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  Subjects -> AERONAUTICS AND SPACE FLIGHT (Total: 87 journals)
Acta Astronautica     Hybrid Journal   (Followers: 305)
Advances in Space Research     Full-text available via subscription   (Followers: 311)
Aeronautica     Open Access   (Followers: 5)
Aerospace     Open Access   (Followers: 4)
Aerospace and Electronic Systems, IEEE Transactions on     Hybrid Journal   (Followers: 56)
Aerospace Science and Technology     Hybrid Journal   (Followers: 317)
Affective Computing, IEEE Transactions on     Hybrid Journal   (Followers: 8)
AIAA Journal     Full-text available via subscription   (Followers: 510)
Air Force Magazine     Full-text available via subscription   (Followers: 3)
Air Medical Journal     Hybrid Journal   (Followers: 2)
Aircraft Engineering and Aerospace Technology     Hybrid Journal   (Followers: 137)
American Journal of Space Science     Open Access   (Followers: 35)
Artificial Satellites     Open Access   (Followers: 14)
Aviation     Hybrid Journal   (Followers: 3)
Aviation in Focus - Journal of Aeronautical Sciences     Open Access   (Followers: 1)
Aviation Psychology and Applied Human Factors     Hybrid Journal   (Followers: 5)
Aviation Week     Full-text available via subscription   (Followers: 10)
Aviation, Space, and Environmental Medicine     Full-text available via subscription   (Followers: 5)
Canadian Aeronautics and Space Journal     Full-text available via subscription   (Followers: 13)
CEAS Aeronautical Journal     Hybrid Journal   (Followers: 21)
Chinese Journal of Aeronautics     Open Access   (Followers: 11)
Control Systems     Hybrid Journal   (Followers: 19)
Cosmic Research     Hybrid Journal   (Followers: 2)
COSPAR Colloquia Series     Full-text available via subscription   (Followers: 1)
Egyptian Journal of Remote Sensing and Space Science     Open Access   (Followers: 5)
Elsevier Astrodynamics Series     Full-text available via subscription   (Followers: 1)
Fatigue of Aircraft Structures     Open Access   (Followers: 4)
Frontiers in Aerospace Engineering     Open Access   (Followers: 4)
Gyroscopy and Navigation     Hybrid Journal   (Followers: 12)
IEEE Aerospace and Electronic Systems Magazine     Full-text available via subscription   (Followers: 35)
IEEE Transactions on Circuits and Systems I: Regular Papers     Hybrid Journal   (Followers: 9)
International Journal of Aeroacoustics     Full-text available via subscription   (Followers: 6)
International Journal of Aerodynamics     Hybrid Journal   (Followers: 11)
International Journal of Aerospace Engineering     Open Access   (Followers: 42)
International Journal of Aerospace Innovations     Full-text available via subscription   (Followers: 11)
International Journal of Applied Geospatial Research     Full-text available via subscription   (Followers: 4)
International Journal of Aviation Management     Hybrid Journal  
International Journal of Aviation Psychology     Hybrid Journal   (Followers: 4)
International Journal of Aviation Technology, Engineering and Management     Full-text available via subscription  
International Journal of Crashworthiness     Hybrid Journal   (Followers: 5)
International Journal of Flow Control     Full-text available via subscription   (Followers: 2)
International Journal of Hypersonics     Full-text available via subscription   (Followers: 3)
International Journal of Micro Air Vehicles     Full-text available via subscription   (Followers: 3)
International Journal of Satellite Communications Policy and Management     Hybrid Journal  
International Journal of Space Science and Engineering     Hybrid Journal   (Followers: 2)
International Journal of Space Structures     Full-text available via subscription   (Followers: 2)
International Journal of Sustainable Aviation     Hybrid Journal  
International Journal of Turbo & Jet-Engines     Full-text available via subscription  
ISRN Astronomy and Astrophysics     Open Access   (Followers: 11)
Journal of Aerospace Computing, Information, and Communication     Full-text available via subscription   (Followers: 12)
