Axial-flow turbines turbine losses

The primary cause of efficiency losses in an axial-flow turbine is the buildup of boundary layer on the blade and end walls. The losses associated with a boundary layer are viscous losses, mixing losses, and trailing edge losses. To calculate these losses, the growth of the boundary layer on a blade must be known so that the displacement thickness and momentum thickness can be computed. A typical distribution of the displacement and momentum thickness is shown in Figure 9-26. The profile loss from this type of bound-ary-layer build-up is due to a loss of stagnation pressure, which in turn is... 

Brown, L.E., Axial Flow Compressor and Turbine Loss Coefficients A Comparison of Several Parameters, Journal of Engineering for Power, ASME Transactions 94A, pp. 193-201, 1972. 

The power consumption of an impeller is the product of the pumping capacity (circulation fiow rate) and the velocity head, which is directly related to shear rate and turbulence. Depending on the type and size of the impeller, either the flow or the turbulence can be favored [110]. Axial flow impellers usually produce a fluid motion that is downward at the central axis of the vessel and upward in the wall region. They are designed to produce a high flow/power ratio with little turbulent loss. The designs of axial-flow impellers are derived from three-blade propellers. Radial-flow turbines produce a radial fluid motion from the impeller to the wall, where the radial flow separates into an upper and a lower circulation loop. They are characterized by a relatively low flow/power ratio, with much of the energy dissipated by turbulence around the impeller. Radial-flow turbines have flat blades or a disk with flat blades. 

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