Aerospace

3972 KiB

Open AccessArticle

Improved Separation of Tone and Broadband Noise Components from Open Rotor Acoustic Data

by Dave Sree and David B. Stephens

Aerospace 2016, 3(3), 29; https://doi.org/10.3390/aerospace3030029 - 20 Sep 2016

Cited by 13 | Viewed by 8420

The term “open rotor” refers to unducted counter-rotating dual rotors or propellers used for propulsion. The noise generated by an open rotor is very complicated and requires special techniques for its analysis. The determination of its tone and broadband components is vital for [...] Read more.

The term “open rotor” refers to unducted counter-rotating dual rotors or propellers used for propulsion. The noise generated by an open rotor is very complicated and requires special techniques for its analysis. The determination of its tone and broadband components is vital for properly assessing the noise control parameters and also for validating open rotor noise prediction codes. The data analysis technique developed by Sree for processing raw acoustic data of open rotors has been modified to yield much better results of tone and broadband separation particularly for the case when the two rotor speeds are approximately the same. The modified algorithm is found to eliminate most or all of the “spikes” previously observed in the broadband spectra computed from the original algorithm. A full description of the modified algorithm and examples of improved results from its application are presented in this paper. Full article

(This article belongs to the Special Issue Recent Advances in Aeroacoustics)

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8934 KiB

Open AccessArticle

An Implementation of Real-Time Phased Array Radar Fundamental Functions on a DSP-Focused, High-Performance, Embedded Computing Platform

by Xining Yu, Yan Zhang, Ankit Patel, Allen Zahrai and Mark Weber

Aerospace 2016, 3(3), 28; https://doi.org/10.3390/aerospace3030028 - 09 Sep 2016

Cited by 7 | Viewed by 9279

Abstract

This paper investigates the feasibility of a backend design for real-time, multiple-channel processing digital phased array system, particularly for high-performance embedded computing platforms constructed of general purpose digital signal processors. First, we obtained the lab-scale backend performance benchmark from simulating beamforming, pulse compression, [...] Read more.

This paper investigates the feasibility of a backend design for real-time, multiple-channel processing digital phased array system, particularly for high-performance embedded computing platforms constructed of general purpose digital signal processors. First, we obtained the lab-scale backend performance benchmark from simulating beamforming, pulse compression, and Doppler filtering based on a Micro Telecom Computing Architecture (MTCA) chassis using the Serial RapidIO protocol in backplane communication. Next, a field-scale demonstrator of a multifunctional phased array radar is emulated by using the similar configuration. Interestingly, the performance of a barebones design is compared to that of emerging tools that systematically take advantage of parallelism and multicore capabilities, including the Open Computing Language. Full article

(This article belongs to the Special Issue Radar and Aerospace)

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1117 KiB

Open AccessArticle

Aerodynamic Modeling of NREL 5-MW Wind Turbine for Nonlinear Control System Design: A Case Study Based on Real-Time Nonlinear Receding Horizon Control

by Pedro A. Galvani, Fei Sun and Kamran Turkoglu

Aerospace 2016, 3(3), 27; https://doi.org/10.3390/aerospace3030027 - 30 Aug 2016

Cited by 11 | Viewed by 9588

Abstract

The work presented in this paper has two major aspects: (i) investigation of a simple, yet efficient model of the NREL (National Renewable Energy Laboratory) 5-MW reference wind turbine; (ii) nonlinear control system development through a real-time nonlinear receding horizon control methodology with [...] Read more.

