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
Simulation of Mist Film Cooling on Rotating Gas Turbine Blades
Film cooling technique has been successfully applied to gas turbine blades to prevent it from the hot flue gas. However, a continuous demand of increasing the turbine inlet temperature to raise the efficiency of the turbine requires continuous improvement in film cooling effectiveness. The concept of injecting mist (tiny water droplets) into the cooling fluid has been proven under laboratory conditions to significantly augment adiabatic cooling effectiveness 50–800% in convective heat transfer and impingement cooling. The similar concept of ejecting mist into air film cooling has not been proven in the laboratory, but computational simulation has been performed on stationary turbine blades. As a continuation of previous research, this paper extends the mist film cooling scheme to the rotating turbine blade. For the convenience of understanding the effect of rotation, the simulation is first conducted with a single pair of cooling hole located near the leading edge at either side of the blade. Then a row of multiple-hole film cooling jets are simulated at stationary and rotational condition. Operating condition under both the laboratory (baseline) and elevated gas turbine conditions are simulated and compared. The effects of various parameters including mist concentration, water droplet diameter, droplet wall boundary condition, blowing ratio, and rotational speed are investigated. The results showed the effect of rotation on droplets at lab condition is minimal. The CFD model employed the Discrete Phase Model (DPM) including both wall film and droplet reflect conditions. The results showed that the droplet-wall interaction is stronger on the pressure side than on the suction side resulting in a higher mist cooling enhancement on the pressure side. The average mist cooling enhancement of about 15% and 35% are achieved on the laboratory and elevated conditions, respectively. This translates into a significant blade surface temperature reduction of 100–125 K with 10% mist injection at elevated condition.Copyright © 2009 by ASME
Observations on the Influence of Rotation on Heat Transfer in the Coolant Channels of Gas Turbine Rotor Blades
This paper reports the results of an experimental study of the combined influence of Coriolis acceleration and centripetal buoyancy on heat transfer in a cylindrical tube which rotates about an axis orthogonal to its axis of symmetry. It is demonstrated that for a radially outward flow, Coriolis acceleration tends to improve heat transfer. However the Coriolis-induced improvement to heat transfer may be nullified and reversed due to centripetal buoyancy and this is demonstrated. Proposals are made which permit an overall assessment of these two interacting effects to be made. The implications of the results reported in relation to the design of conventionally cooled turbine rotor blades are discussed.