Spanwise Transport of Total Enthalpy through a Turbine Nozzle

Flow exiting the combustor a gas turbine engine is highly turbulent and contains significant spatial gradients of pressure and temperature. The high pressure turbine vanes operating in this environment redistribute these spatial gradients and impact the inflow characteristics of the turbine rotor blades. The efficacy of the turbine design is predicated on the knowledge of this redistribution process.

This work seeks to understand the physical mechanisms that transport total enthalpy normal to a line of constant span in a turbine nozzle vane. This goal is accomplished through a combination of experiment and computational work. Detailed experimental surveys of total temperature and total pressure were obtained upstream and downstream of an annular turbine nozzle vane cascade. The facility used was capable of replicating engine relevant conditions including high inflow turbulence intensity, inflow non-uniformities in total pressure and total temperature, and vane exit Mach numbers. Three sets of inlet boundary conditions were studied. The first set had a nominally uniform distribution of total temperature. The second and third set had variation of total temperature in the spanwise direction. All three sets of inlet boundary conditions had nominally the same inlet total pressure profile and inlet Mach number.

Numerical simulations were performed using the commercial software ANSYS Fluent. The experimental data obtained upstream of the vane was used to define the numerical inlet boundary conditions. The static pressure distribution on the surface of the vane was matched by setting the downstream static pressure. Closure was obtained by using the k-\omega SST turbulence model. Transition was modeled using a single equation involving the intermittency. The simulation was validated using the experimental data obtained downstream of the vane. The data obtained from the simulation was used to study the mechanisms which transport the total enthalpy normal to a line of constant span. Two mechanisms were identified that accounted for the majority of the redistribution of total enthalpy. The first was the turbulent heat flux normal to a line of constant span and the second was the mean convective transport of total enthalpy normal to the line of constant span.