Mitsubishi Heavy Industries Technical Review Vol. 53 No. 4 (December 2016)
108

Development of Measurement Method for
Verification of Multi-Stage Axial Compressor
with Improved Performance

SATOSHI YAMASHITA*1

RYOSUKE MITO*2

MASAMITSU OKUZONO*3 SHINJI UENO*1

Gas turbine power generation systems are clean and economical power generation facilities
and have become more important because they are power generation facilities that can not only
meet the base load but also follow fluctuation of electric power demand under a background inrecent years where use of natural energy have expanded. Mitsubishi Heavy Industries, Ltd. (MHI)
is currently developing elemental technologies for 1700°C-class gas turbines as a projectsubsidized by the New Energy and Industrial Technology Development Organization (NEDO) withthe aim of further enhancement in the efficiency of gas turbines. For improvement in the efficiencyof the gas turbine cycle of axial flow compressors for 1700°C-class gas turbines, it is necessary toincrease the pressure ratio, enhance the performance and extend the stable application range. For
the verification of compressor performance, eight-stage compressor model test equipment wasdeveloped. This paper describes the developed test facility in the subsidized project and thedevelopment progress of a measurement technology to which a 3D metal printer is applied.

|1. Introduction
Gus turbines are required to further enhance their efficiency in order to reduce greenhousegas emissions and to extend their operability following fluctuations in electric power demand as
natural energy has been increasingly used in recent years(1). Gas turbine compressors are also
required to attain enhancement in their efficiency, an increase in the pressure ratio and an extensionof the operation range, and we are proceeding with research and development for all of theseareas(2)(3)(4).
MHI developed elemental technologies for 1700°C-class gas turbines under a subsidized
project of the Ministry of Economy, Trade, and Industry from fiscal 2004 to 2015, and have been
continuing the development as a NEDO project since fiscal 2016 in order to develop newtechnologies(5). For verifying the effects of the newly developed technologies in advance of theirapplication to actual machines and reflecting the results in the design of 1700°C-class gas turbines,
we developed an eight-stage axial flow compressor test facility.
For enhancement of the compressor performance, it is important to grasp the internal flow indetail. Such detailed internal flow measurement was executed with use of a test machine also in thepast. There was a concern with the conventional measurement method where the flow field wasdisturbed by the measurement equipment itself. Therefore we have developed a measurement
method that uses a 3D metal printer in order to minimize the effects on the internal flow.
The 3D printer technology has been developing rapidly in recent years, and is also being
increasingly applied to industrial gas turbines. 3D resin printers have been applied mainly to themanufacturing field as a tool for confirming the workability and assemblability in the design phase,
as well as for processing in order to reduce the development lead time(6)(7). In addition, research anddevelopment of 3D metal printers is moving forward, with the aim of using them to manufacturegas turbine parts. As a result, we used a 3D metal printer and machine processing simultaneously todevelop a compressor blade for measuring that contains a path for measurement. We applied the*1*2*3

Fluid Dynamics Research Department, Research & Innovation Center
Chief Staff Manager, Fluid Dynamics Research Department, Research & Innovation Center
Gas Turbine Technology Development Department, Turbine Technology Development Integration Division,
Mitsubishi Hitachi Power Systems,Ltd.

Mitsubishi Heavy Industries Technical Review Vol. 53 No. 4 (December 2016)109

3D printed measurement blade to a compressor test to measure the flow field in detail undertemperature and pressure conditions equivalent to an actual machine.
We used an eight-stage compressor that simulates the actual machine faithfully to implement
a surge test in advance of operation of the actual machine in order to confirm its integrity throughthe verification of the operation range. In addition, detailed measurement of the compressor internal
flow, which cannot be performed on an actual machine, and the verification of prediction accuracyof computer simulation (CFD: Computational Fluid Dynamics) were performed. This paper
presents the details thereof.

|2. Development of multi-stage axial flow compressor test facility
2.1

BackgroundAn axial flow compressor, one of the main components of a gas turbine, is a turbo machinewith multiple internal blades that rotate at a high speed to compress air, and therefore a complex
unsteady flow field occurs inside. 1700°C-class gas turbines are required to increase their pressure
ratio in order to improve the cycle efficiency. As the pressure ratio is increased, there is concern
over increased loss because of the development of a boundary layer, the decrease in the stable
operation range because of occurrence of reverse flow, separation, etc. and worsening of the startup
characteristics. It is necessary to develop new compressor technologies for suppressing thedevelopment of the boundary layer and the occurrence of reverse flow, separation, etc. in order toenhance the efficiency, extend the stable operation range and improve the startup characteristics,
while increasing the pressure ratio at the same time. We developed eight-stage axial flow
compressor test equipment in order to verify the new technologies in advance of their application toactual machines and reflect the technologies in the actual design.

