marching trim procedure is also proposed, and optimal longitudinal control of the tiltrotor is presented and validated to maintain altitude. A detailed multibody biomechanical model of the upper body of a generic pilot is presented. It is made up of connecting a previously developed detailed model of the arms to a similarly detailed model of the spine. The entire model can be adapted to a specific subject identified by age, sex, weight, and height. The spine model and the scaling procedure are validated using experimental results for seat-to-head transmissibility. The coupled spine-arms model is used to evaluate the biodynamic response in terms of involuntary motion induced in the control inceptors, including related non-linearities. Finally, the tiltrotor and pilot models are combined into a single comprehensive model in which the whirl flutter aeroelastic stability is investigated over the entire flight envelope, and the responses to discrete gusts were used to evaluate the effect of the pilot biomechanics and interactional aerodynamics. The results show that including an unsteady aerodynamic model is of paramount importance, especially when dealing with flight dynamics modes. This model enables a wide spectrum of different analyses: for example, this model will be used to study passenger comfort, and performance in transient maneuvers such as conversion and pull-up, aeroelastic stability, pilot-induced-oscillation, and pilot-augmented-oscillation phenomena. The coupled multibody-mid-fidelity tool can be used for performing the large number of aeroelastic analyses required in the preliminary design phase of innovative rotary-wing configurations, not only in the rotorcraft field but also in other domains, from wind energy to micro-aerial vehicles.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/195753