Journal of Aerospace Engineering     Full-text available via subscription   (Followers: 131)
Journal of Aerospace Engineering & Technology     Full-text available via subscription  
Journal of Aerospace Operations     Hybrid Journal   (Followers: 3)
Journal of Aerospace Technology and Management     Open Access   (Followers: 1)
Journal of Aircraft     Full-text available via subscription   (Followers: 286)
Journal of Airline and Airport Management     Open Access   (Followers: 2)
Journal of Aviation Technology and Engineering     Open Access   (Followers: 6)
Journal of Guidance, Control, and Dynamics     Full-text available via subscription   (Followers: 52)
Journal of Konbin     Open Access  
Journal of Navigation     Hybrid Journal   (Followers: 19)
Journal of Propulsion and Power     Full-text available via subscription   (Followers: 238)
Journal of Space Weather and Space Climate     Open Access   (Followers: 3)
Journal of Spacecraft and Rockets     Full-text available via subscription   (Followers: 332)
Journal of Spatial Science     Hybrid Journal   (Followers: 1)
Journal of the American Helicopter Society     Full-text available via subscription   (Followers: 1)
Journal of the Astronautical Sciences     Hybrid Journal  
Microgravity Science and Technology     Hybrid Journal  
New Space     Hybrid Journal   (Followers: 2)
Nonlinear Dynamics     Hybrid Journal   (Followers: 5)
Population Space and Place     Hybrid Journal   (Followers: 2)
Proceedings of the Human Factors and Ergonomics Society Annual Meeting     Hybrid Journal  
Proceedings of the Institution of Mechanical Engineers Part G: Journal of Aerospace Engineering     Hybrid Journal   (Followers: 22)
Progress in Aerospace Sciences     Full-text available via subscription   (Followers: 46)
Propulsion and Power Research     Open Access   (Followers: 1)
Recent Patents on Space Technology     Full-text available via subscription  
Research & Reviews : Journal of Space Science & Technology     Full-text available via subscription  
Russian Aeronautics (Iz VUZ)     Hybrid Journal   (Followers: 14)
Space and Polity     Hybrid Journal   (Followers: 2)
Space Communications     Hybrid Journal   (Followers: 2)
Space Policy     Hybrid Journal   (Followers: 15)
Space Research Today     Full-text available via subscription   (Followers: 24)
Space Safety Magazine     Free   (Followers: 3)
Space Science Reviews     Hybrid Journal   (Followers: 10)
SpaceNews     Free   (Followers: 218)
Transportmetrica A : Transport Science     Hybrid Journal   (Followers: 1)
Вісник Національного Авіаційного Університету     Open Access   (Followers: 2)
Вестник УГАТУ     Open Access  
Journal Cover CEAS Aeronautical Journal
   Journal TOC RSS feeds Export to Zotero [23 followers]  Follow    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 1869-5582
     Published by Springer-Verlag Homepage  [2210 journals]
  • Analysis of trimmable conditions for a civil aircraft with active
           high-lift system
    • Abstract: Abstract This paper outlines recent flight dynamic analysis results of a civil aircraft with active high-lift system using blown Coandă flaps. The main focus lies in the trim analysis of the aircraft. Therefore, the basic structure and core elements of the nonlinear model, describing the dynamic behavior of an aircraft with this specific type of active high-lift system are presented. The center of gravity range allowing controllability and static stability of the aircraft is determined, and the resulting characteristics of the aerodynamic model and their impact on the trim results of the aircraft are analyzed. The results show specific flight dynamic difficulties related to the active high-lift system, namely in the flying characteristics necessary for safe take-off and approach procedures. The flight physics is explained and discussed. The necessity of the application of a wing leading edge device is outlined by preliminary studies and further remedial means are proposed.
      PubDate: 2014-09-11
       
