The Experts below are selected from a list of 231 Experts worldwide ranked by ideXlab platform

Markus Raffel - One of the best experts on this subject based on the ideXlab platform.

  • Boundary Layer Transition Measured by DIT on the PSP Rotor in Forward Flight
    Journal of the American Helicopter Society, 2021
    Co-Authors: Anthony Donald Gardner, C. Christian Wolf, A. Weiss, James T. Heineck, A.d. Overmeyer, H.r. Spooner, R.k. Jain, Markus Raffel
    Abstract:

    A well-defined reference set of data for computational fluid dynamics and comprehensive code validation for a scaled helicopter main rotor with Boundary Layer Transition in forward flight is presented. The Boundary Layer Transition was measured using differential infrared thermography (DIT) on the top (suction) side of the NASA/Army “PSP rotor” in the NASA Langley 14-by-22-Foot Subsonic Tunnel. The tests used a FLIR X8500 SLS long-wave infrared camera to observe the three-bladed rotor. The Boundary Layer Transition was detected for forward flight at an advance ratio of 0.3 (115 kt). The measured Boundary Layer Transition positions are consistent with previous measurements and predicted Boundary Layer Transition locations. A method for the analysis of DIT images for a rotor in forward flight is shown and validated based on computational analysis of a pitching airfoil with varying inflow, showing both qualitative and quantitative similarity to experimental data.

  • Helicopter Rotor Boundary Layer Transition Measurement in Forward Flight Using an Infrared Camera
    Journal of the American Helicopter Society, 2020
    Co-Authors: Anthony Donald Gardner, C. Christian Wolf, James T. Heineck, Miles Barnett, Markus Raffel
    Abstract:

    Boundary Layer Transition measurement was demonstrated using differential infrared thermography on the top side of a helicopter rotor in forward flight. The tests used a FLIR X8500xc SLS long wave infrared camera to observe the DLR EC135 test helicopter rotor. The Boundary Layer Transition was detected for hover out of ground effect (150 ft) and for forward flight at 80 kt (1700 ft). The measured Boundary Layer Transition positions are consistent with previous measurements of the EC135 hovering in ground effect, and with predicted Boundary Layer Transition positions. A method for the analysis of DIT images for a rotor in forward flight is shown, based on computational analysis of a pitching airfoil with varying inflow.

  • On the Effect of Rotational Forces on Rotor Blade Boundary-Layer Transition
    AIAA Journal, 2019
    Co-Authors: Armin Weiss, Anthony Donald Gardner, Christian Klein, Till Schwermer, Markus Raffel
    Abstract:

    Laminar-turbulent Boundary-Layer Transition is investigated on the suction side of Mach-scaled helicopter rotor blades in climb and analyzed in view of the effect of rotational forces. Transition p...

  • Analysis of differential infrared thermography for Boundary Layer Transition detection
    Experiments in Fluids, 2017
    Co-Authors: Anthony Donald Gardner, C. Christian Wolf, C. Eder, Markus Raffel
    Abstract:

    This paper presents an analysis of the differential infrared thermography (DIT) technique, a contactless method of measuring the unsteady movement of the Boundary Layer Transition position on an unprepared surface. DIT has been shown to measure Boundary Layer Transition positions which correlate well with those from other measurement methods. In this paper unsteady aerodynamics from a 2D URANS solution are used and the resulting wall temperatures computed. It is shown that the peak of the temperature difference signal correlates well with the Boundary Layer Transition position, but that the start and end of Boundary Layer Transition cannot be extracted. A small systematic time-lag cannot be reduced by using different surface materials, but the signal strength can be improved by reducing the heat capacity and heat transfer of the surface Layer, for example by using a thin plastic coating. Reducing the image time separation used to produce the difference images reduces the time-lag and also the signal level, thus the optimum is when the signal to noise ratio is at the minimum which can be evaluated.

