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DEVELOPMENT OF SMALL SIZE PNEUMATIC MACHINES WITH TURBINE DRIVE GEARS
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DEVELOPMENT OF SMALL SIZE PNEUMATIC MACHINES WITH TURBINE DRIVE GEARS

 

Research refers to small size turbine gears oriented for driving high speed pneumatic tools. Unique testing equipment and new approach to study turbine drive gears, developed method of turbine blade crowns profiling and unique aerodynamic configurations of turbine stages are described in the paper.

 

 

1. DEVELOPMENT STRATEGY

 

Turbine drive gears with outer diameter up to 4” are widely utilized in cryogenic plants, in auxiliary gears of aircraft and submarines, in pneumatic tools and so on. Small size turbines differ from regular ones, first and foremost, with aerodynamic configuration of their stages. Thus, axial turbines oriented for application in pneumatic tools, possess the following distinguishing features:

·       Relatively big axial gap between nozzle diaphragm and turbine wheel

·       Relatively thick edges and small heights of nozzles and working blades

·       Relatively big angular length of the nozzles (up to 30°).

 

Working fluid into axial turbines, having three-dimensional structure, yields to modeling and computation very poorly. Moreover, turbine’s nozzle channels have very little square area that renders impossible to study structure of the gas stream by measuring its local parameters. Thus, study and modeling turbine drive gears should be based on measuring turbines’ generalized characteristics, namely: gas consumption, working fluid angles, power, torque, efficiency and frequency. In additional, visualization of the working fluid [1] should be considered to be the most accessible and adequate method of flow structure research.

 

Goals of the research were the following:

·       Development of new method for study small size turbine stages

·       Design and approbation of special equipment for testing turbines

·       Obtaining primary information of working fluid structure into turbine blade crowns

·       Increasing aerodynamic efficiency of small size turbine stages

·       Development of effective turbine drive gears for pneumatic tools.

 

 

2. TESTING EQUIPMENT

 

Relatively little values of measuring characteristics require to apply special approaches to development of testing equipment. The described testing device (see photo in fig. 1) operates with compressed air system and includes three main units, namely:

·       Unit of investigated turbine stage with assembly for working fluid visualization

·       Unit of loading drive gear with assembly for measuring of turbine’s torque

·       Unit for measuring parameters of nozzles.

 


                                                                                               Fig. 1. Testing device

 

Unit of investigated turbine stage includes receiver 1 (see scheme in fig. 2) with inlet branch pipe 3. Investigated turbine’s nozzles diaphragm 2 is fixed into the receiver. Visualization of the working fluid is realized by flow coloration in assembly 4, which is placed in the intake of the nozzles. Coloring substance is formed by burning of special material on electrical incandescence filament 5. Pipes 6 and nets 7 form axial direction of the gas stream at the intake of the nozzles.

 


                                                                                    Fig. 2. Scheme of testing device

 

Loading of the investigated turbine stage is conducted by the unit having reverse rotation turbine drive gear. Its nozzle diaphragm 8 is fixed into receiver 9. The receiver is placed into bushing 10 with gas static support which removes mechanical friction between them. Compressed air enters the receiver 9 in centripetal direction as a “free stream” through branch pipe 12. At the same time, air enters the bushing 10 for gas static support through branch pipes 11. Labyrinth packing 13 separates two these gas streams. Working fluid leaves the reverse rotation turbine drive gear through device 14 in centrifugal direction. Torque on the nozzle diaphragm 8 is measuring by device 15. Rotor 19 with roller 16 is fixed in the receiver 9. Wheels of both turbine stages 17 and 18 are fixed in ends of the roller (see photo in fig. 3).

