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Handbook of Turbomachinery Second Edition Revised - Ventech!

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(streamwise), the Z-coordinate along the blade-to-blade direction, and the zcoordinate<br />

positioned along the spanwise direction. Viscous terms in the<br />

streamwise direction are neglected and turbulence effects are modeled using<br />

the Baldwin–Lomax turbulence model. The resulting time-dependent<br />

governing equations are as follows:<br />

Where<br />

" ! #<br />

qq<br />

qt þ J q ^E<br />

qx þ q ^F<br />

qZ þ q ^G<br />

qz Re 1 q ^Fv<br />

qZ þ q ^Gv<br />

qz<br />

t is time.<br />

q is the vector <strong>of</strong> conserved flow variables.<br />

^E; ^F; ^G are the inviscid flux terms.<br />

^Fv; ^Gv are the viscous flux terms.<br />

^H is a source term due to blade rotation.<br />

J is the Jacobian <strong>of</strong> coordinate transformation.<br />

¼ ^H ð5Þ<br />

The equations are nondimensionalized using appropriate reference quantities,<br />

and the Reynolds number (Re) and Prandtl number (Pr) are defined in<br />

terms <strong>of</strong> these quantities. The specific heats, Cp and Cv, and Prandtl number<br />

are assumed to be constant. A multistage Runge–Kutta scheme is used to<br />

solve the discretized form <strong>of</strong> the equations.<br />

Boundary Conditions<br />

The total temperature and total pressure are specified upstream <strong>of</strong> the<br />

turbine blade (inlet). For supersonic inflow, all flow variables are specified at<br />

the inlet. For subsonic outflow, the exit static pressure is specified and the<br />

conserved flow variables are derived using extrapolation. On the blade<br />

surface the normal velocity component is set to be zero. For viscous flows,<br />

the velocity (all components) is set to be zero at the blade surface. At the<br />

film-cooling holes, the boundary conditions <strong>of</strong> the flow solver are modified<br />

to account for the mass flow rate, temperature, and pressure <strong>of</strong> the filmcooling<br />

air entering the external flow field.<br />

Internal Cooling<br />

The internal coolant flow in a gas turbine blade is complex and threedimensional.<br />

The complexity <strong>of</strong> the computations is increased further due to<br />

factors such as thermal buoyancy, Coriolis effects on the internal flow, etc.<br />

As a result, the computational effort and resources needed for a detailed<br />

evaluation <strong>of</strong> the coolant flow are prohibitive in an optimization procedure<br />

Copyright © 2003 Marcel Dekker, Inc.

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