  • differential infrared thermography for Boundary Layer Transition detection on pitching rotor blade models
    Experiments in Fluids, 2015
    Co-Authors: Markus Raffel, Christoph B Merz, Till Schwermer, Kai Richter
    Abstract:

    Differential infrared thermography (DIT) was investigated and applied for the detection of unsteady Boundary Layer Transition locations on a pitching airfoil and on a rotating blade under cyclic pitch. DIT is based on image intensity differences between two successively recorded infrared images. The images were recorded with a high framing rate infrared camera. A pitching NACA0012 airfoil served as the first test object. The recorded images were used in order to investigate and to further improve evaluation strategies for periodically moving Boundary Layer Transition lines. The measurement results are compared with the results of unsteady CFD simulations based on the DLR-TAU code. DIT was then used for the first time for the optical measurement of unsteady Transition locations on helicopter rotor blade models under cyclic pitch and rotation. Image de-rotation for tracking the blade was employed using a rotating mirror to increase exposure time without causing motion blur. The paper describes the challenges that occurred during the recording and evaluation of the data in detail. However, the results were found to be encouraging to further improve the method toward the measurement of unsteady Boundary Layer Transition lines on helicopter rotor models in forward flight.

Anthony Donald Gardner - One of the best experts on this subject based on the ideXlab platform.

  • Boundary Layer Transition Measured by DIT on the PSP Rotor in Forward Flight
    Journal of the American Helicopter Society, 2021
    Co-Authors: Anthony Donald Gardner, C. Christian Wolf, A. Weiss, James T. Heineck, A.d. Overmeyer, H.r. Spooner, R.k. Jain, Markus Raffel
    Abstract:

    A well-defined reference set of data for computational fluid dynamics and comprehensive code validation for a scaled helicopter main rotor with Boundary Layer Transition in forward flight is presented. The Boundary Layer Transition was measured using differential infrared thermography (DIT) on the top (suction) side of the NASA/Army “PSP rotor” in the NASA Langley 14-by-22-Foot Subsonic Tunnel. The tests used a FLIR X8500 SLS long-wave infrared camera to observe the three-bladed rotor. The Boundary Layer Transition was detected for forward flight at an advance ratio of 0.3 (115 kt). The measured Boundary Layer Transition positions are consistent with previous measurements and predicted Boundary Layer Transition locations. A method for the analysis of DIT images for a rotor in forward flight is shown and validated based on computational analysis of a pitching airfoil with varying inflow, showing both qualitative and quantitative similarity to experimental data.

  • Helicopter Rotor Boundary Layer Transition Measurement in Forward Flight Using an Infrared Camera
    Journal of the American Helicopter Society, 2020
    Co-Authors: Anthony Donald Gardner, C. Christian Wolf, James T. Heineck, Miles Barnett, Markus Raffel
    Abstract:

    Boundary Layer Transition measurement was demonstrated using differential infrared thermography on the top side of a helicopter rotor in forward flight. The tests used a FLIR X8500xc SLS long wave infrared camera to observe the DLR EC135 test helicopter rotor. The Boundary Layer Transition was detected for hover out of ground effect (150 ft) and for forward flight at 80 kt (1700 ft). The measured Boundary Layer Transition positions are consistent with previous measurements of the EC135 hovering in ground effect, and with predicted Boundary Layer Transition positions. A method for the analysis of DIT images for a rotor in forward flight is shown, based on computational analysis of a pitching airfoil with varying inflow.

  • Advanced infrared thermography data analysis for unsteady Boundary Layer Transition detection
    Measurement Science and Technology, 2019
    Co-Authors: Christoph Mertens, C. Christian Wolf, Anthony Donald Gardner, F.f.j. Schrijer, B. W. Van Oudheusden
    Abstract:

    Advanced data processing methods for detecting unsteady Boundary Layer Transition in periodic aerodynamic processes by means of infrared thermography measurements are presented. The thermal radiation emitted from the heated suction surface of a pitching airfoil model in subsonic flow is measured with an infrared camera. The unsteady Boundary Layer Transition location is detected by analyzing the difference in the infrared radiation signal over short periods of time with differential infrared thermography (DIT). The DIT method is optimized and automated in the present study, which facilitates the extension of the part of the motion period where valid DIT Transition measurements are produced. Additionally, a new infrared thermography data processing method is introduced in this study. The extraction of the extrema of the measured radiation signal at fixed locations on the model surface yields instants of the motion period that relate to the occurrence of Boundary Layer Transition. The local infrared thermography (LIT) approach can be extended to measuring the two-dimensional unsteady Boundary Layer Transition front.