  • A predictive envelope protection system using linear, parameter-varying
           models
    • Abstract: Abstract A parameter-varying, model-predictive envelope protection system is developed simplifying the controller structures required to keep the aircraft within a safe angle-of-attack and normal load factor envelope. The idea of a quasi-steady flight condition is used to map the flight envelope limits onto the setpoint values of a single flight control law. Since no mode switching is required, the selected level of automation, i.e., autopilot and flight management functionalities, is independent from the proximity to any angle-of-attack and normal load factor limit. In contrast to previous approaches, the proposed algorithm makes use of a quasi-linear, parameter-varying control loop model to adapt to the true nonlinear aircraft behavior. A variance-based sensitivity analysis highlights the most significant scheduling variables within this control loop model and, therefore, indicates the option of model reduction and improvement in efficiency, respectively. The proposed envelope protection system is evaluated throughout virtual flight tests with the unmanned flight test platform ULTRA-Dimona showing promising overall performance also in the presence of wind and turbulence.
      PubDate: 2014-09-06
       
  • Alternative fuels in aviation
    • Abstract: Abstract During the last years, the aviation sector has been looking into alternatives to kerosene from crude oil, to combat climate change by reduction of greenhouse gas (GHG) emissions and to ensure security of supply at affordable prices. The efforts are also a reaction to commitments and policy packages. Currently, a wide range of possible fuel candidates and fuel blends are discussed in the triple feedstock, process, and product. Any (synthetic) aviation fuel must be certified; hence, a profound knowledge on its properties, in particular thermophysical and chemical, is inevitable. In the present paper, an overview is given on alternative jet fuels, looking into the short-term and long-term perspective. Examples focusing on experimental and modeling work of combustion properties of existing—coal to liquid, gas to liquid (GtL)—and possible alternative fuels—GtL + 20 % 1-hexanol, GtL + 50 % naphthenic cut—are presented. Ignition delay times and laminar flame speeds were measured for different alternative aviation fuels over a range of temperatures, pressures, and fuel–air ratios. The data are used for the validation of a detailed chemical reaction mechanism following the concept of a surrogate. Such validated reaction models able to describe and to predict reliably important combustion properties of jet fuels are needed to further promote the development of even more sophisticated jet engines and to optimize synthetic jet fuel mixtures in practical combustors.
      PubDate: 2014-09-02
       
  • SFB 880: fundamentals of high lift for future commercial aircraft
    • Abstract: Abstract The recently founded Collaborative Research Centre SFB 880 of the Technische Universität Braunschweig, “Fundamentals of High-Lift for Future Commercial Aircraft”, develops new knowledge in aircraft noise, advanced approaches towards active high lift, and in the dynamics of flight with active high lift during short takeoff and landing operations. The research centre has therefore devised a range of research projects that aim at integrated aeroacoustic and aerodynamic design capabilities for drastic noise reductions and the generation of active high lift with an extremely high efficiency of the used onboard power. Flight dynamics of commercial aircraft with increased lift capabilities for takeoff and landing by means of active control and including the effects of aeroelasticity and engine failure modes are also investigated. The research centre has developed a joint strategy for technology assessment using high-quality conceptual design data of a reference aircraft that represents the state of the art in CO2 reductions, low noise, and short takeoff and landing for point-to-point air connections within Europe. The paper describes the overall strategy of the coordinated research work and gives examples of recent results.
      PubDate: 2014-09-01
       
  • Data parser approaches for (online) parameter estimation
    • Abstract: Abstract Finding maneuvers for parameter estimation in flight data records is a laborious task and traditionally performed post-flight on ground. Two different data parser approaches to automatically detect these maneuvers in flight are presented. Both methods search the control input signals for significant changes that correspond to test maneuvers. The first algorithm is based on the signal time derivative of the input signal whereas the second method uses a fast orthogonal wavelet transform. Both algorithms are tested with flight test data recorded with the DLR research aircraft ATTAS. Performance results are compared and potential problems when applying the parsers to other data are discussed. Results indicate that both methods are applicable in an online parameter estimation tool. The intention of the work in this paper is to develop an algorithm with a high level of automation for in-flight use, but both approaches could also be applied to offline flight data mining problems.
      PubDate: 2014-09-01
       
  • Aerodynamic performance of an over-the-wing propeller configuration at
           increasing Mach number
    • Abstract: Abstract Over-the-wing propeller configurations and particularly channel wing concepts show increased climb performance, and through effective acoustic shielding, reduced noise emissions when compared to a conventional tractor configuration. The main aerodynamic mechanisms could be identified by steady flow simulations of a simplified wing geometry and actuator disk. At take-off, where the thrust coefficient is very high, the drag of the wing decreases much stronger than the thrust of the propeller. This paper investigates the cruise conditions where the thrust coefficient is by one order of magnitude lower. The numerical results give evidence that, even at a moderate flight Mach number of 0.6, the beneficial influence of the over-the-wing propeller on the drag coefficient of the wing is negligibly small. On the other hand, the amount of propeller efficiency that is lost through high inflow velocity above the wing increases with Ma due to compressibility effects. As a result, the propulsive efficiency of an over-the-wing configuration is 16 % smaller than the reference (tractor). Semi-empirical correlations show that even at very low Mach numbers a drawback of at least 5 % remains. Although repositioning the propeller at the wing trailing edge may recover 4 % of the propulsive efficiency at Ma = 0.6, it is not advisable to give up most of the noise-shielding effect at take-off which is an important advantage of the channel wing.
      PubDate: 2014-09-01
       
