ng-Hyun Cho

Forces and Surface Pressure on a Blade Moving in Front of the Admission Region

The partial admission technique is widely used to control the output power of turbines. In some cases, it has more merits than full admission. However, additional losses, such as expansion, mixing, or pumping, are generated in partial admission as compared with full admission. Thus, an experiment was conducted in a linear cascade apparatus having a partial admission region in order to investigate the effect of partial admission on a blade row The admission region was formed by a spouting nozzle installed at the inlet of the linear cascade apparatus. Its cross section was rectangular and its size is 200 X200 mm 2 . The tested blade was axial-type and its chord was 200 mm. Nineteen identical blades were applied to the linear cascade for the partial admission experiment. The blades moved along the rotational direction in front of the admission region, and then operating forces and surface pressures on the blades were measured at the steady state. The experiment was conducted at a Reynolds number of 3 × 10 5 based on the chord. The nozzle flow angle was set to 65 deg with a solidity of 1.38 for performance test at the design point. In addition, another two different solidities of 1.25 and 1.67 were applied. From the experimental results, when the solidity was decreased, the maximum rotational force increased but the maximum axial force decreased.

Performance Characteristics of a Small-Scale Axial-Type Turbine Operated in a Low Partial Admission Rate

The performance characteristics of a partially admitted small-scale axial-type turbine, which could be applied to a driver of micro air grinders are experimentally studied with various nozzles, stators, and rotors. When air tools adopt axial-type turbines as drivers, they can operate without friction and abrasion because the turbine rotor does not make contact with the casing. In order to maintain these merits on a small-scale axial-type turbine without reducing power, performance characteristics are examined through measuring the specific output power and the net specific output torque with five different stators and with three different rotors and nozzles. The tested turbine consists of two stages and its mean radius of flow passage is 8.4 mm. The experimental results show that the improvement on the first stage is important to obtain the high specific output power because partially admitted flow is fully diffused in the second stage. Blade angles greatly influence the performance of a small-scale turbine operating in partial admission, and the optimal incidence angle is about 10.3°. At the fixed nozzle flow angle, the net specific output torque is varied by 15% by changing the rotor blade angle. Key W o r d s : Partial Admission, Micro-Turbine, Axial-Type Turbine, Turbine Performance, Air Tool.

A Study of the Design Technology for Developing a 100kW Class Steam Turbine

ABSTRACT Small scale steam turbines are used as mechanical drivers in chemical process plant or power generators. In this study, a design technology was developed for a 100kW class steam turbine which will be used for removing CO 2 from the emission gas on a reheated cycle system. This turbine is operated at a low inlet total pressure of 5 kgf/cm 2 . It consists of two stages and operates at the partial admission. For the meanline analysis, a performance prediction method was developed and it was validated through the performances on the operating small steam turbines which are using at plants. Their results showed that the output power was predicted within 10% deviation although the steam turbines adopted in this analysis were operated at different flow conditions and rotor size. The turbine blades was initially designed based on the computed results obtained from the meanline analysis. A supersonic nozzle was designed on the basis of the operating conditions of the turbine, and the first stage rotor was designed using a supersonic blade design method. The stator and second stage rotor was designed using design parameters for the blade profile. Finally, Those blades were iteratively modified from the flow structures obtained from the three-dimensional flow analysis to increase the turbine performance. The turbine rotor system was designed so that it could stably operate by 76% separation margin with tilting pad bearings.

An Experimental Study of the Performance Characteristics on a Multi-Stage Micro Turbine with Various Stages

An experimental study on an axial-type micro turbine which consists of maximum 6 stages is conducted to measure aerodynamic characteristics on each stage. This turbine has a 2.0 flow coefficient, 3.25 loading coefficient and 25.8mm mean diameter. The solidity of stators and rotors is within a 0.67~0.75, and the off-design performance is measured by changing the load after adjusting the mass flowrate and the total pressure to constant at inlet. A maximum specific output power of 2kW/kg/sec is obtained in one stage, but the increment of the specific output power with increasing stages is alleviated. In case of torque, the increment of the torque maintains to constant at low RPM region, but its increment become dull at high RPM region. The efficiency of the micro turbine becomes low because the tip gap effect is great due to the small blade, but it could be improved by increasing the stages.

A Study of Operating Forces on a Partially Admitted Turbine Blade

An experimental study has been conducted to analyze the operating forces on a partially admitted turbine blade using a linear cascade apparatus. Axial-type blades were used and the blade chord was 200mm. The rectangular nozzle was applied and its size was . The experiment was done at of Reynolds number based on the chord. The rotational force and axial force on the blade were measured at steady state by moving the blade to the rotational direction. The operating forces were measured at three different nozzle install angles of , and for off-design performance test. In addition, three different solidities of 1.25, 1.38 and 1.67 were applied. From the results, the maximum rotational force was increased when the solidity was decreased and the nozzle install angle was decreased. The axial force was increased by decreasing the nozzle install angle. The reverse axial force was obtained in the partially admitted region when the nozzle install angle was increased to .

