- Particle Image Velocimetry Development of a Promising Tool for In-Flight Flow Field Measurements

Transcription

1 - Particle Image Velocimetry Development of a Promising Tool for In-Flight Flow Field Measurements C. Politz, R. Konrath, A. Schröder, J. Agocs German Aerospace Center (DLR Göttingen) Institute of Aerodynamics and Flow Technology A. Grüttemann, M. Kreienfeld German Aerospace Center (DLR Braunschweig) Institute of Flight Guidance N. Lawson Cranfield University christina.politz@dlr.de Internet:

2 Motivation Measurement campaign was part of the European research project AIM (Advanced In-Flight Measurement Techniques) within the 6th Framework Programme of the European Community Development of advanced non-intrusive in-flight measurement techniques for in-flight testing and research on real aircraft and helicopters Measurements of pressure distributions, thermal loads, wing and propeller deformation and velocity fields 11 participating European organisations 2

3 Objectives Application and assessment of Particle Image Velocimetry (PIV) for inflight flow measurements TRL 4 TRL 7 + Experimental Approach Determination of a feasible PIV system and its installation inside a research aircraft Certification of the predefined setup Non-intrusive measurements under free flight conditions with changing aircraft settings (e.g. flaps, velocity, etc.) Evaluation of measurement data including the effects of in-flight environment on measurement method (e.g. choice of seeding, system integration) + Reference: 3

4 Outline Experimental Methodology Experimental Setup Flight Tests & Results Conclusion & Outlook 4

5 Experimental Methodology: Particle Image Velocimetry 5

6 Experimental Methodology: Particle Image Velocimetry Sample Raw Image 1st Frame 2nd Frame 6

7 Outline Experimental Methodology Experimental Setup Flight Tests & Results Conclusion & Outlook 7

8 Experimental Setup: Test Bed FD Spherical Window Camera Window Laser Light Sheet Aircraft Type: Dornier Do Call Sign: Span: Height: D-CODE m 4.86 m Wing Area: 32 m² Laser Light Exit Empty Weight: Max. TOW: appr kg kg Engine: 2 x Garret TPE Power: V MO : each 715 SHP 200 KIAS (< ft) Source: adjusted by Fritz Boden Max. Altitude: ft (7 600 m) 8

9 Experimental Setup: Installations Inside the Aircraft Cabin 9

10 Experimental Setup: Tracer Particles Flight tests took place between 900 3,000 m altitude Occurring cloud types: Cumulus, Nimbostratus, Stratus, Stratocumulus with mean droplet diameters between 4-80 µm 1 Likeliness of velocity lag not determinable yet due to unavailable reference measurement Raw image of the first camera frame (single exposed): 1: Houghton H.G.: On the Physics of Clouds and Precipitation, ed. By Malone T.F., Compendium of Meteorology, American Meteorological Society, Waverly Press Inc., Baltimore / USA, pp ,

11 Experimental Setup: PIV Recording Parameter Flow structure characteristics: Field of view: Observation distance: Recording method: Recording medium: Recording lens: Illumination: Pulse delay: Seeding material: aircraft velocity: m/s (Re ~ ), outer fuselage boundary layer, propeller slipstream, flap downwash 68 x 90 mm² ~ 120 mm 1 st & 2 nd flight test: single frame/double exposure 3 rd flight test: double frame/single exposure digital 14 bit CCD camera system 1600 x 1200 pixel f = 21 mm Nd: YAG Laser nm (double pulse) t =10µs natural aerosols / cloud droplets 11

12 Experimental Setup: Certification & Laser Safety In-flight PIV modification of research aircraft Do Flight test installation has to be qualified according to FAR 23 All equipment temporally installed inside the aircraft cabin Little influence on weight and balance Main tasks for certification Proof of structure concerning emergency or gust loads Electrical supply and safety Cabin layout in accordance with emergency procedures Laser safety (operation of class 4 laser system) 3 criteria have to be covered: Looking directly into the beam Diffuse reflections Observers on the ground with optical instruments e.g. binocular Laser operation only in cruise between 900 and 3000 m 12

13 Outline Experimental Methodology Experimental Setup Flight Tests & Results Conclusion & Outlook 13

14 1st & 2nd Flight Test: Results (Autocorrelation) Very first flight test: o vias ~ 96 m/s o flaps retracted o altitude ~ 1500 m Cloud layer: Stratocumulus Autocorrelation sequence employed (due to over-exposure of second camera frame) Sequence of 27 images with t=0.1s (first camera frame, double exposed ) 14

15 3 rd Flight Test: Results (Cross Correlation) v IAS = 75 m/s, Altitude = 1500 m, Flaps retracted 15

16 3rd Flight Test: Results (Cross Correlation) 16

17 Outline Experimental Methodology Experimental Setup Flight Tests & Results Conclusion & Outlook 17

18 Conclusion Flight tests showed feasibility PIV for in-flight applications Certification process of installed PIV setup lasted more than 4 months Restrictions have been defined for safe laser operation during flight Using cloud particles as seeding leads to viable PIV results Problems occurred with camera overexposure during daylight measurements ad hoc solution: Flight close to dusk Applying autocorrelation technique 18

19 Outlook Further adjustments of the PIV system will enhance performance Improved laser safety installation to allow night flights Alternative: application of (mechanical) shutter for daylight tests Further analysis of natural particles or investigation of possibilities for artificially introduced seeding Different orientation and positions of laser light sheet to investigate distinct critical parts of the flow around the aircraft Observation of larger measurement areas Further flight tests with larger aircraft (e.g. A320 D-ATRA ) are already under consideration and scheduled in future projects (AIM², DLR projects) 19