  • Multidisciplinary analysis of CROR propulsion systems: DLR activities in
           the JTI SFWA project
    • Abstract: Abstract In the frame of the EU 7th Framework Joint Technology Initiative Smart Fixed Wing Aircraft project, the DLR Institute of Aerodynamics and Flow Technology (DLR-AS) is participating as an associated partner in the Airbus-led studies of the Contra-Rotating Open Rotor (CROR) as possible powerplant for future transport aircraft. Due to significant technical challenges in terms of noise emissions, installation effects and certification that still need to be addressed for this novel propulsion system, the numerical activities require the use of sophisticated multidisciplinary analysis tools and approaches covering aerodynamics, aeroacoustics and aeroelastics. In this paper an overview of the DLR-AS work in the project is given, which covers the numerical assessment of a novel noise reduction technology, an initial study of blade aeroelasticity as well as some in-depth studies on isolated and installed pusher-configuration CROR engine configurations. The first results of a validation of the numerical simulations using experimental test data that is being generated in Airbus-led low-speed wind tunnel tests are also presented.
      PubDate: 2014-09-01
       
  • Analysis of a multi-functional high-lift system driven by an active
           differential gear box
    • Abstract: Abstract A flight dynamics evaluation was performed to analyse the ability to use the outer flap for roll control as well. Based on the Airbus A350 flap system architecture, where the outer flap can be deployed independently from the inner flap using a so-called active differential gear box (ADGB), two different concepts were identified as potentially beneficial for the desired purpose. In both concepts, the inner ailerons were removed to save weight and system complexity and the outer flap performs (all speed) roll control together with the outer (low speed) aileron. Concept 1 comprises the usual flap geometry and the outer aileron, whereas concept 2 comprises an outer flap, which is extended in spanwise direction by the length of the inner aileron. Roll spoilers were not considered in the presented analyses. The flight dynamics evaluation revealed that a flap deflection rate of at least 16°/s is necessary to fulfil requirements from certification specification CS-25 and handling quality criteria. A system analysis showed that the existing ADGB is only able to deflect the flap with a maximum rate of 0.43°/s or 1.4°/s with slight modifications of the existing ADGB. These values showed to be insufficient for regular roll control. Nevertheless, in case of a dual loss of hydraulic power, the only available roll control could be performed by one remaining pair of ailerons, which are driven by an electrical back-up hydraulic actuator at the A350. In order to enable roll control, if these electrical back-up hydraulic actuators fail additionally, it was analysed whether the outer flap could be used as emergency roll control with the aforementioned feasible flap dynamics. The results showed that the handling qualities with this flap system ensuring roll control are barely controllable. However, it appears feasible to reach degraded but acceptable handling qualities if the system dynamics could be slightly increased.
      PubDate: 2014-09-01
       
  • Conceptual aircraft design with hybrid laminar flow control
    • Abstract: Abstract This paper describes a methodology for conceptual design and optimization of aircraft with hybrid laminar flow control (HLFC) systems integrated into wing and tails. An existing conceptual aircraft design platform is enhanced by the necessary methods for sizing of HLFC system architecture and prediction of aerodynamic drag polars. These include transonic drag characteristics as well as transition prediction by analysing boundary layer instability mechanisms. The implemented methods are described and its sensitivities against relevant aircraft design parameters are discussed. The integrated sizing methodology allows to assess the net benefit of HLFC system integration on overall aircraft level and to minimize aircraft fuel consumption by variation of aircraft design parameters, cruise conditions and HLFC system parameters. To demonstrate the applicability of the developed methodology in conceptual aircraft design it is used for design and assessment of an HLFC long-range passenger aircraft. The influence of the HLFC main drivers Mach number and wing sweep angle on aerodynamics, systems and aircraft design characteristics is investigated. Further, aircraft component resizing is analysed to further exploit the fuel reduction potential of the HLFC technology.
      PubDate: 2014-09-01
       
