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Interactional Aerodynamic Modeling and Analysis of Multi-Rotor Aircraft Using Computational Fluid Dynamics.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Interactional Aerodynamic Modeling and Analysis of Multi-Rotor Aircraft Using Computational Fluid Dynamics./
作者:	Healy, Richard Charles.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2023,
面頁冊數:	413 p.
附註:	Source: Dissertations Abstracts International, Volume: 84-12, Section: B.
Contained By:	Dissertations Abstracts International84-12B.
標題:	Aerospace engineering. -
電子資源:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=30417880
ISBN:	9798379613204

Interactional Aerodynamic Modeling and Analysis of Multi-Rotor Aircraft Using Computational Fluid Dynamics.
Healy, Richard Charles.

Interactional Aerodynamic Modeling and Analysis of Multi-Rotor Aircraft Using Computational Fluid Dynamics. - Ann Arbor : ProQuest Dissertations & Theses, 2023 - 413 p.

Source: Dissertations Abstracts International, Volume: 84-12, Section: B.

Thesis (Ph.D.)--Rensselaer Polytechnic Institute, 2023.

Over the past decade, advancements in battery, electronics, and motor technology have led to the rapid popularization of distributed-electric multicopters. Unlike more traditional turboshaft powered helicopters which use a single rotor for thrust generation and control, electric multicopters employ an array of rotors whose thrust can be individually modulated to stabilize the vehicle. To-date, small-scale multicopters have most commonly been used by hobbyists and videographers; however in recent years attention has turned towards larger multi-rotor electric VTOL (eVTOL) aircraft. These large-scale multicopters can offer many advantages including a quiet noise signature, low mechanical complexity, and low carbon footprint, making them promising for urban air mobility, package delivery, medical transport, and military/law enforcement applications.The distributed-electric propulsion architecture used by eVTOL vehicles allows for flexible placement of multiple lifting and propulsive rotors, leading to a variety of potential advanced configurations. However, when rotors operate in close proximity aerodynamic interactions can lead to degraded (or enhanced) performance. The current batteries powering most eVTOL aircraft exhibit low energy density relative to the hydrocarbon fuels used by conventional VTOL aircraft. Under this limitation, it is especially important to maximize the aerodynamic performance of eVTOL aircraft in order to realize meaningful payload capacity, endurance and range. With this in mind, understanding how rotor-rotor and rotor-wing interactional aerodynamics impact vehicle performance is an important step towards practical eVTOL designs.In this body of work, computational fluid dynamics is used to simulate the aerodynamics of multiple rotors (and wings) operating in close proximity. The Navier Stokes equations are solved using both a stabilized finite element solver with a sliding mesh method as well as a finite volume solver with overset grids. Simulations of numerous multi-rotor/rotor-wing systems are compared to those of isolated rotors and isolated wings operating under the same conditions in order to extract the interactional aerodynamic effects. Through these simulations, the physical mechanisms driving the interactions are established and potentially advantageous designs/configurations are identified.The aerodynamic interactions of two in-line rotors operating in edgewise flight is established and an associated aft-rotor performance penalty is identified. This analysis is extended to systems with varying vertical and longitudinal hub-hub separation where the aft rotor thrust and torque at each separation distance is evaluated. Aft rotor thrust deficit (and torque penalty) is found to be more sensitive to vertical separation than longitudinal spacing.The interactions of in-line rotors are also investigated for when they are canted (and each rotor's rotation axis is tilted). Laterally canted rotors with advancing sides up (and down) are simulated in addition to longitudinally canted inwards (and outwards) rotors. Laterally canting the rotors is found to shift the aft rotor thrust distribution towards the raised side of the disk, thereby significantly modifying the rolling moment but not the thrust generation or torque requirement. Longitudinal canting does however affect the aft rotor thrust, with the canted inward aft rotor generating less thrust than its uncanted counterpart. Canting