  • Unsteady Boundary Layer Transition Detection with Local Infrared Thermography
    Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 2019
    Co-Authors: Christoph Mertens, C. Christian Wolf, Anthony Donald Gardner
    Abstract:

    A new approach to measuring unsteady Boundary Layer Transition in periodic processes with infrared thermography is introduced. The radiation from the heated suction surface of a pitching airfoil model is measured with an infrared camera. The extraction of the extrema of the measured radiation signal at fixed model locations yields instants of the motion phase that correlate with the occurrence of Boundary Layer Transition. The analysis of the extrema of the signal’s gradient produces results that are equivalent to the results acquired by optimized differential infrared thermography, and it provides insight into the origins of the systematic error of that technique. It is demonstrated that the local infrared thermography approach can be readily extended to measuring two-dimensional Boundary Layer Transition fronts.

  • On the Effect of Rotational Forces on Rotor Blade Boundary-Layer Transition
    AIAA Journal, 2019
    Co-Authors: Armin Weiss, Anthony Donald Gardner, Christian Klein, Till Schwermer, Markus Raffel
    Abstract:

    Laminar-turbulent Boundary-Layer Transition is investigated on the suction side of Mach-scaled helicopter rotor blades in climb and analyzed in view of the effect of rotational forces. Transition p...

Scott A. Berry - One of the best experts on this subject based on the ideXlab platform.

  • Secondary Side Considerations for Boundary Layer Transition Flight Experiment
    Journal of Spacecraft and Rockets, 2021
    Co-Authors: Scott A. Berry, Bradley M. Wheaton, Brandon C. Chynoweth
    Abstract:

    The Boundary Layer Transition (BOLT) Flight Experiment is to launch soon on a sounding rocket to obtain hypersonic data on a complex geometry with swept leading edges and concave surfaces. BOLT was...

  • Aerothermodynamic Ground Tests in Support of the Boundary Layer Transition Flight Experiment
    Journal of Spacecraft and Rockets, 2021
    Co-Authors: Elizabeth Rieken, Scott A. Berry, Michelle L. Mason, Francis A. Greene
    Abstract:

    The U.S. Air Force Research Laboratory/U.S. Air Force Office of Scientific Research has sponsored the Boundary Layer Transition (BOLT) experiment to investigate hypersonic Boundary-Layer Transition...

  • Flight Experiment Verification of Shuttle Boundary Layer Transition Prediction Tool
    46th AIAA Thermophysics Conference, 2016
    Co-Authors: Scott A. Berry, Karen T. Berger, Thomas J. Horvath, William A. Wood
    Abstract:

    Boundary Layer Transition at hypersonic conditions is critical to the design of future high-speed aircraft and spacecraft. Accurate methods to predict Transition would directly impact the aerothermodynamic environments used to size a hypersonic vehicle's thermal protection system. A Transition prediction tool, based on wind tunnel derived discrete roughness correlations, was developed and implemented for the Space Shuttle return-to-flight program. This tool was also used to design a Boundary Layer Transition flight experiment in order to assess correlation uncertainties, particularly with regard to high Mach-number Transition and tunnel-to-flight scaling. A review is provided of the results obtained from the flight experiment in order to evaluate the Transition prediction tool implemented for the Shuttle program.

  • Orbiter Boundary Layer Transition Prediction Tool Enhancements
    48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, 2010
    Co-Authors: Scott A. Berry, Rudolph A. King, Michael A. Kegerise, William A. Wood, Catherine B. Mcginley, Karen T. Berger, Brian Anderson
    Abstract:

    Updates to an analytic tool developed for Shuttle support to predict the onset of Boundary Layer Transition resulting from thermal protection system damage or repair are presented. The Boundary Layer Transition tool is part of a suite of tools that analyze the local aerothermodynamic environment to enable informed disposition of damage for making recommendations to fly as is or to repair. Using mission specific trajectory information and details of each d agmea site or repair, the expected time (and thus Mach number) of Transition onset is predicted to help define proper environments for use in subsequent thermal and stress analysis of the thermal protection system and structure. The Boundary Layer Transition criteria utilized within the tool were updated based on new local Boundary Layer properties obtained from high fidelity computational solutions. Also, new ground-based measurements were obtained to allow for a wider parametric variation with both protuberances and cavities and then the resulting correlations were calibrated against updated flight data. The end result is to provide correlations that allow increased confidence with the resulting Transition predictions. Recently, a new approach was adopted to remove conservatism in terms of sustained turbulence along the wing leading edge. Finally, some of the newer flight data are also discussed in terms of how these results reflect back on the updated correlations.

