Convegni ATI - Accesso riservato soci CTI

Autore: L. Battisti, T. Arts

Collana: CA - 51 - Udine 1996

Note:
The thermodynamic efficiency of a gas turbine cycle can be improved by increasing the combustion chamber exit temperature. This increase is mainly limited by the thermal characteristics of the first stage vane and blade material; nowadays, cooling and/or surface protection systems have systematically to be considered. Conventional, powerful cooling systems range from internal forced convection, through impingement, to film, transpiration and effusion. Internal forced convection is realized by introducing “cold” air, through the root section, into internal cooling channels and blowing it out through the tip and/or trailing edge sections. The heat exchange takes place between the walls of these internal serpentine passages and the coolant flow. In order to maximize the heat transfer levels, turbulence promoters are periodically located onto one or two opposite walls.
The flow in internal cooling passages can experimentally be modeled as a flow developing in a series of straight and curved ducts. In order to quantify the thermal field, the wall temperature distributions of these test sections are measured by means of different techniques such as liquid crystal or infrared thermography and thin films. As opposed to the thin film technique, the liquid crystal or infrared thermographies allow a non-discrete, non intrusive temperature measurement; they nevertheless require a quite heavy processing of the acquired images. Equilibrium flow as well as short duration facilities can be selected to perform these investigations.
Wall heat flux measurements in a rectilinear channel by means of a transient technique are discussed in the present contribution. The heat transfer coefficient distribution, corresponding to a uniform temperature boundary condition, is then deduced. A comparison with the results obtained by means of liquid crystal thermography is finally performed.