  • On the use of a steerable main landing gear for crosswind landing
           assistance
    • Abstract: Abstract Several crosswind-related incidents show that landing under heavy crosswind conditions can be challenging for pilots and may pose a threat to aviation or at least lead to higher pilot workload and/or irregularities in operations. For transport aircraft the common approach technique for crosswind landings is the so-called crabbed approach with wings level and a windward heading correction. This technique requires alignment of the aircraft with the runway prior to touchdown in order to keep lateral loads of the landing gear and tyres as low as possible and to maintain the controllability on ground after touchdown. The German Aerospace Center Institute of Flight Systems has used the idea of steerable main gears and developed a crosswind landing assistance system. During approach all gear struts are automatically aligned with the runway so that no decrab manoeuvre is required. On ground the assistance system uses each steerable landing gear, differential braking, and the aerodynamic control surfaces to control and stabilise the aircraft. After touchdown the aircraft is automatically aligned with the runway centreline and the still existing crab angle is slowly reduced. A simulator study with pilots in the loop using a model of a typical medium range transport aircraft was conducted in order to evaluate the benefits of such a landing technique. The study revealed that not only the aircraft controllability could be improved by landing in crabbed motion under strong crosswind conditions, but that the side forces acting on the landing gear can be reduced significantly as well. It was also shown that the use of steerable main landing gears is able to enlarge the spectrum of autoland operations, which is relatively limited at present in terms of maximum allowable crosswinds. All together the system has shown to be able to improve flight safety, lower the risk of weather-related delays due to go-arounds or diversions, and it also reduces structural loads on the landing gear during touchdown and landing.
      PubDate: 2014-09-01
       
  • Aerodynamic power and mechanical efficiency of bat airframes using a
           quasi-steady model
    • Abstract: Abstract Previous bat aerodynamic power models are refined by (1) varying the value of wing profile drag with lift coefficient, which varies with both flight speed and Reynolds number, (2) allowing for the aerodynamic cleanliness of head, body, ears and tail in calculating parasitic drag values at various speeds and according to airframe type, (3) incorporating models of wingbeat amplitude and frequency in the power calculations, and, (4) upgrading the allometric, phylogenetically corrected relationship between basal metabolic rate and body mass using data from 98 bat species. The fidelity of the aerodynamic power model is assessed using published wind tunnel data on a bat in steady glide. By comparing empirical published metabolic power (P met) values with values derived using the new aerodynamic model, we update estimates of in-flight musculoskeletal mechanical efficiency (η) for the airframes of eight bat species at steady level flight speeds. Furthermore, we calculate the increase in η at high speeds. The bats assessed range in body mass from 0.01 to 1 kg, and the comparison covers the speed range normally used by free-flying bats during their excursions. At their best endurance flight speeds (V end), η = 1.52 Ln (m bat) + 11.44 (%). At speeds > V end, η = η@ Vend + 1.3 (V−V end) (%). These equations yield accurate P met estimates for flight speeds within the range used for the steady level flight.
      PubDate: 2014-09-01
       
  • Comparing explicit and implicit modeling of rotor flapping dynamics for
           the EC 135
    • Abstract: Abstract To be valid up to higher frequencies, state space models derived by system identification methods have to include rotor states describing the dynamics of flapping and sometimes even downwash and regressive lag motion. In the case of flapping, the rigid body equations are usually augmented by the explicit differential equations for the longitudinal and lateral flapping angles which are then coupled to the rigid body equations through the corresponding force and moment terms. Alternatively, an implicit formulation can be used that includes the pitch and roll acceleration as model states. The paper compares the two modeling approaches for the EC 135 helicopter. For this helicopter, the formulation with flapping angles in its classical hybrid form shows some higher order deficiency in the match of the longitudinal and lateral accelerations, which are not apparent in the implicit model. After ruling out other effects, the discrepancies can be attributed to a vertical offset of the center of gravity from its assumed position. Once this offset is accounted for in the data, results from the two modeling approaches can be compared to each other and to theoretical predictions.
      PubDate: 2014-09-01
       