2.2

Multi-stage axial flow compressor test facility

Inside an axial flow compressor, the boundary layer on the end wall grows in downstream
stages and causes blockage. A complex, unsteady flow field also occurs in the compressor becauseof this effect, such as interference between the blade rows, clocking (the difference of the stator
vane mounting position on each stage in the circumferential direction), etc., brought about by theadoption of the multi-stage system. Conventionally, small-sized test equipment that has a certain
number of extracted stages and is of a reduced scale was used for compressor verification tests.
Although MHI also fabricated three-stage and four-stage compressor test equipment to perform
verification tests in the past, it is necessary to implement verification tests using test machines withmore stages in order to perform the verification of the medium and rear stages that are believed tobe significantly affected by the upstream stages. Therefore, we fabricated an eight-stage test facility
in order to understand the detailed internal flow under the multi-stage conditions and verify theincrease in efficiency (Figure 1 and Table 1).
Table 1

Compressor design specification

Pressure ratio

Inlet Guide Vane (IGV ) + 8 stages(IGV and 1st to 3rd stator vane
is variable)
7.14

Rotating speed

14400 (rpm)Power demand

9100 (kW)StagesFigure 1

Eight-stage compressor rotor

When implementing the test for verifying the aerodynamic performance of an actualmachine, it is necessary to reduce the size of gaps including the rotor blade tip clearance according
to the scale ratio. Therefore, the scale ratio was set as large as possible in consideration of theassemblability. Also for making measurement easier, a larger scale ratio is desirable. As a result ofthe determination of the scale ratio in consideration of the assemblability and the ease ofmeasurement in this manner, the compressor power needed was approximately 9 MW. Because theMitsubishi Heavy Industries Technical Review Vol. 53 No. 4 (December 2016)110

largest power output of the existing motor is 4 MW, an air turbine was installed directly on thedownstream side of the compressor in order to cover the insufficient power amount of 5 MW andassist the motor power (Figure 2 and Table 2). The first stage stator vane of the turbine has avariable mechanism that drives and changes the stationary blade angle using an electric-powered
actuator. By changing the throat area of the first stage stationary blade of the turbine, the compressor
exit pressure can be adjusted and therefore the compressor test conditions can be set.
Table 2

Expansion ratio

3 stages(1st stator vane is variable)
6.72

Rotating speed

14400 (rpm)Power

6600 (kW)StagesFigure 2Turbine design specification

Power recovery turbine

The IGV and the first to third stage stator vanes were variable for which the angle can beadjusted individually by actuators. The compressor flow path had a bleeding chamber in order toverify the startup characteristics together with the variable stator vanes and then optimize thestartup schedule. In addition, an emergency blow-off valve was installed in the exit chamber of thecompressor. When the occurrence of a surge is detected by the pressure sensor installed on thecasing, the blow-off valve is automatically and instantly opened in order to release the pressure andcompressor from the surge condition. This allows a verification test of the compressor surge
tolerance to be implemented safely without causing damage to the facility.
These valves, variable stator vanes and rotation speed are computer-controlled using acontrol device similar to that used for the control of power plants that MHI built. The automatic
operation control following a pre-programmed operating schedule allows the easy setting of test
conditions and the implementing of a test that faithfully simulated the operating conditions of a
1700°C-class gas turbine compressor. In addition, the control device always monitors operating
conditions at various points of the test machine including the air temperature, air pressure, vibrationof the axis, etc., as well as the operating conditions of auxiliary equipment including lubricating oilpressure, cooling air, cooling water, etc. The control device issues an alarm when an abnormality
occurs with the test facility and trips and stops the machine when a limitation value is reached. This
provides protection for the test facility and saves labor in the monitoring of operations during a test.

2.3

Measuring blade made with a 3D printerThere are multiple measuring points inside the compressor provided in order to understandthe internal flow of the compressor in detail. In the past, typical internal flow measuring methods
included wired pressure conduits or sensors that were attached to the blade, probes that wereinserted into the flow path, etc. The wiring of the conduits or sensors on a blade surface caused thedeformation of the blade and the disturbance of the internal flow. The insertion of a probe brought
about the disturbance of the flow field caused by the probe itself and resulted in increased
measuring error. With such a background, we installed a measuring blade made with a 3D metal
printer in order to keep the effects on the internal flow field as small as possible while obtaining
detailed internal flow data. The pressure was measured in the pressure measurement through-holewith a diameter of 0.4 mm drilled on the very thin compressor stator vanes with a thickness ofapproximately 1.5 mm. In addition, a hole with a diameter of 0.7 mm was provided on the blade inorder to accommodate the thermocouple with a diameter of 0.5 mm for temperature measurement.
The compressor blade had a three-dimensional shape for improved performance. A model that hadmeasurement holes three-dimensionally following the blade shape was designed using 3D CAD

