Latest revision as of 18:45, 11 February 2017

Steam turbine rotor cascade

Application Challenge 6-12 © copyright ERCOFTAC 2004

Test Data

Overview of Tests

Experiments were carried out in the wind tunnel in the High-Speed Laboratory of the Institute of Thermomechanics AS CR in Prague. The blown-down wind tunnel connected to the vacuum storage (6500 m³) has a turnable test section that is 160 mm in width and 220 – 600 mm in height depending on the cascade stagger. The maximum error of inlet angle setting is 0.1 deg. The experimental facility provides the possibility of pneumatic and optical measurements in the range of Mach numbers up to M ≈ 2. The tunnel is equipped with a Mach-Zehnder interferometer (mirror Ø 156 mm) and schlieren optics, both can be used either with a nanosecond spark source or a Video system. A semi-automatic traversing device together with a digital measuring system is used to measure cascade losses as well as other aerodynamic data. The tunnel is especially suited for turbine cascades which can be measured within the range of exit Mach numbers (0.5; 2) and inlet angles β₁ (30 deg; 150 deg).

The SE 1050 blade cascade was designed for the inlet flow angle β₁ = 70.7 deg, the isentropic exit Mach number M_2is = 1.208 and for wet steam. The flow in the blade cascade was investigated within a wide range of exit Mach numbers and inlet angles by the Mach-Zehnder interferometer.

Test data are based on interferometric pictures taken for various flow conditions. The density difference between two adjacent fringes is given by the wave length of monochromatic light and the wind tunnel width by the relation Δρ = 0.011858 kg/m³. Detailed description of the evaluation procedure is given by Šafařík (1996). The basic series was made for the inlet angle β₁ = 70.7 deg (incidence i = 0 deg) with the exit isentropic Mach numbers changed in the range (0.489, 1.387). Measurements were carried out for following values of Mach numbers:

M₁	M_2is	M₁	M_2is
0.279	0.489	0.376	1.007
0.322	0.610	0.376	1.099
0.354	0.716	0.375	1.198
0.364	0.793	0.379	1.313
0.365	0.906	0.377	1.387

The case corresponding to nearly design conditions with M_2is=1.198 was chosen for the Application Challenge.

The measurement covers the values from low subsonic to supersonic exit velocities including the transonic region. Additional experiments were carried out for extreme values of incidence i = 70.7 -β₁ covering the range from i = -67 deg (very small loading) to i = +30 deg (overloading conditions).

i (deg)	M₁	M_2is
-67	0.545	0.905
+30	0.660	1.012

The pressure distribution on the profile surface was evaluated from interferometric pictures. Besides interferograms, measurements downstream of the cascade were carried out for various incidence i and the Mach number M_2is giving exit flow angle β₂ and the energy loss coefficient ζ. Measurements of exit angle and energy losses were made in the distance one chord behind the cascade. The coefficient ζ is given by the relation

where λ₂ is the relative velocity.

Test Case EXP-1

Description of Experiment

The flow regime near the design conditions (the inlet angle β₁ = 70.7 deg and the isentropic exit Mach number M_2is = 1.198) was accepted to be the test case EXP1. The relevant parameters are given in the Table EXP-A.

Boundary Data

Inlet conditions are characterized by the total pressure and the total temperature upstream the cascade. The flow regime was adjusted by means of the back pressure in the settling chamber downstream the cascade. The back pressure was controlled by the throttling valve.

The profiles of the blade cascade were manufactured in high precision. The surface was smooth (glossy steel).

Measurement Errors

The dependence of Mach number errors on the value of the inlet Mach number was derived for interferometric measurements. The Mach number error can be estimated as δM = 0.005 for the Mach number M ≈ 1.

The errors of pressure and temperature were δP = 70 Pa and δT = 0.1 K. The error analysis of the data reduction method for the evaluation of the exit angle and the kinetic energy loss coefficient has not been carried out. The maximum error of the exit angle was estimated to be about 0.3 deg.

Measured Data

EXP1 Measurement of flow in the steam turbine rotor cascade: interferogram of the flow field, pressure distribution on the blade, survey of relevant parameters (given in the file exp12.dat)

The files containing results with measured and evaluated parameters are given in Table EXP-B:

exp11.jpg (interferogram with density isolines for M_2is = 1.198)

exp12.dat (survey of relevant parameters β₁, i, M₁, M_2is, Re_2is, ζ, β₂, p₀₁, T₀₁, pressure distribution on the suction and pressure sides p/p0 vers. x/b)

Table EXP-A Summary description of all test cases
Name	GNDPs		PDPs (problem definition parameters)			MPs (measured parameters)
	Re	M_2is	inlet angle β₁ (deg)	total pressure p_o1 (Pa)	total temperature T_o1 (K)	detailed data ρ (kg/m³)	[../../help/glossary.htm DOAP]s
EXP 1	1.48 x 10⁶	1.198	70.7	98071.7	298.65	ρ=f(x,y)	p/p_o=f(x/b), ζ, β₂

Table EXP-B Summary description of all measured parameters and available datafiles
	MP1 interferogram density isolines	MP 2 pressure distribution p/p_o (1)
EXP 1	exp11.jpg	exp12.dat

References

[1] Šafařík P. Experimental data from optical measurement tests on a transonic turbine blade cascade, Proc. of the 13^th Symposium on Measuring Techniques for Transonic and Supersonic Flow in Cascades and Turbomachines (eds. C. Grossweiler, G. Gyarmathy), 20/0-20/14, ETH Zürich, 1996

[2] Šťastný M., Šafařík P. Experimental analysis data on the transonic flow past a plane turbine cascade, ASME Paper 90-GT-313, 1990

[3] Šťastný M., Šafařík P. Boundary layer effects on the transonic flow in a straight turbine cascade, ASME Paper 92-GT-155, 1992

Contributors: Jaromir Prihoda; Karel Kozel - Czech Academy of Sciences