 | Klinner J. Development and assessment of volume resolving velocimetry for turbomachinery test facilities: Diss. … Dr.-Ing. / Deutsches Zentrum für Luft- und Raumfahrt, Institut für Antriebstechnik, Köln. - Köln: DLR, 2017. - x, 194 p.: ill., tab. - (Forschungsbericht; 2017-52). - Res. also Germ. - Bibliogr.: p.171-190. - ISSN 1434-8454
Шифр:(Pr 1120/2017-52) 02
|
Nomenclature ................................................... iv
1 Introduction ................................................. 1
1.1 Motives for volume resolving velocimetry in
turbomachinery test facilities .......................... 1
1.2 Techniques for tracer-based three component
velocimetry in a volume ................................. 4
1.3 Optical spray diagnostics - from pointwise to
volumetric measurements ................................. 8
1.4 Objectives of the thesis ............................... 11
1.4.1 Implementation of Tomographic PIV in
a transonic cascade wind tunnel ................. 11
1.4.2 Implementation of tomographic shadowgraphy for
fuel sprays at elevated pressure and
temperature ..................................... 11
1.5 Outline ................................................ 12
2 Fundamentals of tomographic particle image velocimetry and
state of the art ............................................ 13
2.1 Operating principle of tomographic PIV ................. 13
2.2 Camera calibration ..................................... 14
2.3 Aspects of volume imaging of small particles ........... 17
2.3.1 Particle image size ............................. 17
2.3.2 Depth of focus .................................. 19
2.3.3 Viewing geometry and particle elongation ........ 21
2.3.4 Scattering behaviour ............................ 22
2.3.5 Seeding density ................................. 23
2.4 Particle field reconstruction .......................... 24
2.4.1 The ambiguity problem ........................... 24
2.4.2 Algebraic reconstruction techniques ............. 26
2.4.3 Concepts for improved computational efficiency .. 27
2.4.4 Particle based iterative reconstruction ......... 29
2.5 Particle displacement estimation ....................... 31
2.6 Motion-based suppression of ghost particles ............ 33
3 Fast algebraic reconstruction for tomographic PIV ........... 35
3.1 Applied reconstruction techniques ...................... 36
3.1.1 The maximum entropy technique (MENT) ............ 36
3.1.2 The simultaneous multiplicative algebraic
reconstruction technique (SMART) ................ 39
3.1.3 The fast multiplicative algebraic
reconstruction technique (FMART) ................ 40
3.2 Numerical setup and data evaluation .................... 44
3.2.1 Synthetic images and flow field ................. 44
3.2.2 Procedure of quality evaluation ................. 46
3.3 Results ................................................ 49
3.3.1 Required number of iterations ................... 49
3.3.2 Ghost intensity suppression ..................... 51
3.3.3 Accuracy of particle position and of
displacement recovery ........................... 56
3.3.4 Reconstruction speed ............................ 62
3.4 Conclusions ............................................ 65
4 Studies on imaging and seeding in a transonic cascade ....... 67
4.1 The transonic cascade wind tunnel (TGK) ................ 68
4.2 Implementation of 2-C PIV .............................. 69
4.3 Assessment of tracer response and size ................. 72
4.4 Viewing geometry and laser energy requirements for
tomographic PIV ........................................ 77
5 Application of tomographic PIV to the high-speed corner
flow in a compressor cascade ................................ 81
5.1 Cascade geometry and flow parameter ................... 83
5.2 Optical setup .......................................... 84
5.2.1 Implementation of thick-sheet illumination ...... 84
5.2.2 Viewing geometry and imaging conditions ......... 87
5.3 Calibration technique and accuracy of image
registration ........................................... 88
5.4 Image evaluation ....................................... 90
5.4.1 Stereoscopic PIV evaluation ..................... 90
5.4.2 Tomographic particle volume reconstruction ...... 91
5.4.3 Particle displacement recovery .................. 93
5.5 Error analysis ......................................... 94
5.6 Discussion of results .................................. 98
5.7 Conclusions ........................................... 104
6 Feasibility study on tomographic spray shadowgraphy ........ 107
6.1 Modelling of droplet image formation .................. 109
6.2 Experimental setup of feasibility tests ............... 116
6.3 Implementation of camera calibration .................. 118
6.3.1 The effect of calibration marker type and
spacing on calibration accuracy ................ 119
6.3.2 The influence of the stage positioning errors
on calibration accuracy ........................ 122
6.3.3 Correction of stage positioning inaccuracies ... 123
6.4 Estimation of the smallest visible drop size .......... 126
6.5 Shadow image processing and volume reconstruction ..... 130
6.6 Reconstruction results ................................ 131
6.6.1 Instantaneous intensity distributions .......... 131
6.6.2 Averaged cross-sectional intensity
distributions .................................. 134
6.7 Discussion ............................................ 135
6.8 Summary ............................................... 136
7 Tomographic shadowgraphy of swirled spray injection in
a generic aero engine burner ............................... 139
7.1 Breakup of a plain liquid jet in cross flow ........... 140
7.2 Test facility and operation conditions ................ 142
7.3 Tomographic shadowgraphy setup for swirled fuel
sprays ................................................ 144
7.3.1 Compensation of optical aberrations imparted
by thick test rig windows ...................... 146
7.3.2 Camera calibration procedure ................... 148
7.3.3 Depth of field and smallest visible drop size .. 150
7.4 Image processing and volume reconstruction ............ 153
7.5 Droplet velocimetry by 3-D cross-correlation and
error analysis ........................................ 154
7.6 Results and discussion ................................ 155
7.7 Summary ............................................... 159
8 Conclusions and perspectives ............................... 161
8.1 Fast reconstruction of particle fields: performance
evaluation using synthetic data ....................... 161
8.2 Experimental performance evaluation in a transonic
cascade wind tunnel ................................... 162
8.3 3-D spray reconstructions using tomographic
shadowgraphy .......................................... 164
8.4 Perspectives .......................................... 165
A Camera calibration ......................................... 167
A.l Normalization of point correspondences ................ 167
A.2 Estimation of camera parameters ....................... 168
A.2.1 First order camera model (DLT) ................ 168
A.2.2 Higher order camera models .................... 169
Bibliography .................................................. 171
List of journal publications .................................. 191
Conferences ................................................... 194
|
|
