SOME STUDIES OF FLOW THROUGH INWARD FLOW RADIAL CASCADE
BY
B.D.PATHAK
A THESIS SUBMITTED
IN FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
Lv4%
TO THE
INDIAN INSTITUTE OF TECHNOLOGY, DELHI INDIA
JANUARY, 1990
I. T. DEL1-it.
LIIRARY
4ee. 140711.-.2-?.1
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CERTIFICATE
This is to certify that the thesis entitled "Some studies of flow through inward flow radial cascade" being submitted by Mr.B.D.Pathak to the Indian Institute of Technology, Delhi, for the award of the degree of Doctor of Philosophy in Mechanical Engineering is a record of bonafide research work carried out by him. He has worked under our guidance and supervision and fulfilled the requirement for the submission of this thesis which to our knowledge, has reached the requisite standard.The results contained in this thesis have not been submitted, in part or in full, to any University or Institute for the award of any degree or diploma.
--7
(Dr. S M Yahya) (Dr. Lajpat Rai) Professor Assistant Professor
Department of Mechanical Engineering Indian Institute of Technology, Delhi
Hauz Khas, New Delhi--110016
ACKNOWLEDGEMENT
The author expresses his sincere gratitude and appreciation to Prof.S M Yahya and Dr.Lajpat Rai under whose inspiring guidance this work was done. The author is indebted to them for encouragement, involvement, valuable suggestions and moral support throughout the period of this work. He will always be inspired by their great humanly qualities and moral values.
The author is thankful to Prcf.D P Agrawal, Professor, Department of Mechanical Engineering I I T Delhi for the help obtained from the Turbomachinery Laboratory.
The author benefited greatly from the lively discussions with him during the course of experimentation. The author records his thanks to Prof. E L Elder, Head, Turbomachinery Research Group, Cranfield Institute of Technology U.K., and Dr. N C Bains Lecturer in Mechanical Engineering, Imperial College of Science, Technology and medicine, London, for their suggestions and fruitful discussions during the period of this research work.
The cooperation and help from the staff of Turbomachinery Laboratory, Mechanical Engineering workshop, I D D C are gratefully acknowledged. The author thanks them for the skillful work done in fabricating the experimental set-up.
Thanks are also due to the Principal, Delhi College of Engineering, Delhi for the sponsorship of PhD program under QIP. The help, encouragement and support from faculty members, fellow research scholars, colleagues and others are, also duly acknowledged.
(B D PATHAK) ii
ABSTRACT
Inward flow radial cascades are installed in radial turbomachines to change the circulation of inward flow in the fixed channels. These cascades are used as guide blades in water and gas turbines. The performance of radial inflow turbines matches the performance of axial flow turbines with the added advantages of cost saving and reletively low tip--clearance 'sensitoVity. With their application for turbocharging and small power generation, there is a renewed interest in the field of inward flow radial turbines in these and other application categories.
The present investigation was undertaken to study and analyze the flow in an inward flow-radial cascade over a wide range of operational parameters. With this objective in mind, the test facility was designed to conduct experiments for aspect ratios of 0.1,0.2, 0.3, and 0.5.
For each of these aspect ratios, tests were perfoLmed at blade trailing edge angles of 65°, 70° and 80° ( measured from radial direction ). The Reynolds number was varied upto capacity limit of a blower that is driving air though the test rig. The flow parameters in the blade channel were measured by using a calibrated pitot-static yawmeter.
The experimental results show the incidence effect on blade pressure-side. The stall patches are seen near the
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blade pressure-side leading edge and suction-side trailing edge. The flow inside the blade channel shows an overturning effect due to the pressure variation from blade pressure to blade suction-side with a higher overturning in low aspect ratio cascades. The exit flow angle decreases with the increase of Reynolds number because of the increase in pressure in the radial direction radial pressure and decreases with the increase of aspect ratio. The blade boundary layers and side-wall boundary layers fill the blade channel exit cross-section. Wide wakes are seen at the cascade exit section. The side-wall boundary layers are strongly affected by secondary flows. Two high loss zones are formed near the side-wall corners near the blade suction side. These show the presence of leading edge vortices with a stronger vortex leg near the shroud side. The passage vortices are entirely absent. The loss coefficient is greater for smaller aspect ratio cascades and larger blade angle setting.