The work presented in this paper has two major aspects: (i) investigation of a simple, yet efficient model of the NREL (National Renewable Energy Laboratory) 5-MW reference wind turbine; (ii) nonlinear control system development through a real-time nonlinear receding horizon control methodology with application to wind turbine control dynamics. In this paper, the results of our simple wind turbine model and a real-time nonlinear control system implementation are shown in comparison with conventional control methods. For this purpose, the wind turbine control problem is converted into an optimization problem and is directly solved by the nonlinear backwards sweep Riccati method to generate the control protocol, which results in a non-iterative algorithm. One main contribution of this paper is that we provide evidence through simulations, that such an advanced control strategy can be used for real-time control of wind turbine dynamics. Examples are provided to validate and demonstrate the effectiveness of the presented scheme. Full article

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9604 KiB

Open AccessArticle

Optimization of a Human-Powered Aircraft Using Fluid–Structure Interaction Simulations

by Bob Vanderhoydonck, Gilberto Santo, Jan Vierendeels and Joris Degroote

Aerospace 2016, 3(3), 26; https://doi.org/10.3390/aerospace3030026 - 26 Aug 2016

Cited by 5 | Viewed by 11442

Abstract

The special type of aircrafts in which the human power of the pilot is sufficient to take off and sustain flight are known as Human-Powered Aircrafts (HPAs). To explore the peculiarities of these aircrafts, the aerodynamic performance of an existing design is evaluated [...] Read more.

The special type of aircrafts in which the human power of the pilot is sufficient to take off and sustain flight are known as Human-Powered Aircrafts (HPAs). To explore the peculiarities of these aircrafts, the aerodynamic performance of an existing design is evaluated first, using both the vortex lattice method and computational fluid dynamics. In a second step, it is attempted to design and optimize a new HPA capable of winning the Kremer International Marathon Competition. The design will be special in that it allows one to include a second pilot on board the aircraft. As the structural deflection of the wing is found to be a key aspect during design, fluid–structure interaction simulations are performed and included in the optimization procedure. To assess the feasibility of winning the competition, the physical performance of candidate pilots is measured and compared with the predicted required power. Full article

(This article belongs to the Special Issue Fluid-Structure Interactions)

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5215 KiB

Open AccessArticle

Effect of the Backward-Facing Step Location on the Aerodynamics of a Morphing Wing

by Fadi Mishriky and Paul Walsh

Aerospace 2016, 3(3), 25; https://doi.org/10.3390/aerospace3030025 - 11 Aug 2016

Cited by 9 | Viewed by 12387

Abstract

Over the last decade, aircraft morphing technology has drawn a lot of attention in the aerospace community, because it is likely to improve the aerodynamic performance and the versatility of aircraft at different flight regimes. With the fast paced advancements in this field, [...] Read more.

Over the last decade, aircraft morphing technology has drawn a lot of attention in the aerospace community, because it is likely to improve the aerodynamic performance and the versatility of aircraft at different flight regimes. With the fast paced advancements in this field, a parallel stream of research is studying different materials and designs to develop reliable morphing skins. A promising candidate for a viable morphing skin is the sliding skin, where two or more rigid surfaces remain in contact and slide against each other during morphing. The overlapping between each two panels create a backward-facing step on the airfoil surface which has a critical effect on the aerodynamics of the wing. This paper presents a numerical study of the effect of employing a backward-facing step on the suction side of a National Advisory Committee for Aeronautics (NACA) 2412 airfoil at a high Reynolds number of 5.9 × 10⁶. The effects of the step location on the lift coefficient, drag coefficient and critical angle of attack are studied to find a favorable location for the step along the chord-wise direction. Results showed that employing a step on the suction side of the NACA 2412 airfoil can adversely affect the aforementioned aerodynamic properties. A drop of 21.1% in value of the lift coefficient and an increase of 120.8% in the drag coefficient were observed in case of a step located at 25% of the chord length. However, these effects are mitigated by shifting the step location towards the trailing edge. Introducing a step on the airfoil caused the airfoil’s thickness to change, which in turn has affected the transition point of the viscous boundary layer from laminar to turbulent. The location of the step, prior or post the transition point, has a noteworthy effect on the pressure and shear stress distribution, and consequently on the values of the lift and drag coefficients. Full article

(This article belongs to the Special Issue Adaptive/Smart Structures and Multifunctional Materials 2016)

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1145 KiB

Open AccessArticle

Comparison of the Average Lift Coefficient ͞C_L and Normalized Lift ͞η_L for Evaluating Hovering and Forward Flapping Flight

by Phillip Burgers

Aerospace 2016, 3(3), 24; https://doi.org/10.3390/aerospace3030024 - 29 Jul 2016

Cited by 3 | Viewed by 6941

Abstract

The capability of flapping wings to generate lift is currently evaluated by using the lift coefficient

{\bar{C}}_{L}

, a dimensionless number that is derived from the basal equation that calculates the steady-state lift coefficient C_L for fixed wings. In contrast [...] Read more.

