Handbook of Turbomachinery Second Edition Revised - Ventech!

the turbine static temperature (rotor exit). This approach allows the first
approximate calculation of total pressure, static temperature, and static
pressure in the hot cascade. At this step, there is some error in the three
quantities calculated initially because of the first approximation made of the
specific heat ratio and gas constant. The resulting hot cascade static
temperature, Thc, is much more accurate than the first approximation, which
is Thc ¼ Ttur. If one obtains the necessary properties with the new static
temperature and recalculates the total pressure, static temperature, and
static pressure in the hot cascade, the new result will be more accurate than
the results obtained in the previous steps. If this process is repeated a few
times until the properties converge to a stable value, an exact solution to the
hot cascade total pressure can be obtained.
Once the free-stream total temperature is chosen in the simulating
experiment, the total coolant temperature is calculated by matching the
ratio of total coolant to free-stream temperature of the engine. Although
engine coolant flow rate is usually expressed as a fraction of the main-stream
gas flow rate, different total temperature conditions existing in the turbine
and the simulating experiment may result in significantly different values of
the coolant mass flow rates when the coolant Reynolds number is kept the
same for both the turbine and the simulator (hot cascade rig) due to coolant
viscosity variation. Therefore, the ratio of the hot cascade coolant to freestream
mass flow rate should be adjusted in such a way that it matches the
coolant Reynolds number of the turbine. If the internal cooling passage is
designed with a high coolant velocity, a match of the coolant local Mach
number should be imposed.
Application of actual airfoils (or their prototypes) in the hot cascade
ensures similarity in the conduction heat transfer. Practically useful (for the
final design) conjugate heat-transfer experimental data can be obtained
when external and internal convective heat-transfer similarity is achieved in
addition to similarity in the conduction heat transfer.
Turbine Disc Experimental Boundary Conditions
For the last 30 years there has been a growing interest in fluid mechanics and
heat transfer for the rotating disc systems. Dorfman (1960) [130] published
analytical solutions based on the Reynolds analogy, for the rotating disc–
stator system. Most of the early experimental studies performed for
simplified generic case (unbladed disc rotating in the unshrouded plenum)
were redirected toward practical turbine disc–cooling application. Later
studies have addressed effects of the preswirler, which feeds cooling air into
the blade and disc rim seal to prevent disc plenum from hot gas ingress.
Copyright © 2003 Marcel Dekker, Inc.