Fundamental and Experimental Aerodynamics
Turbine Test Bench VEGA2
Rodor blade row at VEGA2
At the beginning of the nineties, no experimental set up dedicated to turbines were available in France.
Industrial partners, university and ONERA decided to build a new turbine test bench. The new research
facility (Turma) should allow the study of the HP-LP interaction with the counter-rotating turbines in which
engine shafts turn in opposite directions. This new set up should also allow the study of blade cooling. Since the
realization of such a project is long and difficult, it was decided to define an intermediate first step that consists of
building a more modest set up to study the aerodynamic interactions in transonic HP turbine. This facility, called
VEGA 2, has been built to validate the three dimensional Navier-Stokes unsteady codes and to adapt the non-intrusive
experimental techniques developed at ONERA for turbomachinery applications: particle image velocity (PIV),
laser induce fluorescence (LIF), Raman diffusion, Doppler global velocimeter (DGV)...
The VEGA 2 Experimental facility
This test bench has been designed in co-operation with three industrial partners: Snecma, Turbomeca and
Edf. It has been installed at the Chalais-Meudon center. It is a derivative circuit of the transonic S5Ch wind
tunnel. The wind tunnel compressor furnishes the driving air and a heat exchanger permits to adjust the inlet total
temperature.
VEGA2 test bench in S5Ch
Installation Drawing
It can be observed that both hub
and tip have been chosen cylindrical to reduce the three-dimensional effects and also to facilitate the
measurements. The rotor is installed overhanging in a first bearing. The torque is transmitted by means of the
two coupling shafts through a second bearing installed in the inlet. The hydraulic brake is used as a means of
absorbing the power and of controlling the speed. There are no torque measurements. Mainstream mass flow rate
is measured through an upstream venturi flow meter.
The turbine has the following mean characteristics:
- Mass flow: 3 kg/s
- Work capacity: 265 J/kg.K
- Nominal speed: 13000 rpm
- N /
Tio: 650
- Flow coefficient: 77.2 (kg/s). K /bar
- Aerodynamic loading Dh/U2 =1.20
- Rotor hub/tip ratio 0.775
- Hub radius 0.190 m
- Number of blades
- Inlet total pressure 0.8 bar
- Inlet total temperature 400 K
- Nominal power 318 kW
Instrumentation
Meridian Plan
The above figure shows the meridian channel. Upstream of the cylindrical part, a convergent section accelerates
the flow to reduce the heterogeneous disturbances due to the alimentation circuit. Upstream of the stator seven azimuthal locations can be used to explore the inlet flow, in particular by means of boundary layer probes. In this
annular section, the hub and the casing are equipped with static taps. Three stator blades are equipped with 165
static taps on the suction and pressure sides. These taps are evenly distributed on 5 sections along the profile
blades. One blade is equipped with 12 high frequency response pressure transducers on the suction surface
between the throat and the trailing edge.
Nine blades of the rotor are equipped with 30 unsteady transducers, on the suction and pressure sides and a pitot
probe at the leading edge. Three sections at 10%, 50% and 90% are instrumented. The figure below presents three
instrumented blades of the rotor. The technique used for the equipment has been developed by OXFORD
University and the Kulite company. The transducer wiring passes through this shaft which is tubular and are
connected to a slip ring. To study the unsteady effects due to the stator wake the axial gap can be varied between
1/4 to one axial chord.
VEGA2's intrumented blades
A radial and a tangential traverse plane located approximately one axial blade chord downstream can be
probed by means of a five-hole probe. These measurements allow the determination of the outlet flow field of
the stage. Exit total pressure and temperature measurements are also done using six rakes located four blade
chords downstream. Three rakes are made with six pitot probes each and three other with six ventilated
thermocouple probes. Farther downstream the work capacity is controlled by means of two thermocouples
placed in the plenum.
This set up is also adapted for non-intrusive optical diagnostics. The figure below shows in which way the
problem has been solved. On the casing we can see the squared tubes through which the laser planes can be
introduce in the stator or in the rotor. The inter stage area can be reached by means of two tubes placed face to
face. Thus it is possible to introduce laser planes or beams everywhere in the stage. Two traps can be used for the
installation of CCD camera or other optical devices.
VEGA2's intrumented casing
Experimental investigations
One first campaign devoted to stationary measurements has been carried out. Measurements for
different work capacities (+15% to -40%) and different rotational speed (+8% to -30%) have been performed.
Comparison between steady 3D viscous flow computations and experimental investigations
The test results can be compared with predictions from a viscous three-dimensional Navier-Stokes solver. In
particular, a comparison has been made for the nominal design point. The computations were performed by
ONERA’s CANARI code. The averaged Navier-Stokes compressible equations are solved in the relative frame
and cartesian coordinates. The turbulence model is either a two-equation model (Jones-Launder) or an algebraic
model (Baldwin-Lomax or Michel).
Simulation with CANARI Code
Future planes
We have planned many projects for the second semester. Non intrusive temperature measurement using
spontaneous rotational Raman spectroscopy will be performed by the end of the year. This laser technique will
be used to measure the static temperature downstream of the stage. The results are obtained from Raman
scattering of air by using a high repetition rate pulsed Nd: YAG laser and a spectrally and spatially resolving
detector system that consists of a triple spectrograph and a CCD camera. It is a diagnostic tool that has the
capability of providing quantitative measurements of static temperature with good accuracy. This optical technique (i.d. scattering shifting technique) is well suited for the severe experimental constraints usually
encountered in turbomachinery rigs [2].
A PIV campaign is also planned this
year.
