MEASUREMENTS IN THE VT 400 AIR TURBINE

. This paper presents a basic description of measurements on the experimental air turbine located in the laboratories of the Department of Power System Engineering (KKE). The research on this turbine focuses on the ﬂow in a one-stage air turbine. It monitors the inﬂuence of the spatial formation of the blades on the eﬃciency of the stage. A new geometry with reaction blading is currently being tested. This work has been carried out in cooperation with an industrial partner, Doosan Skoda Power (DSPW).


Introduction
Steam turbine constructers consider the methodology and the rules for calculating blading efficiency, when designing turbine stages, to be one of the most valuable and most confidential parts of their know-how.Guaranteed efficiency values are one of the key factors in the competition to retain and gain customers.Obtaining new data for specifying the so-called efficiency prediction, and also research focused on optimizing efficiency prediction, are important long-term development objectives for all steam turbine producers.Generally, blade spatial forming is one of the main instruments for increasing blading efficiency.It focuses particularly on reducing the influence of so-called secondary flow and related losses, but also deals with targeted redistribution of particular flow parameters, not only along the length of the blades, but also within the stage, or indeed within the whole flow section.

Cooperation on the development of blading
Doosan Skoda Power (DSPW) has engaged in intense development of new types of blading in recent years, and cooperation with the Department of Power System Engineering (KKE) has been an integral aspect of this development work.Between 2000 and 2005, the development work aimed at forming stationary blades.Variants with both lean and compound lean peripheral inclination, and also a controlled flow blade, were investigated (see Figure 1).These types of blading were tested on a SKODA 1MW trial steam turbine, and simultaneous tests were carried out on the KKE air turbine at the University of West Bohemia in Pilsen.
The studies concentrated on forming stator blades, while preserving the original prismatic moving blades.One of the outcomes of the research, which was carried out within the framework of several grant-funded projects (FD-K/0111 , GA101/01/14482 ), was the design by DSPW of the so-called banana blade.Some results of the cooperation between DSPW and KKE have been presented, e.g. in [1][2][3][4].
In the following period, DSPW, a traditional producer of action conception turbines, began to develop 3D blading with so-called slightly increased hub reaction.This blading included the formation of both stationary blades and moving blades.
Compound lean blading, combined with controlled flow access of stationary blades, supplemented by an appropriately formed (twisted) moving blade, was designed and tested within the framework of grantfunded projects (e.g.FT-TA/0853 , FT-TA2/0374 , FT-TA5/0675 ) and ongoing cooperation.Experimental testing of these "Full3D" stages was one of the principal topics of the cooperation between KKE, a university department, and DSPW, an industrial company, between 2008 and 2012.Three variants with different compactness of the blades were tested stepwise (Figure 2).The results were published for example in [5][6][7][8][9].This development raised the efficiency by approx. 2 % in the HP component and by 1.5 % in the MP component, in comparison with classic prismatic or warped blading.In many cases, improved design principles have been transferred into practical applications.
Stages with an increased hub reaction basically represent a developmental transition between action and reaction stage conceptions.Current developments in 3D blading have been leading DSPW logically to-  However, the development trends and objectives of individual competing companies have not been focused and profiled only on action blading or reaction blading.Much work is also being done on so-called variable reaction stages, i.e. the optimized use of blades with a different reaction, with regard to the design requirements and attempts to achieve higher efficiency.This is a present-day developmental direction at DSPW, and it foms the topic of a follow-up internal project, where the application of reaction blades to high efficiency turbines is also being investigated.

Experimental air turbine at KKE
The experimental air turbine at KKE is a single-stage air turbine located in the compressor suction.The turbine is a model of a high-pressure steam turbine component stage on a scale of 1:2.In addition to almost constant air input parameters, this layout also provides easy access to the turbine and to the measuring points.A part of the machine is the direct dynamometer, which determines the speed and the resulting moment.Air, the volume of which is measured by a nozzle,  leaves the compressor pressure discharge and goes out of the laboratory.The turbine is equipped with a traverse device.The traverser enables the probe to move radially (under the blade hub section and above the blade tip), and peripherally (across two stationary blade pitches).It also allows the probe to turn automatically in the flow direction.This enables thorough measurements of the flow field behind stationary and moving blades.There are several static pressure extractors on the turbine -in front of the stage, inside it, and behind it -always on the hub section and tip diameter.There are holes at the input, for inserting e.g. a Prandtl probe, and for measuring the input flow.All pressures are scanned by a fast, 16-channel pressure transducer.Temperatures are scanned by a resistance thermometer in front of and behind the stage.The probe measurement and motion are automatic; the utility program is created in LabView 7.