 


                                                                                                              Fig. 3. Rotor support assembly

 

Unit for measuring parameters of nozzles, being able to operate jointly with describe above unit of loading drive gear, has similar design with it (see photo in fig. 4). In this unit nozzle diaphragm 3 (see scheme in fig. 5) of the investigated turbine is fixed into the receiver 2. The receiver is placed into bushing 1 with gas static support which removes mechanical friction between them. Compressed air enters the receiver with the nozzle diaphragm in centripetal direction as a “free stream” through branch pipe 5. At the same time, air enters the bushing 1 for gas static support through branch pipes 4. Labyrinth packing 6 separates two these gas streams.  Pipes 7 and nets 8 form axial direction of the gas stream at the intake of the nozzles. Torque of the nozzle diaphragm is measuring by device 9, axial force – by device 10. The obtaining characteristics enable to calculate a value of effective fluid angle in the exit from the investigated nozzle diaphragm.

 


  

                                                                                         Fig. 4. Unit of loading drive gear

 


                                                                    Fig. 5. Scheme of unit for measuring parameters of nozzles

 

 

3. VISUALIZATION OF WORKING FLUID IN SMALL AXIAL TURBINE STAGE

 

Visual research of the working fluid into axial turbines based on pictures, left by colored gas on outer cylindrical surfaces of the stages. First group of the investigated nozzle crowns was designed according to regular methods of blade crowns profiling. As the working fluid visualization indicated, a smooth flow took place into the nozzles only at subsonic pressure ratio (see picture of flow visualization into the nozzles diaphragm, having outer diameter equal to 1.5”, in fig. 6). However, the working fluid had an evident non-stable character with strong fluctuations at supersonic ratio. Effective angle of the gas flow exceeded the geometrical angle of nozzles’ outlet sections to 3…6 times. Level of efficiency of these turbines at P0/P1=5 was very low.

 


                                                          Fig. 6. Visual picture of working fluid into regular nozzles diaphragm

 

On the basis of analyzing obtaining information, we decided to improve aerodynamics of supersonic nozzles blades by enforcing their directional influence (see drawings and photo in fig. 7). Working fluid into the developed nozzles with straightforward blades’ outlet portions (see picture of flow visualization into the nozzles diaphragm, having outer diameter equal to 1.5”, in fig. 8) seemed essentially better at P0/P1=5, than into regular ones (fig. 6). Application of the method of nozzle blades profiling increased efficiency of small size turbine stages by 10-20%.

 

                                                                            a)


                                                                                b)


                                                                                        c)


                         Fig. 7. Nozzle diaphragms with outer diameter equal to 1.5” having straightforward blades’ outlet portions:

                     a) Axial supersonic nozzle blade profile (dimensions in millimeters)

                     b) The most efficient nozzle blade crown (dimensions in millimeters)

                     c) Tested nozzle diaphragms with various geometrical parameters

 


                                             Fig. 8. Visual picture of working fluid into developed nozzles diaphragm at P0/P1=5

 

Study of working fluid into partial turbines was conducted by visual research of stages, having outer diameter equal to 1.5”, with motionless turbine wheels (see visual picture in fig. 9) and without them (see visual picture in fig. 10). The following things were quite clearly discerned in these pictures:

·       Borders of the flow at the outlet sides of the nozzle diaphragm and the turbine wheel

·       Local leaps of pressure and secondary flows in the gap between the nozzle diaphragm and the turbine wheel.

 


                                     Fig. 9. Visual picture of working fluid into partial turbine stage at P0/P1=5 (ε – rate of partiality)

 


                                                                     Fig. 10. Visual picture of working fluid into partial nozzles

 

It was established that effective arc length of the working fluid was more, than total geometrical arc length of the nozzles, approximately to 15…20%. The value of working fluid angle mainly depended on the pressure ratio. Flow borders had a form of a cone with a great angle of opening which reaches a value of 60° at P0/P1=5.

 

Several actions for improvement of partial turbines were developed and conducted. Thus, changing geometrical angles of extreme nozzle channels, which were placed at the boundaries of active arc zone, reduced energy losses by 5-10%. Moreover, visual experiments enabled to introduce essential corrections to methods of calculation and optimization of turbine aerodynamic characteristics.