  • Roles of Engineering Correlations in Hypersonic Entry Boundary Layer Transition Prediction
    48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, 2010
    Co-Authors: Charles H. Campbell, Scott A. Berry, Rudolph A. King, Michael A. Kegerise, Thomas J. Horvath
    Abstract:

    Efforts to design and operate hypersonic entry vehicles are constrained by many considerations that involve all aspects of an entry vehicle system. One of the more significant physical phenomenon that affect entry trajectory and thermal protection system design is the occurrence of Boundary Layer Transition from a laminar to turbulent state. During the Space Shuttle Return To Flight activity following the loss of Columbia and her crew of seven, NASA's entry aerothermodynamics community implemented an engineering correlation based framework for the prediction of Boundary Layer Transition on the Orbiter. The methodology for this implementation relies upon similar correlation techniques that have been is use for several decades. What makes the Orbiter Boundary Layer Transition correlation implementation unique is that a statistically significant data set was acquired in multiple ground test facilities, flight data exists to assist in establishing a better correlation and the framework was founded upon state of the art chemical nonequilibrium Navier Stokes flow field simulations. Recent entry flight testing performed with the Orbiter Discovery now provides a means to validate this engineering correlation approach to higher confidence. These results only serve to reinforce the essential role that engineering correlations currently exercise in the design and operation of entry vehicles. The framework of information related to the Orbiter empirical Boundary Layer Transition prediction capability will be utilized to establish a fresh perspective on this role, and to discuss the characteristics which are desirable in a next generation advancement. The details of the paper will review the experimental facilities and techniques that were utilized to perform the implementation of the Orbiter RTF BLT Vsn 2 prediction capability. Statistically significant results for multiple engineering correlations from a ground testing campaign will be reviewed in order to describe why only certain correlations were selected for complete implementation to support the Shuttle Program. Historical Orbiter flight data on early Boundary Layer Transition due to protruding gap fillers will be described in relation to the selected empirical correlations. In addition, Orbiter entry flight testing results from the BLT Flight Experiment will be discussed in relation to these correlations. Applicability of such correlations to the entry design problem will be reviewed, and finally a perspective on the desirable characteristics for a next generation capability based on high fidelity physical models will be provided.

Christian Klein - One of the best experts on this subject based on the ideXlab platform.

  • On the Effect of Rotational Forces on Rotor Blade Boundary-Layer Transition
    AIAA Journal, 2019
    Co-Authors: Armin Weiss, Anthony Donald Gardner, Christian Klein, Till Schwermer, Markus Raffel
    Abstract:

    Laminar-turbulent Boundary-Layer Transition is investigated on the suction side of Mach-scaled helicopter rotor blades in climb and analyzed in view of the effect of rotational forces. Transition p...

  • Influence of suction on step-induced Boundary-Layer Transition
    2018
    Co-Authors: Benjamin Dimond, Marco Costantini, Steffen Risius, Carsten Fuchs, Christian Klein
    Abstract:

    The influence of suction on step-induced Boundary-Layer Transition has been experimentally investigated in the Cryogenic Ludwieg-Tube Goettingen at large chord Reynolds numbers (up to 16 MIllion), Mach numbers from 0.35 to 0.77 and various stream wise pressure gradients by means of Temperature-Sensitive Paint (TSP). Surface imperfections, implemented as combination of gap and forward facing step, caused Transition to occur at a location more upstream than in case of a smooth surface (i.e. without gap and step). It was found that suction, achieved passively by exploiting the pressure difference between upper and lower side of the model, induced a movement of Transition to a more downstream location than on the smooth configuration at the same test conditions. Thus, the effect of suction was to even overcompensate the adverse effect of the combination of gap and forward-facing step on Boundary-Layer Transition.