The capability of flapping wings to generate lift is currently evaluated by using the lift coefficient

{\bar{C}}_{L}

, a dimensionless number that is derived from the basal equation that calculates the steady-state lift coefficient C_L for fixed wings. In contrast to its simple and direct application to fixed wings, the equation for

{\bar{C}}_{L}

requires prior knowledge of the flow field along the wing span, which results in two integrations: along the wing span and over time. This paper proposes an alternate average normalized lift

{\bar{η}}_{L}

that is easy to apply to hovering and forward flapping flight, does not require prior knowledge of the flow field, does not resort to calculus for its solution, and its lineage is close to the basal equation for steady state C_L. Furthermore, the average normalized lift

{\bar{η}}_{L}

converges to the legacy C_L as the flapping frequency is reduced to zero (gliding flight). Its ease of use is illustrated by applying the average normalized lift

{\bar{η}}_{L}

to the hovering and translating flapping flight of bumblebees. This application of the normalized lift is compared to the same application using two widely-accepted legacy average lift coefficients: the first

{\bar{C}}_{L}

as defined by Dudley and Ellington, and the second lift coefficient by Weis-Fogh. Furthermore, it is shown that the average normalized lift

{\bar{η}}_{L}

has a physical meaning: that of the ratio of work exerted by the flapping wings onto the surrounding flow field and the kinetic energy available at the aerodynamic surfaces during the generation of lift. The working equation for the average normalized lift

{\bar{η}}_{L}

is derived and is presented as a function of Strouhal number, St. Full article

(This article belongs to the Special Issue Flapping Wings)

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6973 KiB

Open AccessArticle

Analysis of Kinematics of Flapping Wing UAV Using OptiTrack Systems

by Matthew Ng Rongfa, Teppatat Pantuphag and Sutthiphong Srigrarom

Aerospace 2016, 3(3), 23; https://doi.org/10.3390/aerospace3030023 - 26 Jul 2016

Cited by 13 | Viewed by 12470

Abstract

An analysis of the kinematics of a flapping membrane wing using experimental kinematic data is presented. This motion capture technique tracks the positon of the retroreflective marker(s) placed on the left wing of a 1.3-m-wingspan ornithopter. The time-varying three-dimensional data of the wing [...] Read more.

An analysis of the kinematics of a flapping membrane wing using experimental kinematic data is presented. This motion capture technique tracks the positon of the retroreflective marker(s) placed on the left wing of a 1.3-m-wingspan ornithopter. The time-varying three-dimensional data of the wing kinematics were recorded for a single frequency. The wing shape data was then plotted on a two-dimensional plane to understand the wing dynamic behaviour of an ornithopter. Specifically, the wing tip path, leading edge bending, wing membrane shape, local twist, stroke angle and wing velocity were analyzed. As the three characteristic angles can be expressed in the Fourier series as a function of time, the kinematics of the wing can be computationally generated for the aerodynamic study of flapping flight through the Fourier coefficients presented. Analysis of the ornithopter wing showed how the ornithopter closely mimics the flight motions of birds despite several physical limitations. Full article

(This article belongs to the Special Issue Flapping Wings)

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2387 KiB

Open AccessFeature PaperCommunication

Exploring Civil Drone Accidents and Incidents to Help Prevent Potential Air Disasters

by Graham Wild, John Murray and Glenn Baxter

Aerospace 2016, 3(3), 22; https://doi.org/10.3390/aerospace3030022 - 22 Jul 2016

Cited by 115 | Viewed by 22809

Abstract

A recent alleged “drone” collision with a British Airways Airbus A320 at Heathrow Airport highlighted the need to understand civil Remotely Piloted Aircraft Systems (RPAS) accidents and incidents (events). This understanding will facilitate improvements in safety by ensuring efforts are focused to reduce [...] Read more.