CERTIFICATE
ACKNOWLEDGEMENT ii
ABSTRACT ii
CONTENTS
NOMENCLATURE xi
CHAPTER I INTRODUCTION 1- 1.1 Classification of Inward Flow Cascades 3
1.1.1 Vaneless Nozzles 3 1.1.2 Vaned Nozzles 4 1.1.2.1 Uncambered Blades 5 1.1.2.2 Cambered Blades 5 1.1.3 Tandem Cascade 6 1.2 Flow process in an inward flow nozzle cascade 7 1.3 Performance Coefficients 7 1.3.1 Nozzle Pressure Loss Coefficient 8 1.3.2 Static enthalpy loss coefficient 9 1.3.3 Nozzle efficiency 9 1.4 Design and Performance parameters 10
1.4.1 Geometric Parameters 11 1.4.1.1 Blade thickness/chord ratio 11 1.4.1.2 Leading edge thickness 11 1.4.1.3 Trailing edge thickness 11 1.4.1.4 Camber and Stagger angle 12 1.4.1.5 Aspect Ratio 12 1.4.1.6 Effect of blade spacing 12 1.4.2 Aerodynamic Parameters 13
1.4.2.1 Incidence Angle 13 1.4.2.2. Reynolds Number 13 1.4.2.3. Free Stream Turbulence Level 14 1.4.2.4. Surface Roughness 15 1.5 Scope of the Present Work 15
1.6 Outline of the Thesis 17
CHAPTER-II LITERATURE REVIEW 18-51
2.1 Introduction 18
2.2 Experimental Investigations 19 2.2.1 Nozzle blade shape 24 2.2.2. Losses in nozzle cascade 26 2.2.3 Exit flow angle 31 2.2.4 Secondary Flows 36 2.2.5 Flow Visualization Studies 38 2.3 Theoretical Studies and Computation Methods 38 2.3.1 Method of conformal Transformation 43 2.3.2 Method of Singularity 44 2.3.3 Streamline Curvature Method 46 2.3.4 Stream Function Method 47 2.3.5 Potential Function Method 48
CHAPTER-III EXPERIMENTAL SET UP AND INSTRUMENTATION 52-71
3.1 Air supply unit 52
3.2 Test section 54
3.2.1 Guide blades 56 v
i
3.3 Instrumentation 57 3.3.1 Pitot-static Yawmeter (Cobra Probe) 58 3.3.1.1 Construction 58 3.3.1.2 Probe traversing mechanism 60 3.3.1.3 Probe calibration 60
3.4 Manometers 62
3.4.1 Micromanometer 63 3.5 Instrumented blades 63 3.6 Flow Channel Measurements 65 3.6.1 Pressure measurements 66 3.6.2 Flow angle measurements 62 PLATE 3.1 EXPERIMENTAL SET-UP 69 PLATE 3.2 GUIDE BLADES AND CASCADE BLADE RING 69
PLATE 3.3 TEST RIG 70
PLATE 3.4 TEST RIG (INSIDE VIEW) 70 PLATE 3.5 TRAVERSING ARRANGEMENT 71 PLATE 3.6 MICROMETER AND INCLINED-TUBE MANOMETER 71
CHAPTER - IV EXPERIMENTATION AND DATA PROCESSING 72.
4.1 Introduction 72
4.2 Operating Parameters 73 4.3 Preliminary Experiments 75 4.4 Main Experimental Investigations 77 4.5 Experimental procedure 78 4.6 Flow visualization by Tufts 81
4.7 Data Processing 82
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i
4.8 Sources of Error 8;
4.9 Uncertainty Analysis 89
TABLE 4.1 ESTIMATED UNCERTAINTY INTERVAL FOR MEASURED
QUANTITIES 87
CHAPTER V 5.1
5.2
RESULTS AND DISCUSSIONS 88-122
Quality of Flow entering the cascade 89 5.1.1 Velocity and flow angle profiles in
axial direction 90
5.1.2 Velocity and flow angle profiles in
circumferential direction 91 Flow field in the cascade channel 91 5.2.1 Velocity distributions 92 5.2.1.1 Effect of Reynolds number 94 5.2.1.2 Flow channel velocity contours 94 5.2.1.3 Exit section velocity distribution 95 5.2.2 Flow Angle Distribution 96 5.2.2.1 Reynolds number effect 98 5.2.2.2 Flow angle contours 10(
5.2.2.3 Exit section flow angle
distribution 101
5.2.3 Static pressure distribution 101
5.2.3.1 Reynolds number effect 103 5.2.3.2 Static pressure contours 103 5.2.3.3 Exit section static pressure
distribution 104
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5.2.4 Stagnation pressure distribution 105 5.2.4.1 Reynolds number effect 107 5.2.4.2 Stagnation pressure contours 107 5.2.4.3 Exit section stagnation pressure
distribution 108
5.3 Blade Surface Static Pressure Variation 109 5.3.1 Mid-span pressure variations 110 5.3.2 Static pressure variation with blade
height 111
5.3.3 Blade surface static pressure contours 112 5.4 Side-walls Static Pressure Distribution 113 5.5 Flow in vaneless space 115 5.5.1 Velocity variation 115 5.5.2 Flow angle variation 116 5.5.3 Static pressure variation 116 5.5.4 Stagnation pressure variation 117
5.6 Flow visualization 117
5.7 Nozzle cascade performance 118 5.7.1 Loss coefficient variation 119
5.7.1.1 Loss coefficient variation with
Aspect Ratio 120
5.7.1.2 Loss coefficient variation with
cascade Blade angle 121 5.7.2 Flow angle variation 121
5.7.2.1 Flow angle variation with cascade
Blade angle 121
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5.7.2.2 Flow angle variation with Aspect
ratio 122
CHAPTER VI CONCLUSIONS AND SUGGESTIONS FOR FUTURE WORK 123-1
6.1 Conclusions 123
6.2 Suggestions for future work 126
REFERENCES 127-1
APPENDIX A 140
APPENDIX B 142
APPENDIX C 143
FIGURES 144- 238
