Experimental investigation of moment coefficients in open rotor-stator disc systems

Abstract

This study presents experimental investigations of moment coefficients in an open rotor-stator disc system by use of a novel thermoelectric sensor with a measurement area of approximately 1.2 mm². A test rig has been built that has the capability of reaching rotational Reynolds numbers representative for instance of a modern gas turbine. Measurements were carried out with a 0.5 m diameter rotor disc rotating up to 8500 rpm with a gap ratio between 0.008 and 0.04 and a stator disc of the same diameter. The utilized sensor setup enables measurements at high centrifugal acceleration up to 25500 g, which have already been tested in previous studies. The measuring method based on the over temperature or rise-temperature and adjustment method, which is applied locally. A thermal model is used to determine the thermal resistances and heat capacities of the substrate by measuring the over temperature and the electrically supplied heating power. The heat transfer coefficient at the heating area can also be determined via this model. The sensor calibration is done in a rectangular channel with fully developed flow and different over-temperature values. These determined heat transfer coefficients can be transferred via a calibration relationship into wall shear stresses. Subsequently, the validations are performed on a flat plate in a wind tunnel with a well-known flow situation. The results are in very good agreement with known correlation out of the literature. Furthermore, radially wall shear stress distributions are measured on stator disc by using the calibrated sensors. Moment coefficients and averaged Nusselt numbers have been calculated from these measurements in the range between Reφ = 2.55·105 and 3.48·106. The obtained results are compared with known references for rotor stator systems. The moment coefficient on stator are considerably lower compared to the rotor disc. The averaged Nusselt numbers show a good agreement for the lowest investigated gap ratio on stator disc compared to literature data for enclosed rotor stator systems.