  • Boundary-Layer Transition measurements on Mach-scaledhelicopter rotor blades in the rotating testfacility Göttingen
    2017
    Co-Authors: Armin Weiss, Anthony Donald Gardner, Christian Klein
    Abstract:

    : Boundary-Layer Transition plays an important role in rotating blade aerodynamics affecting the performance of modern helicopter rotor blades such as low Reynolds number model rotors. However, advanced computational fluid dynamics (CFD) codes used for performance prediction purposes including modeling of this phenomenon on rotating blades are still in development and lack experimental data for validation purposes. This work presents spatially high resolved experimental Boundary-Layer Transition data on the suction side of model helicopter blades in climb at relative radial positions between 0.4

  • Pressure Gradient and Nonadiabatic Surface Effects on Boundary Layer Transition
    AIAA Journal, 2016
    Co-Authors: Marco Costantini, Stefan Hein, Ulrich Henne, Christian Klein, Stefan Koch, Lukas Schojda, Vladimir Ondrus, Wolfgang Schröder
    Abstract:

    The influence of the streamwise pressure gradient and a nonadiabatic surface on Boundary Layer Transition was experimentally investigated at the Cryogenic Ludwieg-Tube Gottingen, Germany. Boundary Layer Transition was detected nonintrusively by means of the temperature-sensitive paint technique. The wind-tunnel model was designed to achieve a quasi-uniform streamwise pressure gradient over a large portion of the model chord length. This allowed the effects on Boundary Layer Transition of the streamwise pressure gradient and wall temperature ratio to be decoupled. The model was tested at high Reynolds numbers and at a high subsonic Mach number. Favorable, almost-zero, and adverse streamwise pressure gradients were considered; and various temperature differences between the flow and the model surface were implemented. Stronger flow acceleration and lower wall temperature ratios led to an increase of the Transition Reynolds number. Larger increases in the Transition Reynolds number were obtained at more pron...

Raffel Markus - One of the best experts on this subject based on the ideXlab platform.

  • Unsteady Boundary-Layer Transition Measurements and Computations on a Rotating Blade under Cyclic Pitch Conditions
    'Springer Science and Business Media LLC', 2020
    Co-Authors: Weiss Armin, Braukmann, Johannes N., Kaufmann Kurt, Wolf C. Christian, Heineck, James T., Raffel Markus
    Abstract:

    The presented work tackles the lack of experimental investigations of unsteady laminar-turbulent Boundary-Layer Transition on rotor blades at cyclic pitch actuation, which are important for accurate performance predictions of helicopters in forward flight. Unsteady Transition positions were measured on the blade suction side of a four-bladed subscale rotor by means of non-intrusive differential infrared thermography (DIT). Experiments were conducted at different rotation rates corresponding to Mach and Reynolds numbers at 75% rotor radius of up to M_75=0.21 and Re_75 =3.3×10^5 and with varying cyclic blade pitch settings. The setup allowed Transition to be measured across the outer 54% of the rotor radius. For comparison, Transition was also measured using conventional infrared thermography for steady cases with collective pitch settings only. The study is complemented by numerical simulations including Boundary-Layer Transition modeling based on semi-empirical criteria. DIT results reveal the upstream and downstream motion of Boundary-Layer Transition during upstroke and downstroke, a reasonable comparison to experimental results obtained using the already established sigma*c_p method, and noticeable agreement with numerical simulations. The result is the first systematic study of unsteady Boundary-Layer Transition on a rotor suction side by means of DIT including a comparison to numerical computations

  • Helicopter Rotor Boundary Layer Transition Measurement in Forward Flight Using an Infrared Camera
    'American Helicopter Society', 2020
    Co-Authors: Gardner, Anthony D., Wolf C. Christian, Heineck, James T., Barnett Miles, Raffel Markus
    Abstract:

    Boundary Layer Transition measurement was demonstrated using differential infrared thermography (DIT) on the top side of a helicopter rotor in forward flight, which detects the difference in the convective heat transfer at the Boundary Layer Transition position. The tests used a FLIR X8500xc SLS long wave infrared camera to observe the DLR EC135 test helicopter rotor. The Boundary Layer Transition was detected for hover out of ground effect (150 ft) and for forward flight at 80 kt (1700 ft). The measured Boundary Layer Transition positions are consistent with previous measurements of the EC135 hovering in ground effect, and with predicted Boundary Layer Transition positions. A method for the analysis of DIT images for a rotor in forward flight is shown, based on computational analysis of a pitching airfoil with varying inflow