Cooling of Gas turbine buckets to ensure adequate life margin with coolants at advanced engine conditions of pressure and temperature requires that the internal heat transfer as influenced by rotation be known with sufficient accuracy. The existing data base, comprised of information readily available in the open literature has limited advanced design applicability considering the range of geometric and fluid-thermal dimensionless parameters of interest. Further, studies conducted with the aid of computational fluid dynamics (CFD) have demonstrated that, as the range of such parameters is extended, the characteristics of the predicted heat transfer capability change significantly, to the extent that bucket coolant passage designs that are fully acceptable at state-of-the-art conditions are marginal or unacceptable at advanced conditions. The purpose of this paper is threefold, to: a) demonstrate the need for extending the current internal heat transfer data base, accounting for the effects of rotation, b) provide a physical understanding of the expected heat transfer characteristics at advanced conditions, and c) describe a test rig and test program focused on obtaining the data of interest.

Three-dimensional laminar flow over a flat plate with uniform suction is considered for a specific class of outer-flows. A series solution of the boundary-layer equations is obtained for the asymptotic ease, that corresponding to transverse velocity which is everywhere constant. The limitations of the asymptotic solution are examined in terms of existing theory and experimental data for the analogous two-dimensional ease. A numerical example, typical of aircraft flight parameters, is discussed in relation to the analogous impermeable wall ease.

The role of particulate contaminants in advanced gas turbine coolants is discussed, especially in light of the extremely high G-field regions they will experience in service. Predictions of sedimentation in both laminar and highly turbulent accelerating flows using a computational fluid dynamics code are made for a range of particulate sizes to show that particles over 0.5 µm are of concern. Possible techniques for limiting access of these particulates to the gas turbines themselves are presented. Overall, contaminant deposition appears controllable, limiting required cleaning of coolant channels to regularly scheduled inspections.

No abstract

Wet steam is a common occurrence at the exhaust of the LP turbines in fossil-fired steam plants. In nuclear turbines, wet steam will be found right from the high-pressure sections. The presence of moisture in steam reduces the aerodynamic efficiency of the turbine sections, thus reducing the overall efficiency of the turbine. Additionally, water droplets also cause erosion and corrosion of buckets and other components. LP turbines account for a significant portion of the total cost of the turbines (due to the enormous sizes required by the expanding steam) and produce significant portion of the power output. Measuring and controlling wetness will help improve both the performance and reliability of turbines. A novel way of measuring the composition of wet steam using a speed of sound based technique is being developed. The technique, based on technology developed for measuring two-phase flow compositions in down-hole (oil-field) applications, relies on measuring acoustic pressures propagating in a one-dimensional wave-guide (pipe or tube) using an array of axially located pressure transducers. The technique is non-intrusive to the flow field and relies on passive listening of the noise generated by the flow itself (and, hence differs from the conventional ultrasound based techniques). The current study is an ongoing effort and the paper will focus on the feasibility of this technique for wet steam application. The eventual aim is to be able to measure steam wetness in the range of 0–10% with an accuracy of ± 0.2%. Initially, the ability of the technique to accurately measure the wetness in air-water mixture was established using an air and water mist facility. Next, high subsonic flow conditions were evaluated in single phase (air only) flow using a wind tunnel facility. Excellent agreement between speed of sound calculated for air, based on conventional pressure and temperature measurements in a wind tunnel, and that measured directly by the probe was obtained. The wind tunnel tests showed that the SOS measured by the probe and conventional instrumentation agreed within ± 1.5%. This establishes that the technique is capable of accurately measuring the speed of sound, which is the primary variable to calculate the flow composition. The technique can also be used to measure volume. Although the wind tunnel tests were not specifically designed to assess the accuracy of the flow rate measurement, comparisons were made between the flow velocities given by the probe and reference measurements. The additional motivation was to assess the ability of the probe to monitor volume flow/mass flow at high Mach numbers where only shorter straight sections are available. The flow velocities measured by the probe agreed with those calculated using the wind tunnel instrumentation (wall-static taps) within the estimated uncertainty levels introduced by the flow blockage and profile distortions. Additional tests are planned to assess flow rate accuracy. Effort is continuing to study steam flows representative of exhaust of low pressure steam turbines in steam plants.