Coupled Effect of Expansion Ratio and Blade Loading on the Aerodynamics of a High-Pressure Gas Turbine

Abstract

Abstract:The need of a continuous improvement in gas turbine efficiency for propulsion and power generation, as well as the more demanding operating conditions and power control required to these machines, still ask for great efforts in the design and analysis of the high pressure section of the turbo-expander. To get detailed insights and improve the comprehension of the flow physics, a wide experimental campaign has been performed in the last ten years at Politecnico di Milano on the unsteady aerodynamics of a high-pressure turbine stage considering several operating conditions. This paper presents and discusses the experimental results obtained for the stage operating with different expansion ratios and rotor loading. The turbine stage under study is representative of a modern high-pressure turbine and can be operated in both subsonic and transonic conditions. The experimental tools applied for the current research represents the state of the art when unsteady investigations are foreseen. The detailed flow field, the blade-rows interaction and the overall performance are described and discussed; efforts have been devoted to the discussion of the various contribution to the overall stage efficiency. The direct effects of the expansion ratio, affecting the Reynolds and the Mach numbers, have been highlighted and quantified; similarly, the indirect effects, accounting for a change in the rotor loading, have been commented and quantified as well, thanks to a dedicated set of experiments where different rotor loadings at the same expansion ratio have been prescribed.

Design and Commissioning of a Combustor Simulator Combining Swirl and Entropy Wave Generation

“…In this section, the combustor simulator, the wind tunnel and the measurement techniques are described. A description of the turbine test facility is proposed in [17]. Here, the results are discussed for an operating condition, called OP3 in [17], that exploits a stage expansion ratio of 1.4 with a flow Mach number approaching the stator of 0.14.…”

Hot Streak Evolution in an Axial HP Turbine Stage

“…In fact, given a total pressure loss coefficient of about 5.9% for the reference condition [14], the increase on the single stator channel (ΔY%) due to the hot streak injection is within 0.2% to 0.6%, as reported in Table 3, i.e., one order of magnitude lower and, for some cases, within the measurement uncertainty. The total temperature increase (ΔTt) is slightly changing with the minimum for the leading edge case, where the hot streak interacts directly with the blade and, for this, an effect of the heat exchange with the blade wall is expected, even though very difficult to quantify.…”

“…The impact of the hot streak on the blade wake can be observed in Figure 5, which reports the total pressure loss coefficient distributions for the reference and the hot streak conditions, as well as their difference; the wake retains its general width and deficit, even though a small tangential shift is found especially above the midspan. The stator-exit vorticity field, not reported for sake of brevity, does not show a specific effect of the hot streak on the stator secondary flow for LE injection (the reader is referred to [14] for a comprehensive discussion of the stator aerodynamics in the absence of hot streak injection). Overall, the hot streak injection slightly changes the cascade loss coefficient, especially above the midspan (namely, where the jet impinges on the blade), as reported in Figure 6.…”

“…Table 1 provides relevant information on the turbine geometry, as well as the reference operating conditions of the present tests. For this first study on hot-streak migration in the turbine, subsonic conditions were considered (even though measurements in transonic conditions have been recently published in [14]). The aerodynamics of the turbine operated in subsonic conditions was extensively studied in the last decade and can be found in [15][16][17].…”

Stator-Rotor Interaction in Axial Turbine: Flow Physics and Design Perspective

“…In fact, when the rotor loading increases, the rotor suction side boundary layer is more prone to instability and the rotor vortical structure more intense, making all of them more sensitive to any variation coming from upstream. Figure 11, shows the relative total pressure coefficient and deviation angle standard deviations, calculated among the different time instants, for a negative incidence conditions (Figure 11a, incidence at midspan = −10°) and a positive one (Figure 11b, incidence at midspan = +10°) [35].…”