This paper presents the results of a numerical investigation of the gap influence on the turbine efficiency. The rotor-stator interaction in a (1/2)-stage turbine is simulated by solving the quasi-three-dimensional unsteady Euler/Navier-Stokes equations using a parallelized numerical algorithm. The reduced turnaround time and cost/MFLOP of the parallel code was crucial to complete the numerous run cases presented in this paper. The inter-row gap effect is evaluated for 4 gaps, 3 radial positions and 3 angular velocities. As expected, the results presented in this paper show that the efficiency increases and losses decrease while the gap size increases. The maximum efficiency location, however, corresponds to values of the gap size which may be too large for practical use (approximately inch). Fortunately, a local maximum efficiency and minimum losses location has been found at approximately 0.5 inches gap size. The efficiency variation near the local optimum is large, in some configurations being as high as 1.4 points for a gap size variation of only 0.076 inches. Data produced by the numerical simulations can be used to develop a design rule based on the inter-row gap size.
The industry issues of minimizing maintenance and maintaining turbine performance with operating time have been systematically addressed using creative approaches to control wear, erosion, vibration, and distortion of critical High-Pressure (HP) and Intermediate-Pressure (IP) Steam Turbine components. The important components were identified utilizing a new technique to analyze turbine high maintenance areas. New technology advances were utilized to understand the causes of the maintenance, and to reduce or eliminate it. The technology advances discussed in the paper are in the area of three-dimensional computer programs, materials, coatings, modern computer-aided drafting, and verification testing. These, in conjunction with new creative design approaches for the critical components, have resulted in a ruggedized HP and HP/IP turbine design, which is retrofittable in today’s operating units. Of special interest are the steps taken to give rapid and individually customized attention from design through manufacturing to each unique situation and utility. Among the benefits achieved are up to a 50 percent overall reduction in maintenance, up to 120 Btu/kWh (30 kcal/kWh) reduction in heat rate, and an increased cyclic duty capability for the ruggedized turbines.
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