New blading for the experiment
In 2013, DSPW proposed two variants of a stage designed for testing on the air turbine of the University of West Bohemia, in accordance with newly prepared methodologies, and using new profiles for reaction no./ Measurements in the VT 400 Air Turbine

Evaluation process
Measurements behind the stator and rotor blades were made with the use of a 5-hole pneumatic probe which allows movement around its own axis and also in the radial and circumferential directions.
Calculating the air flow rate.The air flow rate is calculated using the ASME standard bases ṁV = f (p c , ∆p c , T out ).
Calculating the isentropic gradient of the stage.The isentropic gradient of the stage is considered to lie between static pressures Calculating the input and output velocity.
The input and output velocities are axial velocities Calculating the total output state.
Calculating the performance and effective pressure drop.
Calculating the efficiency and the moment of torsion. .
Traversing behind stationary blades.To evaluate the traversing data, we need to know the integral values and we need data from the 5-hole pneumatic probe, after re-calculation according to the calibration (p 1c , p 1s , φ, θ). 5 ≈ •

Traversing behind stationary blades
To evaluate the traversing data, we need to know integral values and data from 5-hole pneumatic probe after re-calculation according to the calibration (p1c, p1s, φ, ϑ).

Traversing behind stationary blades
To evaluate the traversing data, we need to know integral values and data from 5-hole pneumatic probe after re-calculation according to the calibration (p1c, p1s, φ, ϑ).Calculating the gradient and the reaction of stationary blades.

Calculation of stationary blades gradient and reaction
Velocity triangles.
Calculating the efficiency of stationary blades.
Traversing behind moving blades.To evaluate the traversing data, we need to know the integral values, and we need data from the 5-hole pneumatic probe, after re-calculation according to the calibration (p 2c , p 1s , ϕ, θ).
The state in front of moving blades.
Calculating the expansion of moving blades. .
Estimating the velocity c 2 .
Recalculating the expansion.Efficiency of moving blades.

Results of experiments
The variant of the stage with no leanstationary blade was chosen for the initial experiments.All experiments proceeded according to the established methodology.First, integral characteristics depending on the velocity ratio u/c were identified.Individual measurements were executed at a constant speed; and changes in the     By determining an optimal operating regime, we have moved towards another phase, in which flow fields behind stationary as well as moving blades will be measured.
Results of efficiency are presented as relative values.Data from measurements are property of DSPW.
It is apparent from the reaction dependence along the length of the blade that we reach thereaction value around 0.5 in the middle of the blade, which corresponds to our expectations.values of the velocity ratio u/c occurred due to the change in the pressure drop in the turbine.
The measurements were made at several levels of speed (within the range of approx.2000-3000 revolutions per minute), which led to changes in the pressure drop, the Mach number and partly also the Reynolds number.These measurements were used to set the optimal operating state in which further experiments can proceed, particularly measurements by a 5-hole pneumatic probe of the flow fields behind stationary  and moving blades.One of the basic properties of a turbine stage is the dependence of the peripheral efficiency on the velocity ratio u/c.These dependences provide an idea about the optimal operating regime for the stage in order to achieve maximum efficiency.The optimum operating state differs according to the type of blading.The results of the initial experiments are presented in a

Figure 2 .
Figure 2. Forms of blades tested in the "Full3D" stage.

Figure 3 .
Figure 3.View into the laboratory.

Fig. 6 T
Fig. 6 T-s diagram of expansion

Fig. 7 T
Fig. 7 T-s diagram of expansion

Fig. 7 T
Fig. 7 T-s diagram of expansion Figure 7. T -s expansion diagram.

8 Figure 9 .
Figure 9.Comparison of results of particular variants of bladingThis comparison shows a sequential contribution to relative peripheral stage efficiencies.Existing test results show a progressive trend in increasing efficiency, and originally confirm that the newly designed reaction blading represents an appropriately chosen development direction.By determining an optimal operating regime, we have moved towards another phase, in which flow fields behind stationary as well as moving blades will be measured.

Figure 10 .
Figure 10.The reaction course along the relative length of the blade

Figure 9 .
Figure 9.A comparison of the results for different blading variants.

Figure 9 .
Figure 9.Comparison of results of particular variants of bladingThis comparison shows a sequential contribution to relative peripheral stage efficiencies.Existing test results show a progressive trend in increasing efficiency, and originally confirm that the newly designed reaction blading represents an appropriately chosen development direction.By determining an optimal operating regime, we have moved towards another phase, in which flow fields behind stationary as well as moving blades will be measured.

Figure 10 .
Figure 10.The reaction course along the relative length of the blade Figure 10.The course of the reaction along the relative length of the blade.

Fig
Fig. 11The Reynolds number course along the blade

Figure 11 .
Figure 11.The course of the Reynolds number along the blade.