  • Aerodynamic and structural investigation of an active back-flow flap for
           dynamic stall control
    • Abstract: Abstract The design and experimental investigation of a back-flow flap for helicopter dynamic stall control is described. A spoiler-type flap is designed, and shown by CFD to reduce the pitching moment peak during dynamic stall by 34 %. Initial experiments with a passively actuated flap in a low-speed wind tunnel showed that the opening and closing times for the flap due to the aerodynamic forces are sufficiently short and that the flap is not affected by the inertial forces of the model pitching. The experiments showed the need for a flap restraint, and that an active actuation is needed so that the flap angle is sufficient at the time of stall to have a control effect. Initial demonstrators for the structural concept of the active back-flow flap using glass fiber reinforced polymer and a solid state hinge are presented, showing the possibility of fabrication as an after-market add-on.
      PubDate: 2014-09-01
       
  • Parametric design studies for propulsive fuselage aircraft concepts
    • Abstract: Abstract Breaking with the classical separation of airframe and power plant system, new synergy effects may be rooted in close design coupling and the approach of distributing the production of thrust along the main components of the airframe. Beside greater configurational flexibility, airframe structural relief, improved noise shielding, and, the potential for control power augmentation, distributed propulsion is particularly interesting due to the reduced propulsive power demands expected from the notion of aircraft wake filling. In previous work, the concept of a propulsor encircling the aft fuselage with intent to entrain the fuselage boundary layer was identified to be one of the most promising concepts for aircraft wake filling. In this paper, the analytical basis for the quantification of efficiency benefits connected to the propulsive fuselage concept is discussed. Appropriate control volume and consistent efficiency chain definitions are introduced. A simplified boundary layer model is derived from axisymmetric fuselage CFD simulation and used to determine the momentum deficit ingested by the fuselage propulsor. Based on a novel figure of merit for vehicular efficiency, the energy-specific air range, ESAR, the dependency of aircraft cruise efficiency on basic propulsion system and aircraft design changes is parametrically investigated. Specifically, the sensitivities of vehicular efficiency w.r.t. wing aspect ratio and flow transition characteristics, propulsor size, and aircraft design cruise Mach number are studied.
      PubDate: 2014-08-22
       
  • Hans-Peter Kreplin, retired
    • PubDate: 2014-08-13
       
  • Design considerations for the components of electrically powered active
           high-lift systems in civil aircraft
    • Abstract: Abstract To address the challenges of future air traffic, such as more accessible air travel with better public acceptance, this research work focuses on efficient active high-lift systems (AHLS). This system applies boundary layer suction combined with a controlled Coanda jet. Electrically powered compressors are located in the wings at each flap to supply the suction and blowing air mass flow rate to the AHLS, thus coupling the two in a useful way. This concept provides flexibility and controllability of lift generation and is consistent with the trend towards an “all-electric aircraft”. General models for assessment of such systems in preliminary aircraft design are not available yet as they require interdisciplinary expertise. This paper provides general design considerations for the components of this type of electrically powered AHLS, comprising compressors, motors, power electronics, system peripherals, and generators. The conceptual design for those components results in models for preliminary aircraft design which allows estimating power consumption, size and mass.
      PubDate: 2014-08-09
       
  • Influence of an imidazolium salt on the curing behaviour of an epoxy-based
           hot-melt prepreg system for non-structural aircraft applications
    • Abstract: Abstract This study investigates the influence of an imidazolium salt as initiator for the curing of an epoxy novolac-based hot-melt prepreg resin system for production of non-structural aircraft components. The salt decomposes at a specific temperature during curing, yielding an imidazole. This molecule initiates a fast anionic homopolymerization. The effect of the imidazolium salt on the curing kinetics is studied extensively by differential scanning calorimetry (DSC) as a function of its concentration. Onset and peak temperatures of the curing reactions are determined from dynamic DSC experiments at various heating rates. The curing behaviour at 140 °C is analysed in more detail by isothermal DSC measurements. Calculated isothermal conversion curves prove that the flame retarded epoxy novolac formulation can be cured within less than 60 min at this specific temperature by introducing six parts of the imidzolium salt per hundred parts of preformulated resin. At the same time glass transition temperatures above 130 °C evaluated by DSC or app. 155 °C determined by DMA can be reached.
      PubDate: 2014-08-07
       
