Abstract
Stage stacking methods commonly use a one-dimensional (1D) through flow analysis at the mean line to design individual axial compressor stages and stack these to form a multistage axial compressor. This phase of design exerts a great influence on each stage's pressure and temperature ratio. The design process for an individual stage is usually guided by design values and rules developed in previous designs. This study develops a 1D stage un-stacking method (SUSM), which uses a minimal set of data from an actual axial compressor, while reducing the needed number of assumptions. Proceeding from the premise that an actual axial compressor design fulfills all thermodynamic requirements, velocity triangle requirements and design guidelines simultaneously, this proposed SUSM calculates the pressure, temperature, velocities and flow angles as a set of dependent data at each stage of the axial compressor. In approximating a possible axial compressor design for the LM2500 gas turbine that achieves the known pressure ratio distribution, the suggested stage loading coefficient (SLC) distribution is more appropriately considered an initial well-informed estimate and further improvements to this SUSM are needed to infer the actual SLC distributions used.
Highlights
The need for greater efficiency drives each new gas turbine model towards higher overall pressure ratios and power outputs, inevitably keeping the gas turbine relevant
The distribution of stage pressure ratios is based on fully isentropic compression using specific entropy as a function of temperature and pressure applied to each stage (Pressure ratio model 3)
5 Conclusion This paper presents a stage un-stacking method that determines the velocities and flow angles within a multistage axial compressor
Summary
The need for greater efficiency drives each new gas turbine model towards higher overall pressure ratios and power outputs, inevitably keeping the gas turbine relevant. The compressor is often the axial flow design, to pass higher mass flow rates through a relatively smaller frontal area and achieve generally higher stage pressure ratios with lower losses compared to the centrifugal design. With each successive design delivering higher overall pressure ratios, the relevance of the multistage axial flow compressor is not diminishing. The design process for an axial compressor, from simple to challenging are: 1-dimensional (1D) analysis at the mean line, 2dimensional (2D) cascade analysis (where the blade rows are unwrapped from the rotational axis), 2D streamline curvature, 1D analysis of radial variation across the blade span resulting in span-wise blade twist angles and 3-dimensional (3D) analysis to simulate the challenging actual turbulent flows at the blade root and tip (which contribute heavily to losses). The 1D analysis at the mean line exerts great influence on the design of an axial compressor because, at this design phase, each stage’s pressure and temperature are defined before detailed design work begins and assembled together
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