A Study of Design Method of an Axial-Type Suction Fan

Many different types of fan have been applying to various industrial fields. Fan design methods are much different depending on the types of fan, operating conditions, and connecting parts at the inlet or exit of the fan etc. In this study, design methods for an axial-type suction fan are studied. This fan discharges the air in the relative static pressure of -285Pa to the atmosphere with the flow rate of . For three-dimensional blade design, three different design methods were applied, such as the free vortex method, the exponential method, and the cascade method. In the cascade method, the blade loading along the radial direction was obtained from the lift coefficient which was necessary to obtain the pressure rise on a fan rotor. This method is different from the free vortex and the exponential method which control the strength of the vortex. The fan performance prediction was conducted using the CFD with three different inlet ducts. The best fan performance was obtained when the fan was designed by using the cascade method. The designed fan using the exponential method showed better performance compared to a fan designed using the free vortex method. However, the fan performance was changed depending on the installed inlet ducts. So, an efficient fan can be designed with the adjustment of design variables on the basis of the flow structures within the fan as well as the fan design procedure.

Design of a 160% pitch passage for cascade experiments using optimization methods

A linear turbine cascade experimental apparatus often consists of only a few cascade blades. Advantages to this arrangement are increased from using larger cascade blades and easier optical access. However, fewer cascade blades in the cascade row make it difficult to establish periodic flow conditions between blades. In this study, a 160% pitch passage for cascade experiments with a single blade is designed to satisfy infinite cascade flow conditions without any flow control or tailboards. Fourteen geometric design variables are applied to the design of a 160% pitch passage by using a gradient-based optimization method and a genetic algorithm. Flow structures within a passage designed with a genetic algorithm are closer to the infinite cascade flow conditions than those obtained with a gradient-based method. The results show that infinite cascade flow conditions can be obtained by modifying only the passage walls of the cascade experimental apparatus.

Effect of the Suction Performance by the Air-Curtain Blowing around a Suction Duct

A study is conducted to improve the suction performance on suction devices which are used to remove polluted air generated by welding or machining process in a spacious working place of industry. Air-curtain is applied around the inlet of suction duct to interrupt the inflow of fresh air from the downstream region where is located opposite to the polluted air source. Two different air-curtain devices, such as a backward and a fully backward, are adopted. Suction region is experimentally investigated by measuring the suction velocities using a hot-wire anemometer. Contours of the suction velocity are compared with the computed results. The suction condition is selected to 110,000 Reynolds number which is widely used on typical suction devices, and a width of blowing passage for creating the air-curtain is chosen to 9.38% of the suction duct diameter. The experimental results show that the suction performance obtained with the backward air-curtain was better than that obtained with the fully backward air-curtain. On the suction duct using the backward air-curtain, the suction region estimated on basis of the 0.4m/sec is improved by 66% at the same input power.

Performance Characteristics of a Partially Admitted Small Mixed-Type Turbine

A mixed-type turbine was adopted and the rotor outer diameter was 108 mm. Turbine rotors were designed to the axial-type blade because the turbine operated at a low partial admission rate of 1.7-2.0% with two stages. Performance characteristics were studied when the spouting from the nozzle was toward radially inward or outward direction. Additionally, the effect at each stage of the rotor was measured. For comparing with each turbine performance, properties were measured based on various rotational speeds. Measured net specific torque was used to compare with the turbine system performance. On the mixed-type turbine, better performance was obtained when the operating air spouted toward radially inward direction. The specific torque was increased by 7.8% from using the second stage although its effect depended on the rotational speed.

A Study of the Tip Clearance Effect to the Performance of an Axial-Type Fan

Fan performances are obtained with various tip clearance gaps and stagger angles of the rotor. A tested fan is an axial-type fan of which the casing diameter is 806 mm. Two different rotors are applied to this test. One is designed on the basis of the free vortex method along the radial direction and the other is designed using the forced vortex method. The operating conditions are varied to the ultimate off-design point as well as the deign point. Overall efficiency, total pressure and input power are compared with the tip clearance gaps and different stagger angle. The experimental results show that changing of the stagger angle has minor influence to the performance when the same rotor is applied. When the tip clearance gap is less than 5% of the rotor span, the overall efficiency, total pressure loss and input power reduction are varied linearly with the variation of the tip clearance gaps. On the design point, the overall efficiency is decreased to the rate of 2.8-2.9 to the increasing of the tip clearance, but the changing rate of the overall efficiency is alleviated when the fan operates at off-design points. In particular, this rate is more quickly declined on a fan with the rotor designed using the forced vortex method. The result of the total pressure shows that the pressure reduction rate is a 0.08-0.1 according to the tip clearance, and additionally the input power reduction rate is a 0.045-0.065 at design point.