  • Numerical investigation of the influence of the camber distribution at the
           rotor tip on the efficiency at different tip clearances
    • Abstract: Abstract The present paper reports on numerical investigations into the relationship of compressor efficiency drop due to increased rotor tip clearance and the rotor tip camber distribution in a 1.5 stage low-speed axial flow compressor. Starting from a baseline compressor, six alternative designs were derived. In these redesigns the tip section camber line of the rotor was replaced by an analytically given camber distribution. These camber lines used for the redesigns ranged from extreme front load to extreme rear load. The new camber line styles were blended into the original blade over the upper 30 % of blade height. For each of these variations a design speed characteristic was calculated for five different rotor tip clearances. From these characteristics the compressor efficiency at the design flow rate was extracted. Based on these values an exchange rate could be calculated relating compressor overall efficiency to rotor tip clearance height. It turned out that the rotor tip camber line style does not have an impact on this exchange rate. It could be shown that rotor losses are only affected slightly by the rotor tip camber line style and that the pressure rise that the tip vortex experiences as it travels through the passage is generally unchanged from one tip camber line style to the other.
      PubDate: 2014-08-07
       
  • Flight control law design criteria for the transition phase for a tiltwing
           aircraft using multi-objective parameter synthesis
    • Abstract: Abstract Aircraft in tiltwing configuration combine the advantages of helicopters, such as hovering and vertical take-off and landing capabilities (VTOL), with the advantages of conventional fixed-wing aircraft, in particular long endurance and economic flight at higher velocities. During the transition phase between hovering and aerodynamic horizontal forward flight the aerodynamic forces and moments, the direct forces due to propulsion system and propulsion-induced aerodynamic forces and moments have to be properly balanced. Tilting the wing from vertical to horizontal position (and vice versa) poses a significant change in configuration. In combination with the given large velocity range this influences the control device efficiency significantly. At the same time, the tilting of the wing provides an additional control parameter. During flight control law design for an unmanned tiltwing aircraft with focus on the transition phase multi-objective parameter analysis and synthesis provides a powerful means to identify interdependencies and sensitivities. Key aspects of the longitudinal motion during the transition phase are investigated in this study using the multi-objective parameter synthesis tool MOPS, developed by the DLR Institute of System Dynamics and Control. Aim of this paper is to analyze quality criteria with respect to design and evaluation of control laws during transition phase. To achieve these parameters forward velocity and pitch attitude controller are optimized with respect to control and disturbance responses. At the same time the overall robustness against selected uncertain model parameters, such as actuator dynamics is considered explicitly. Different quality criteria characterizing these motions are developed and discussed in detail.
      PubDate: 2014-08-05
       
  • Speeding-up the computation of high-lift aerodynamics using a
           residual-based reduced-order model
    • Abstract: Abstract In this article, we propose a strategy for speeding-up the computation of the aerodynamics of industrial high-lift configurations using a residual-based reduced-order model (ROM). The ROM is based on the proper orthogonal decomposition (POD) of a set of solutions to the Navier–Stokes equations governing fluid flow at different parameter values, from which a set of orthogonal basis vectors is evaluated. By considering an initial set of few snapshots at different angles of attack, a ROM is constructed which is used to predict a solution at an angle of attack which is just outside the space spanned by the POD basis vectors. The ROM solution is subsequently used to initialize the flow solver for an accurate calculation of the aerodynamics at the same flow condition. This procedure is conducted repetitively for a series of angles of attack, whereby for each and every ROM prediction, the snapshots set is augmented with the latest CFD computed flow solution. Using this strategy, a considerable reduction in the total number of iterations to reach the converged steady-state solution is achieved when compared with conventional computational techniques used in industry for a series of computations such as drag polar computations. The methodology is applied and demonstrated on a two-element airfoil and a body-wing aircraft in high-lift configuration. Furthermore, an investigation is conducted on the behavior of the reduced-order modeling approach at angles of attack close to and within the static stall region, where aerodynamic hysteresis may occur and the aerodynamic coefficients are found to be multiple-valued functions of the angle of attack. It is revealed that by constructing the ROM from an appropriate set of basis vectors, it is also possible to model the resulting bifurcation.
      PubDate: 2014-08-03
       
 
 
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