CCS and Power Systems

Advanced Energy Systems - Hydrogen Turbines


Analysis of Gas Turbine Thermal Performance


Performer: Ames National Laboratory

Project No: FWP-AL05205018


Accomplishments


  • Performed CFD simulations that showed that if the Biot numbers of two geometrically similar configurations are nearly the same in magnitude and distribution on both the hot and cold sides of a turbine material, then the magnitude and contours of the normalized temperature and heat flux within the turbine material would be nearly the same. This analogy enables experimental studies of turbine cooling designs at near room temperatures and pressures with greatly scaled-up geometries to allow for more detailed interrogations that provide insight into turbine cooling performance (as if the experiment was conducted under realistic turbine operating conditions with high temperatures, high pressures, and the correct dimensions).
  • Examined three approximations for bulk temperature that are widely used in experimental measurements of the heat transfer coefficient. The work showed that linear interpolation only gives accurate results in straight ducts with an error of less than 3 percent if the flow is turbulent, the two planes where the bulk temperatures are measured are taken in the fully-developed region (i.e., not in the entrance transition region), and the distance between the two planes where linear interpolation is employed is 20 duct hydraulic diameters or less. Other approximations based on the inlet temperature or an averaged bulk temperature give grossly inaccurate results.
  • Performed initial CFD studies to understand how 'pin fins' clearance height-to-diameter ratio and height-to-diameter ratio affect surface heat transfer and stagnation pressure.
  • Performed a study on the flow and heat transfer in the entrance region of a smooth circular duct and the entrance region of a rectangular duct lined with an array of pin fins. During this effort a new nondimensional parameter, called the SCS number was proposed and contrasted with the traditional Nusselt number (Nu). The SCS number has the advantage of not requiring the bulk temperature, which is difficult for the experimentalist to measure. For Nu, the history is embedded in the bulk temperature (Tb). For SCS, the history is built into the SCS number itself. Thus, the magnitude of SCS is also a measure of the "capacity" of the fluid to cool or heat the wall. The SCS may be preferred for quantifying heat-transfer measurements since there will no ambiguity in the Tb used to define heat-transfer. However, when designing heat exchangers, Nu is preferred because Tb is clearly defined. Thus, a formula was developed to convert SCS to Nu and vice versa.
  • Performed a time-accurate conjugate CFD study to understand the unsteady flow and heat transfer in and about a nickel-based super alloy plate heated on one side by a specified heat flux and cooled on the other side by an array of impinging cooling jets with varying heating and cooling loads. Though the cooling supplied ensures that the maximum temperature in the plate is equal to the maximum allowable material temperature when steady state is reached, it was found that the maximum temperature in the plate exceeded the maximum allowable temperature for a substantial amount of time. The duration of over temperature is a strong function of the heat capacity in the material and the variation of the heat-transfer coefficient along the cooled side of the plate.
  • Performed CFD simulations based on steady RANS (Reynolds-averaged Navier-Stokes) closed by the shear-stress transport turbulence model to study the compressible flow and heat transfer in a wedge-shaped duct for the trailing-edge region of a turbine vane/blade under rotating and non-rotating conditions. The objective is to understand the flow mechanisms by which ribs and pin fins in the wedge-shaped duct turn radially outward flow of the coolant from the hub to flow uniformly in the axial direction to cool the entire duct. Results obtained show that pin fins can greatly reduce the size of the separated region when the coolant emerges from the inlet duct to enter the wedge-shaped duct. Also, pin fins provide flow resistance to control the uniformity of the flow along the cross section of wedge-shaped duct in addition to enhancing surface heat transfer via horseshoe vortices about each pin fin. A staggered array of square ribs that extend from the exit of the inlet duct to the tip of the wedge-shaped duct in the  radial direction was found to create two sets of spiraling flows that causes the radial flow exiting from the inlet duct to spiral in the axial direction with one created by the stagnation region upstream of each rib and the other created by the separation downstream of each rib. When there is rotation, the staggered array of ribs was found to mitigate the adverse effects of centrifugal buoyancy by confining flow separation to be between the ribs on the leading face.

Project Details