 

 

4. MANUAL PNEUMATIC MACHINES WITH TURBINE DRIVE GEARS

 

Results of our work study were successfully applied in small size turbine stages for various purposes. The presented work concerns turbine drive gears for pneumatic tools. To describe these machines, we named them as the following: TINY SIZE MACHINE, SMALL SIZE MACHINE and REGULAR SIZE MACHINE.

 

 

4.1. TINY SIZE MACHINE

 

Drive gear of Patent [2] was developed for application in tiny size manual pneumatic tools. The above described method of blades profiling was applied at design of the turbine stage. As it is seem in the scheme (fig. 11), nozzle channel 7 of the developed turbine has straightforward outlet portion for enforcing its directional influence. Drive gear includes nozzle diaphragm 2 which has a form of a ring being placed inside back casing 1. Inlet assembly is placed inside the nozzle diaphragm. The assembly includes hole 3 in its cylindrical wall for working fluid entrance. The hole is placed opposite intake portion of the nozzle. The nozzle diaphragm possesses ability to tangential movement relatively the hole in order to gas consumption adjustment. Rotor 6 with axial turbine wheel 4 is placed inside front casing 5.

 


                                                                        Fig. 11. Scheme of turbine drive gear for tiny size tools

 

Working fluid enters the nozzle diaphragm through the hole 3 in centrifugal direction. The direction of the flow is changed inside the intake portion of the nozzle. Fluid continues its movement axially through outlet portion of the nozzle and working blade crown of the turbine wheel. Advantage of this design is the following:

·       Compact centrifugal entrance of the working fluid to the turbine stage through inside part of the nozzle diaphragm combined with axial flow exit from the stage  

·       Combination of gas consumption regulator and nozzle diaphragm as an integral unit.  

 

Characteristics of the tiny size machine are the following:

·       Weight – 0.09 kg, maximal outer diameter – 0.95” and casing length – 4”

·       Power – about 100 Wt at inlet air pressure equals to 6 At

·       Idling frequency (in no-load operation) – 120,000-150,000 rpm.

 

 

4.2. SMALL AND REGULAR SIZE MACHINES

 

Double rimmed turbine stages possess the acceptable aerodynamic characteristics, including idling frequency and torque, for application in small and regular size manual pneumatic tools. However, having big energy losses, axial double rimmed turbines can’t satisfy to required level of efficiency. Moreover, these stages have big rotating mass, causing high level of vibration, big length and bad adaptability to manufacturing.

 

To solve these problems, radial double rimmed centrifugal-centripetal turbine was developed. Drive gear of Patent [3] includes (see scheme in fig. 12) back casing with inlet assembly for gas consumption adjustment and centrifugal nozzle diaphragm 2; front casing with double rimmed turbine wheel 1 and directing diaphragm 5. The turbine wheel has centrifugal (first) working blade crown 3 placed on its back side and centripetal (second) working blade crown 4 placed on its front side. The directing diaphragm has axial blade crown. The inlet assembly is placed inside the nozzle diaphragm.

 


                                                              Fig. 12. Scheme of turbine drive gear for small and regular size tools

 

Working fluid enters the nozzle diaphragm in centrifugal direction. Then it passes the first working blade crown 3. Flow direction is changed to axial one in front of the directing diaphragm. Passing its blade crown, the working fluid changed direction again. Turning from axial direction to centripetal one the flow continues its movement through second working blade crown 4. The working fluid leaves the stage moving axially. Advantages of this design are the following:

·       Compact centrifugal entrance of working fluid to the turbine stage through inside part of the nozzle diaphragm combined with axial flow exit from the stage

·       Arrangement of two working blade crowns on one integral turbine wheel.

 

The developed drive gear has little rotating mass and low level of vibration. Acceptable level of turbine efficiency causes by two-dimensional structure of the working fluid without essential energy losses. The machine is very cheap at mass production because almost all its parts may be made by casting.