A recent alleged “drone” collision with a British Airways Airbus A320 at Heathrow Airport highlighted the need to understand civil Remotely Piloted Aircraft Systems (RPAS) accidents and incidents (events). This understanding will facilitate improvements in safety by ensuring efforts are focused to reduce the greatest risks. One hundred and fifty two RPAS events were analyzed. The data was collected from a 10-year period (2006 to 2015). Results show that, in contrast to commercial air transportation (CAT), RPAS events have a significantly different distribution when categorized by occurrence type, phase of flight, and safety issue. Specifically, it was found that RPAS operations are more likely to experience (1) loss of control in-flight, (2) events during takeoff and in cruise, and (3) equipment problems. It was shown that technology issues, not human factors, are the key contributor in RPAS events. This is a significant finding, as it is contrary to the industry view which has held for the past quarter of a century that human factors are the key contributor (which is still the case for CAT). Regulators should therefore look at technologies and not focus solely on operators. Full article

(This article belongs to the Special Issue Feature Papers in Aerospace)

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10800 KiB

Open AccessFeature PaperReview

Bio-Inspired Principles Applied to the Guidance, Navigation and Control of UAS

by Reuben Strydom, Aymeric Denuelle and Mandyam V. Srinivasan

Aerospace 2016, 3(3), 21; https://doi.org/10.3390/aerospace3030021 - 20 Jul 2016

Cited by 13 | Viewed by 12620

Abstract

This review describes a number of biologically inspired principles that have been applied to the visual guidance, navigation and control of Unmanned Aerial System (UAS). The current limitations of UAS systems are outlined, such as the over-reliance on GPS, the requirement for more [...] Read more.

This review describes a number of biologically inspired principles that have been applied to the visual guidance, navigation and control of Unmanned Aerial System (UAS). The current limitations of UAS systems are outlined, such as the over-reliance on GPS, the requirement for more self-reliant systems and the need for UAS to have a greater understanding of their environment. It is evident that insects, even with their small brains and limited intelligence, have overcome many of the shortcomings of the current state of the art in autonomous aerial guidance. This has motivated research into bio-inspired systems and algorithms, specifically vision-based navigation, situational awareness and guidance. Full article

(This article belongs to the Collection Unmanned Aerial Systems)

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10429 KiB

Open AccessArticle

Hydrodynamic Performance of Aquatic Flapping: Efficiency of Underwater Flight in the Manta

by Frank E. Fish, Christian M. Schreiber, Keith W. Moored, Geng Liu, Haibo Dong and Hilary Bart-Smith

Aerospace 2016, 3(3), 20; https://doi.org/10.3390/aerospace3030020 - 11 Jul 2016

Cited by 119 | Viewed by 22672

Abstract

The manta is the largest marine organism to swim by dorsoventral oscillation (flapping) of the pectoral fins. The manta has been considered to swim with a high efficiency stroke, but this assertion has not been previously examined. The oscillatory swimming strokes of the [...] Read more.

The manta is the largest marine organism to swim by dorsoventral oscillation (flapping) of the pectoral fins. The manta has been considered to swim with a high efficiency stroke, but this assertion has not been previously examined. The oscillatory swimming strokes of the manta were examined by detailing the kinematics of the pectoral fin movements swimming over a range of speeds and by analyzing simulations based on computational fluid dynamic potential flow and viscous models. These analyses showed that the fin movements are asymmetrical up- and downstrokes with both spanwise and chordwise waves interposed into the flapping motions. These motions produce complex three-dimensional flow patterns. The net thrust for propulsion was produced from the distal half of the fins. The vortex flow pattern and high propulsive efficiency of 89% were associated with Strouhal numbers within the optimal range (0.2–0.4) for rays swimming at routine and high speeds. Analysis of the swimming pattern of the manta provided a baseline for creation of a bio-inspired underwater vehicle, MantaBot. Full article

