An Investigation of Applicability of Transporting Water Mist for Cooling Turbine Vanes
This paper presents a numerical study to investigate the feasibility of transporting mist through the internal cooling channel in high-pressure turbine vanes for film cooling over the vane’s surface. The idea of using mist film cooling to enhance conventional air cooling has been proven to be a feasible technique in the laboratory conditions and by computational simulations. However, there is a challenge to this technique to prove that the water mist can survive in the very hot environment inside the gas turbine casings and internal air passages and be delivered to the film injection holes. Both a zero-dimensional mist evaporation analytical model and 3-D computational fluid dynamic (CFD) scheme are employed for analysis. In the CFD simulation, the Lagrangian /Eulerian method is used along with the discrete phase model (DPM) to track the evaporation process of water droplets. The high-pressure water mist is injected into the stream of cooling air extracted from the compressor through the outer gas turbine casing near the vane before it reaches the vane internal cooling cavity. Using the mist equivalent of 10% of the cooling air mass flow rate, the results show that, when the liquid droplets are atomized to 30 μm in diameter initially, the droplets can survive inside the internal cooling passages and be delivered to the film cooling injection hole location with droplets of 20 μm in diameter; and alternatively, an initially 20 μm droplet can be delivered at 12μm in diameter, which is sufficiently large for completing the required external film cooling task.Copyright © 2012 by ASME
Effects of coolants on the flow and heat transfer characteristics in a non-rotating and rotating two-pass rectangular channel
Abstract The effects of coolants on the flow and heat transfer characteristics in a non-rotating and rotating two-pass rectangular channel with 45-deg angled rib turbulators are numerically investigated using the CFD software ANSYS-CFX. The three-dimensional Reynolds-Averaged Navier–Stokes (RANS) solution with SST turbulence model is applied in this paper. Four kinds of coolants, such as air, steam, mist/air and mist/steam, are used to analyze the effects of coolant types on the heat transfer performance in the channel at six different Reynolds number flow conditions. The channel averaged Nusselt number for air-only are numerically studied and the results are in good agreement with the experimental data. The internal flow pattern and heat transfer characteristics in the channel with air-only are conducted at two kinds of temperature difference. The results indicate that the 39 K temperature difference provides a slightly better heat transfer performance than that of the 60 K temperature difference. In addition, the obtained results show that the mist/steam gives the best heat transfer enhancement and thermal performance in the channel. The detailed flow pattern and Nusselt number distribution for four coolants are also illustrated and discussed.
Unsteady Flow Physics and Performance of a One-and-1∕2-Stage Unshrouded High Work Turbine
This paper presents an experimental study of the flow mechanisms of tip leakage across a blade of an unshrouded turbine rotor. It shows the design of a new one-and-1/2-stage, unshrouded turbine configuration, which has been developed within the Turbomachinery Laboratory of ETH Zurich. This test case is a model of a high work (Δh/u 2 = 2.36) axial turbine. The experimental investigation comprises data from unsteady and steady probe measurements, which has been acquired around all the bladerows of the one-and-1/2-stage, unshrouded turbine. A newly developed 2-sensor Fast Response Aerodynamic Probe (FRAP) technique has been used in the current measurement campaign. The paper contains a detailed analysis of the unsteady interaction between rotor and stator blade rows, with particular attention paid on the flow in the blade tip region. It has been found that the interaction of the rotor and the downstream stator has an influence on the development of the tip leakage vortex of the rotor. The vortex is modulated by the stator profiles and shows variation in size and relative position to the rotor trailing edge when it stretches around the stator leading edge. Thereby a deflection of the tip leakage vortex has been observed, which expresses in a varying circumferential distance between two neighboring vortices of ±20% of a rotor pitch. Furthermore, a significant influence of quasi-stationary secondary flow features of the upstream stator row on the secondary flow of the rotor has been detected. The geometry and flow field data of the one-and-1/2-stage turbine will be available to the turbomachinery community for validation and improvement of numerical tools.