24I18 IJAET0118698 v6 iss6 2524 2530.pdf
International Journal of Advances in Engineering & Technology, Jan. 2014.
EFFECT OF COOLING AIR TEMPERATURE ON COOLING
EFFECTIVENESS OF HIGH PRESSURE TURBINE NOZZLE
Venkatasubramnaya S1, Vasudev S A1 and Sunil Chandel2
Turbine Research Establishment, Bengaluru, India
2Department of Mechanical Engineering,
Defence Institute of Advanced studies Girinagar, Pune, India
High pressure turbine nozzle guide vane of a gas turbine engine, which operates at gas temperatures in excess
of 1700 K, employs various cooling techniques to keep the vane within safe operating limits. Even though nozzle
guide vanes are designed using heat transfer co-relations available in published papers and fundamental data,
it is required to test the nozzle guide vane to ascertain the surface metal temperature and verify the adequacy of
cooling. Adequacy of cooling is quantified by the term cooling effectiveness expressed and as percentage.
Cooling effectiveness is a function of gas temperature, cooling air temperature and surface metal temperature.
The objective of the current work was to study the effect of cooling air temperature on cooling effectiveness.
Tests were conducted on a high pressure turbine nozzle guide vane. Gas pressure, gas temperature, cooling air
pressure was kept constant and the cooling air temperature was varied as a ratio of gas temperature to cooling
air temperature and its effect on metal temperature studied. It was seen that, over the range of cooling air
temperature tested, cooling effectiveness remained sensibly constant. Such tests also assist in estimating the
surface metal temperature of the nozzle guide vane in the engine.
KEYWORDS: Cooling effectiveness, nozzle guide vane, cooling air temperature
Nozzle guide vanes of high pressure turbines in modern gas turbine engines operate at gas
temperatures in excess of 1700K and employ internal cooling, augmented convective cooling like pin
fins and post box ejection, impingement cooling and film cooling to keep the vane surface
temperature within safe limits.
Even though the design of the cooling configuration is often based on measured heat transfer coefficients and other fundamental data, for a particular geometry it is required to ascertain the metal
temperature attained by the nozzle guide vane and verify its adequacy of cooling. The creep life of
vane can get reduced drastically for a further 15K increase in metal temperature if the vane is already
operating close to its allowable temperature limit. It is best to evaluate the adequacy of the cooling
configuration by rig tests. Scaled rig tests [1,2] may be conducted at reduced conditions of gas
temperature and pressure and their results may be directly compared to that of the engine provided
the results are compared on the basis of cooling effectiveness defined as
Where Tg is gas temperature, Tc is cooling air temperature and Tm is surface metal temperature and η
is the cooling effectiveness and generally expressed in percentage. η can vary from 0 to 1 meaning
that if η = 0 then metal temperature Tm will be equal to gas temperature Tg and if η = 1 then metal
temperature Tm will be equal to cooling air temperature Tc.
Vol. 6, Issue 6, pp. 2524-2530