اثر کلاکینگ ردیف پره بر عملکرد پایا و ناپایای آیرودینامیکی توربین کم فشار موتور توربین گاز
The aerodynamic efficiency of a gas turbine engine is particularly influenced by the performance of its low-pressure unit. An increase of 1% in the polytropic efficiency of the low-pressure turbine (LPT) can reduce fuel consumption by approximately 0.5% to 1%. For a gas turbine engine, consider an initial aerodynamic design that satisfies all performance requirements and allowable parameter limits, while the final blade profile configuration is obtained through an optimization process. According to reputable references, optimizing high-efficiency gas turbine engines with aerodynamic efficiencies exceeding 90% is a challenging task. Under such conditions, and in response to the demand for improving the cycle efficiency of these turbomachines, blade-row clocking techniques can be employed. Clocking enables the circumferential alignment of one or more blade rows relative to a reference coordinate system or a reference blade row, allowing the controlled entrance of upstream wake flow to downstream stage(s)
Considering the aerodynamic effects of rotor–stator interaction and wake–blade interaction, low-pressure turbines are increasingly designed under unsteady flow assumptions. Consequently, one of the key aspects in the design of high-efficiency axial turbine stages is the control of wake flows originating from upstream stages. In a research study conducted by our research team entitled “Clocking effects on aerodynamics of a gas turbine low-pressure axial turbine, Part 2: Unsteady simulation”, the following questions related to blade clocking were addressed
?What distinguishes the wake flow within the blade passage from the background flow
?What is the instantaneous effect of the wake flow on turbulent kinetic energy (TKE) and flow entropy
?Based on which parameter(s) can the optimum clocking position be identified
?Are there limitations on the use of clocking for efficiency improvement
?What is the effective range of clocking influence on the aerodynamic efficiency of a simple-designed axial turbine
?How does the wake-flow kinematics change under optimum and the worst clocking positions
How do different clocking positions affect the lift coefficient, pressure loss, clocked stage output power, and the overall generated power
?What numerical requirements is required for clocking studies
Which turbulence model, Zonal-DES or SST k–ω, provides more reliable predictions of TKE? Does the outcome of clocking studies depend
?on the selected turbulence model
In this research work, a phenomenological analysis demonstrated that under optimum clocking position, the velocity over the suction surface of the blades increases, which in turn leads to an increase in the lift coefficient and the dynamic pressure at the blade-row exit. This increase in dynamic pressure, combined with lower-entropy flow at the blade-row outlet, can utilized for higher thrust generation in the downstream component (i.e., nozzle). However, the fundamental question remains: which flow phenomena are altered to produce this
?mechanism
To address this question and the other issues discussed above, and to access further details, interested readers are invited to consult the published article in the Aerospace Engineering journal (published by IMECHE), available at the following DOI
https://journals.sagepub.com/doi/10.1177/09544100231218738