(This article belongs to the Special Issue Flapping Wings)

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19338 KiB

Open AccessArticle

The Efficiency of a Hybrid Flapping Wing Structure—A Theoretical Model Experimentally Verified

by Yuval Keren, Haim Abramovich and Rimon Arieli

Aerospace 2016, 3(3), 19; https://doi.org/10.3390/aerospace3030019 - 05 Jul 2016

Cited by 1 | Viewed by 8466

Abstract

To propel a lightweight structure, a hybrid wing structure was designed; the wing’s geometry resembled a rotor blade, and its flexibility resembled an insect’s flapping wing. The wing was designed to be flexible in twist and spanwise rigid, thus maintaining the aeroelastic advantages [...] Read more.

To propel a lightweight structure, a hybrid wing structure was designed; the wing’s geometry resembled a rotor blade, and its flexibility resembled an insect’s flapping wing. The wing was designed to be flexible in twist and spanwise rigid, thus maintaining the aeroelastic advantages of a flexible wing. The use of a relatively “thick” airfoil enabled the achievement of higher strength to weight ratio by increasing the wing’s moment of inertia. The optimal design was based on a simplified quasi-steady inviscid mathematical model that approximately resembles the aerodynamic and inertial behavior of the flapping wing. A flapping mechanism that imitates the insects’ flapping pattern was designed and manufactured, and a set of experiments for various parameters was performed. The simplified analytical model was updated according to the tests results, compensating for the viscid increase of drag and decrease of lift, that were neglected in the simplified calculations. The propelling efficiency of the hovering wing at various design parameters was calculated using the updated model. It was further validated by testing a smaller wing flapping at a higher frequency. Good and consistent test results were obtained in line with the updated model, yielding a simple, yet accurate tool, for flapping wings design. Full article

(This article belongs to the Special Issue Flapping Wings)

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2849 KiB

Open AccessArticle

Large Scale Applications Using FBG Sensors: Determination of In-Flight Loads and Shape of a Composite Aircraft Wing

by Matthew J. Nicolas, Rani W. Sullivan and W. Lance Richards

Aerospace 2016, 3(3), 18; https://doi.org/10.3390/aerospace3030018 - 23 Jun 2016

Cited by 98 | Viewed by 13284

Abstract

Technological advances have enabled the development of a number of optical fiber sensing methods over the last few years. The most prevalent optical technique involves the use of fiber Bragg grating (FBG) sensors. These small, lightweight sensors have many attributes that enable their [...] Read more.

Technological advances have enabled the development of a number of optical fiber sensing methods over the last few years. The most prevalent optical technique involves the use of fiber Bragg grating (FBG) sensors. These small, lightweight sensors have many attributes that enable their use for a number of measurement applications. Although much literature is available regarding the use of FBGs for laboratory level testing, few publications in the public domain exist of their use at the operational level. Therefore, this paper gives an overview of the implementation of FBG sensors for large scale structures and applications. For demonstration, a case study is presented in which FBGs were used to determine the deflected wing shape and the out-of-plane loads of a 5.5-m carbon-composite wing of an ultralight aerial vehicle. The in-plane strains from the 780 FBG sensors were used to obtain the out-of-plane loads as well as the wing shape at various load levels. The calculated out-of-plane displacements and loads were within 4.2% of the measured data. This study demonstrates a practical method in which direct measurements are used to obtain critical parameters from the high distribution of FBG sensors. This procedure can be used to obtain information for structural health monitoring applications to quantify healthy vs. unhealthy structures. Full article

(This article belongs to the Special Issue Adaptive/Smart Structures and Multifunctional Materials 2016)

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Aerospace, Volume 3, Issue 3 (September 2016) – 12 articles

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