Effects of Honeycomb-Shaped Walls on the Flow Regime Between a Rotating Disk and a Stationary Wall

Abstract

In gas turbines there are many circumstances where coolant flows are introduced between the rotor disk and the stationary housing. This flow serves not only to supply coolant flow to the disk face, but also to restrict the radial inflow of hot gases to be ingested into the clearance from the turbine blade flow field. The amount of the hot radial inflow is influenced by the difference of the disk pumping capacity and the coolant flow supplied near the center. In order to cool the turbine disk with limited supply of coolant air, some means of reducing the radial inflow of hot gases is needed. It is thought that the use of different surface shapes on the stationary housing would inhibit the disk pumping capacity and, therefore, reduce the radial inflow of hot gases into the clearance. To validate the concept, an experimental study was undertaken. The basic geometry investigated was the flow field between a smooth cylindrical rotating disk parallel to a plain circular coaxial wall open to the free space at the disk periphery. Coolant flow is simulated by supplying air through the bore of the stationary wall into the gap. In addition to the base data obtained with the plain stationary wall, a duplicate series of experiments were run with an open honeycomb facing the stationary wall. The effects of the stationary wall surface geometry is assessed by comparing the data with honeycomb facing against the data with plain stationary wall. The flow field is studied through measurements of the static pressure on the stationary wall, radial and tangential velocity measurements in the clearance, the torque on the drive motor, and coolant flow rates. Flows were studied over a gap spacing to disk radii ratio of 0.01 and 0.10, disk Reynolds numbers from 5×105 to 2.2×106 , and throughflow rates from 0 to 3.2 cfs. The results are presented in terms of the tangential and radial velocity profiles in the gap, the static pressure measurements, and the disk torque coefficients. The use of honeycomb on the stationary wall surface grossly altered the ingestion of external flow into the gap from the disk periphery. Important conclusions are: (1) The vacuum in the gap generated by the disk rotation is reduced by a factor of 0.4 to 0.6, depending on the radial location of the point; (2) the core tangential velocity is reduced by a factor of 0.6 to 0.7, depending on the axial spacing and the throughflow number; (3) the critical coolant flow rate is about 63 percent less for the honeycombed surface, as compared to the plain wall case. (4) for a given coolant flow rate, the penetration distance of the radial inflow is much larger for the plain disk than the honeycomb surface.