Mitsubishi Heavy Industries Technical Review Vol. 53 No. 4 (December 2016)
111(Computer Aided Design) and formed with a 3D metal printer. In this manner, accommodation forpressure holes and temperature measurement could be provided inside the blade (Figure 3).
The stator vanes of the compressor test machine experience stress equivalent to an actualmachine. The 3D printed measurement blade was strength-tested and its strength was confirmed tobe equal to the conventional blade material before the application of the measuring blade to the test
machine.

Figure 3

Static pressure measurement blade made with a 3D printer(used as a set of two blades at three measurement points on each of the leading and trailing edge)

2.4

Test results

A test of the compressor was carried out and its overall performance was obtained(Figure 4). In addition, a verification test of the compressor surge tolerance that simulated a partial
load operation was carried out to confirm that the surge tolerance was sufficient. The integrity andreliability of the compressor within the gas turbine operating range was verified and confirmed.

N*: Corrected mass flow

Figure 4 Compressor overall performance

The pressure and temperature at various stages were measured using a 3D printed
measurement blade. It was confirmed that the load balance in each stage of the compressor and thedistribution over the height direction was as expected (Figure 5 and Figure 6).
The pressure distribution on the blade surface was understood in detail using the 3D printed
measurement blade that had pressure measurement holes on the blade surface. The pressure
distribution of the compressor blade surface in a partial load operation was measured andseparation from the blade surface before the occurrence of a surge was confirmed throughcalculation (Figure 7). The presence or absence of separation from the blade surface is an
important factor that determines the stable operation range of the compressor, but its prediction isdifficult. The timing of separation from the blade roughly conformed to the results of CFD
prediction and its prediction accuracy was confirmed.
The verification data obtained through this test will be used to improve CFD analysis codes
in order to further enhance CFD prediction accuracy and will be applied to the development of1700°C-class compressors.

Mitsubishi Heavy Industries Technical Review Vol. 53 No. 4 (December 2016)
112

Figure 5

Stage pressure ratio

Figure 6 Leading edge total pressure and wall pressureof measurement blade made with 3D printerFigure 7 Compressor map and fourth stator surface static pressure at surge test

Mitsubishi Heavy Industries Technical Review Vol. 53 No. 4 (December 2016)113|3. Conclusion
We developed an eight-stage test facility and executed an actual machine verification test. Inaddition, we applied a 3D printer to make a measuring blade for obtaining detailed internal flow
data. The obtained data will be reflected on design of next-generation compressors. The description
in this paper is part of the development of compressors for 1700°C-class gas turbines. In addition,technologies for improved performance aiming at practical application are being developed, andverification tests will be implemented continuously using the eight-stage axial flow compressor testequipment. The obtained results will be reflected in the design of 1700°C-class gas turbines forapplication to an actual machine. We are committed to contributing to the resolution of energy
problems and global environmental problems through the diffusion of the latest gas turbine
combined cycle power generation technologies.

References
1.
2.
3.

4.
5.
6.
7.

Masada, J. et al., Development and Current Status of Turbine Aerodynamics for Industrial Gas Turbine,
Japan Society of Mechanical Engineers Vol. 119 No. 1173 (2016) pp. 2-5Outa, E. et al., Development and Current Status of the Compressors for Industrial Gas Turbines, Japan
Society of Mechanical Engineers, Vol. 119 No. 1173 (2016) pp. 6-9Mito, R. et al., Computational Fluid Dynamics Technology Applied to High Performance, Reliable Axial
Compressors for Power Generation Gas Turbines, Mitsubishi Heavy Industries Technical Review Vol. 52
No. 1 (2015) pp. 1-7Gao X. et al., Numerical and Experimental Investigation on the Effect of Tip Clearance Multi-Stage AxialCompressor, IGTC 2015, Tokyo, Japan
Ito, E. et al., Key Technologies for Ultra-High Temperature Gas Turbines, Mitsubishi Heavy Industries
Technical Review Vol. 52 No. 2 (2015) pp. 15-31
Komaki, T. et al., 3D printer use cases for industrial gas turbine, Journal Of The Gas Turbine Society Of
Japan Vol. 42 (2016) pp. 439-442
Haraguchi, H., Practical use of 3D Printer for MHI, Japan Society of Mechanical Engineers Vol. 118 No.
1154 (2015) pp.40-41