the rotors outwards reduces the aft rotor thrust deficit, and is found to be the most effective two-rotor configuration, producing a higher equivalent lift to drag ratio than uncanted rotors while also providing enhanced control authority.While much of the existing literature on rotor-rotor interactions pertains to forward flight, close-proximity rotors are also expected to interact when operating close to the ground. Pairs of side-by-side rotors are simulated in ground effect (IGE) at two ground heights and two hub-hub separation distances and their thrust production is compared to that of an isolated rotor out of ground effect (OGE). Between the rotors IGE, colliding wakes generate a region of highly turbulent flow that extends from the ground up to the rotor disks. As blades pass through this turbulent mixing region, unsteady loading is induced and a net thrust deficit is observed. Thrust losses on portions of the disk within the turbulent mixing negate the nominal ground effect thrust increment, particularly when rotors are spaced further apart and close to the ground.Canted side-by-side rotors are also simulated IGE, and their thrust production is compared to uncanted side-by-side rotors at the same height above the ground and hub-hub spacing. Canting the rotors is observed to weaken the ground effect as the wake can more freely convect parallel to the ground and is not reoriented towards the rotor disk. When canted side-by-side rotors are considered, additional inter-rotor turbulent mixing is observed near parts of the disks that are oriented closer to the ground. The thrust deficits incurred by blades passing through this additional turbulence causes all canted rotors IGE to generate less thrust than uncanted side-by-side rotors IGE. If rotor cant is required for improved control authority, laterally canted rotors generate the most thrust IGE whereas canted inwards rotors produce the least.Beyond rotor-rotor interactions, the influence of a rotor operating below and behind a wing is also considered. By simulating the flow and comparing the pressure distribution around an isolated wing to one with the rotor installed, the rotor is seen to introduce a low pressure region that extends over the wing's top surface. The additional rotor-induced suction on the top surface of the wing augments wing lift by up to 134% and provides some stall mitigation at 13° incidence angle. On the rotor, downwash induced by the wing's bound circulation introduces a rotor thrust deficit up to 10% nominal thrust and torque penalty up to 4%. Despite the rotor performance penalties, interactions between the rotor and wing lead to equivalent lift to drag ratio improvements ranging from 47% - 52% over a range of wing angles. As disk loading is increased, the rotor-induced suction strengthens, extending the 66% wing lift increment at 6lb/ft2 up to 115% at 12 lb/ft2 . Flight speeds reanging from 15 kts - 45 kts are also investigated, and wing lift enhancement is found to be strongest at low speeds where rotor suction is strongest relative to the nominal wing surface pressure. Rotor position relative to the wing is also varied, and positioning the rotor below and 2R behind the wing is found to generate the greatest wing lift enhancement. Overall, these results suggest that the interactional aerodynamics associated with mounting a rotor below and behind a wing can introduce enhanced system performance over a range of wing angles, rotor loadings, and flight speeds.Rotor-wing interactions are further investigated for a full vehicle by simulating a modified Quad-Rotor Tail Sitter (modified QRTS) using CFD. The modified QRTS configuration is selected after comprehensive analysis simulations reveal that it requires as little as 72% less power to cruise than an equivalently sized Quadrotor Biplane Tailsitter (QBiT) with fixed pitch rotors. The CFD simulations reveal that in cruise, wing induced downwash on the aft rotors reduces thrust by as much as 33%. However, when the rotors are low-mounted relative to the wing, rotor induced suction enhances wing lift by 2.6%. High-mounting the rotors in contrast alleviates much of the aft rotor thrust deficit but degrades wing performance. Overall, interactional effects on the lift compounded quadcopter tend to cancel, leading to a 3.5% - 7.8% reduction in equivalent lift to drag ratio. When trimmed with CFD-CSD coupling, international aerodoynamic penalties contribute to a reduced 23-27% power reduction over the variable-RPM QBiT compared to the 60% reduction predicted by RCAS.

