Anbar Journal for Engineering Sciences

Abstract

Film cooling is one of the methods used to protect the surfaces exposed to hightemperature
flows, such as those exist in gas turbines. It involves the injection of coolant fluid (at
a lower temperature than that of the main flow) to cover the surface to be protected. This
injection is through holes that can have various shapes; simple shapes, such as those with straight
cylindrical or shaped holes (included many holes geometry, like conical holes). The
computational results show that immediately downstream of the hole exit, a horseshoe vortex
structure consisting of a pair of counter-rotating vortices is generated. This vortex generation
affected the distribution of film coolant over the surface being protected. The fluid dynamics of
these vortices are dependent upon the shape of the film cooling hole, and blowing ratio, therefore
the film coolant coverage which determines the film cooling effectiveness distribution and also
has an effect on the heat transfer coefficient distribution. Differences in horseshoe vortex
structures and in resultant effectiveness distributions are shown for cylindrical and conical hole
cases for blowing ratios of 0.5 and 1. The computational film cooling effectiveness values
obtained are compared with the existing experimental results. The conical hole provides greater
centerline film cooling effectiveness immediately at the hole exit, and better lateral film coolant
coverage away of the hole exit. The conical jet hole enhanced the average streamwise adiabatic
film cooling effectiveness by 11.11% and 123.2% at BR= 0.5 and 1.0, respectively, while in the
averaged lateral adiabatic in the spanwise direction, the film cooling effectiveness enhanced by
61.75% and 192.6% at BR= 0.5 and 1.0, respectively