 

Characteristics of the small size machine (fig. 13) are the following:

·       Weight – 0.12 kg, maximal outer diameter – 1.4” and casing length – 4.2”

·       Power – about 200 Wt at inlet air pressure equals to 6 At

·       Idling frequency (in no-load operation) – 80,000-100,000 rpm.

 


                                                       Fig. 13. Manual pneumatic small size machine

 

Characteristics of the regular size machine (fig. 14) are the following:

·       Weight – 0.35 kg, maximal outer diameter – 2.1” and casing length – 4.7”

·       Power – about 500 Wt at inlet air pressure equals to 6 At

·       Idling frequency (in no-load operation) – 50,000-60,000 rpm

 


                                                                             Fig. 14. Manual pneumatic regular size machine

 

 

4.3. PROSPECTIVE TURBINE DRIVE GEAR

 

The prospective turbine of Patent [4] differs from described above double rimmed stage (fig. 12) only with design of its outlet section. Inlet assembly, nozzle diaphragm, first working blade crown and directing diaphragm have similar aerodynamic configuration in both stages. Difference is the following: second working blade crown is placed on cylindrical surface of turbine wheel opposite axial blade crown in this design (see photo in fig. 15). Working fluid passes the first working blade crown centrifugally. Flow direction is changed to axial one in front of the directing diaphragm. Then the fluid passes the stage, moving axially through directing diaphragm and second working blade crown of turbine wheel.

 


                                                                       Fig. 15. Structural elements of double rimmed turbine stage

 

 

5. CONCLUSION

 

The developed testing equipment enabled to measure small turbine’s generalized characteristics and conduct visual research of working fluid structure. The described method of study of turbines’ aerodynamics may be widely utilized for improvement of blade crowns, analysis and mathematical modeling of the fluid structure in turbine stages. As a result of our work, principles of the design of high efficient turbine stages were developed.

The described turbine drive gears include high efficient blade crowns and unique aerodynamic configurations of turbine stages. Tests of the developed machines revealed that they outmatched existent pneumatic drive gears with balance of efficiency, air consumption and power. Consumer appeal of our pneumatic machines is also conditioned due to their convenience for operation and manufacturing. The developed manual pneumatic tools may be utilized in steel manufacturing, molding and denture production for grinding and polishing operations.

 

 

5. ABOUT US

 

Scientific Group on Turbine Aerodynamics has been working for Power Units and Heat Engines Department of Nizhniy Novgorod State Technical University (Russia). We have been engaging in research of small size turbines and development of high speed drive gears for about 20 years. Our current activity orients to development and serialize of manual pneumatic tools. To succeed in this deal, we are working in cooperation with the Company called “Formula” which possesses manufacturing facilities and widen experience in mass production of precision gears.

 

We hope the results of our research would interest specialists in the fields of applied aerodynamics and development of small size turbine drive gears. We suppose that our experience, skills and knowledge could be proposed for international cooperation.

 

 

REFERENCE

 

1. Visotina V. and others, 1984, “Visualization of sub-sound fluid in radial-axis channel”, Collection of paper Moscow Energetic Institute., Moscow, No. 623, pp. 60-68, Russia

2. A. Tchouvakov, 2003. Inlet Assembly for Axial Turbine: Patent of Israel No. 138482  

3. Y. Kuznetsov, A. Tchouvakov, P. Semashco, 2003. Multi-Rimmed Radial Turbine: Patent of Russia No. 34643

4. Y. Kuznetsov, A. Tchouvakov, P. Semashco, 2003. Double Rimmed Turbine: Patent of Russia No. 34644

 

 

Yuriy Kuznsov, Dr. Sc. in Techniques, Professor

Alexander Tchouvakov, Ph.D. in Techniques

Vladimir Himich, Dr. Sc. in Techniques, Professor

 

State Technical University of Nizhniy Novgorod, Russia

Department of Power Units and Heat Engines

 

 

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