ISBN: 9798379613204Subjects--Topical Terms:

1002622
Aerospace engineering.
Subjects--Index Terms:

Aerodynamics

Interactional Aerodynamic Modeling and Analysis of Multi-Rotor Aircraft Using Computational Fluid Dynamics.
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520 $a Over the past decade, advancements in battery, electronics, and motor technology have led to the rapid popularization of distributed-electric multicopters. Unlike more traditional turboshaft powered helicopters which use a single rotor for thrust generation and control, electric multicopters employ an array of rotors whose thrust can be individually modulated to stabilize the vehicle. To-date, small-scale multicopters have most commonly been used by hobbyists and videographers; however in recent years attention has turned towards larger multi-rotor electric VTOL (eVTOL) aircraft. These large-scale multicopters can offer many advantages including a quiet noise signature, low mechanical complexity, and low carbon footprint, making them promising for urban air mobility, package delivery, medical transport, and military/law enforcement applications.The distributed-electric propulsion architecture used by eVTOL vehicles allows for flexible placement of multiple lifting and propulsive rotors, leading to a variety of potential advanced configurations. However, when rotors operate in close proximity aerodynamic interactions can lead to degraded (or enhanced) performance. The current batteries powering most eVTOL aircraft exhibit low energy density relative to the hydrocarbon fuels used by conventional VTOL aircraft. Under this limitation, it is especially important to maximize the aerodynamic performance of eVTOL aircraft in order to realize meaningful payload capacity, endurance and range. With this in mind, understanding how rotor-rotor and rotor-wing interactional aerodynamics impact vehicle performance is an important step towards practical eVTOL designs.In this body of work, computational fluid dynamics is used to simulate the aerodynamics of multiple rotors (and wings) operating in close proximity. The Navier Stokes equations are solved using both a stabilized finite element solver with a sliding mesh method as well as a finite volume solver with overset grids. Simulations of numerous multi-rotor/rotor-wing systems are compared to those of isolated rotors and isolated wings operating under the same conditions in order to extract the interactional aerodynamic effects. Through these simulations, the physical mechanisms driving the interactions are established and potentially advantageous designs/configurations are identified.The aerodynamic interactions of two in-line rotors operating in edgewise flight is established and an associated aft-rotor performance penalty is identified. This analysis is extended to systems with varying vertical and longitudinal hub-hub separation where the aft rotor thrust and torque at each separation distance is evaluated. Aft rotor thrust deficit (and torque penalty) is found to be more sensitive to vertical separation than longitudinal spacing.The interactions of in-line rotors are also investigated for when they are canted (and each rotor's rotation axis is tilted). Laterally canted rotors with advancing sides up (and down) are simulated in addition to longitudinally canted inwards (and outwards) rotors. Laterally canting the rotors is found to shift the aft rotor thrust distribution towards the raised side of the disk, thereby significantly modifying the rolling moment but not the thrust generation or torque requirement. Longitudinal canting does however affect the aft rotor thrust, with the canted inward aft rotor generating less thrust than its uncanted counterpart. Canting the rotors outwards reduces the aft rotor thrust deficit, and is found to be the most effective two-rotor configuration, producing a higher equivalent lift to drag ratio than uncanted rotors while also providing enhanced control authority.While much of the existing literature on rotor-rotor interactions pertains to forward flight, close-proximity rotors are also expected to interact when operating close to the ground. Pairs of side-by-side rotors are simulated in ground effect (IGE) at two ground heights and two hub-hub separation distances and their thrust production is compared to that of an isolated rotor out of ground effect (OGE). Between the rotors IGE, colliding wakes generate a region of highly turbulent flow that extends from the ground up to the rotor disks. As blades pass through this turbulent mixing region, unsteady loading is induced and a net thrust deficit is observed. Thrust losses on portions of the disk within the turbulent mixing negate the nominal ground effect thrust increment, particularly when rotors are spaced further apart and close to the ground.Canted side-by-side rotors are also simulated IGE, and their thrust production is compared to uncanted side-by-side rotors at the same height above the ground and hub-hub spacing. Canting the rotors is observed to weaken the ground effect as the wake can more freely convect parallel to the ground and is not reoriented towards the rotor disk. When canted side-by-side rotors are considered, additional inter-rotor turbulent mixing is observed near parts of the disks that are oriented closer to the ground. The thrust deficits incurred by blades passing through this additional turbulence causes all canted rotors IGE to generate less thrust than uncanted side-by-side rotors IGE. If rotor cant is required for improved control authority, laterally canted rotors generate the most thrust IGE whereas canted inwards rotors produce the least.Beyond rotor-rotor interactions, the influence of a rotor operating below and behind a wing is also considered. By simulating the flow and comparing the pressure distribution around an isolated wing to one with the rotor installed, the rotor is seen to introduce a low pressure region that extends over the wing's top surface. The additional rotor-induced suction on the top surface of the wing augments wing lift by up to 134% and provides some stall mitigation at 13° incidence angle. On the rotor, downwash induced by the wing's bound circulation introduces a rotor thrust deficit up to 10% nominal thrust and torque penalty up to 4%. Despite the rotor performance penalties, interactions between the rotor and wing lead to equivalent lift to drag ratio improvements ranging from 47% - 52% over a range of wing angles. As disk loading is increased, the rotor-induced suction strengthens, extending the 66% wing lift increment at 6lb/ft2 up to 115% at 12 lb/ft2 . Flight speeds reanging from 15 kts - 45 kts are also investigated, and wing lift enhancement is found to be strongest at low speeds where rotor suction is strongest relative to the nominal wing surface pressure. Rotor position relative to the wing is also varied, and positioning the rotor below and 2R behind the wing is found to generate the greatest wing lift enhancement. Overall, these results suggest that the interactional aerodynamics associated with mounting a rotor below and behind a wing can introduce enhanced system performance over a range of wing angles, rotor loadings, and flight speeds.Rotor-wing interactions are further investigated for a full vehicle by simulating a modified Quad-Rotor Tail Sitter (modified QRTS) using CFD. The modified QRTS configuration is selected after comprehensive analysis simulations reveal that it requires as little as 72% less power to cruise than an equivalently sized Quadrotor Biplane Tailsitter (QBiT) with fixed pitch rotors. The CFD simulations reveal that in cruise, wing induced downwash on the aft rotors reduces thrust by as much as 33%. However, when the rotors are low-mounted relative to the wing, rotor induced suction enhances wing lift by 2.6%. High-mounting the rotors in contrast alleviates much of the aft rotor thrust deficit but degrades wing performance. Overall, interactional effects on the lift compounded quadcopter tend to cancel, leading to a 3.5% - 7.8% reduction in equivalent lift to drag ratio. When trimmed with CFD-CSD coupling, international aerodoynamic penalties contribute to a reduced 23-27% power reduction over the variable-RPM QBiT compared to the 60% reduction predicted by RCAS.
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