Non-uniform Radial Meanline Method for Off-design Performance Estimation of Multistage Axial Compressors


Book Description

The increasing use of renewable energy sources necessitates power-generating gas turbines capable of frequently and rapidly starting up to supplement the energy supply when renewable sources alone cannot meet demand [1], [21. This makes the off-design performance of such gas turbines more important as they spend more of their operational life off the design point. Currently off-design performance cannot be estimated with high fidelity until late in the gas turbine compressor design process at which point the design is largely fixed and only limited changes can be made. This thesis presents a Non-Uniform Radial Meanline method for multistage axial compressor off-design performance estimation, capturing the transfer of radial flow non-uniformity and its impact on compressor blade row performance. This method enables the high-fidelity characterization of blade row performance and the stage matching of multistage compressors with non-uniformity effects included. A new representation of non-uniform radial flow profiles using orthonormal basis functions was developed to provide a compact representation suitable for inclusion in a one-dimensional performance estimation method. The link between radial flow non-uniformity and compressor blade row performance was characterized using three-dimensional embedded stage calculations. An initial implementation of the Non-Uniform Radial Meanline method was demonstrated for different compressor inlet non-uniformities. The computations show that the new approach provides an effective means of incorporating radial flow non-uniformity into a one-dimensional compressor performance estimation method.




Axial and Centrifugal Compressor Mean Line Flow Analysis Method


Book Description

This paper describes a method to estimate key aerodynamic parameters of single and multistage axial and centrifugal compressors. This mean-line compressor code COMDES provides the capability of sizing single and multistage compressors quickly during the conceptual design process. Based on the compressible fluid flow equations and the Euler equation, the code can estimate rotor inlet and exit blade angles when run in the design mode. The design point rotor efficiency and stator losses are inputs to the code, and are modeled at off design. When run in the off-design analysis mode, it can be used to generate performance maps based on simple models for losses due to rotor incidence and inlet guide vane reset angle. The code can provide an improved understanding of basic aerodynamic parameters such as diffusion factor, loading levels and incidence, when matching multistage compressor blade rows at design and at part-speed operation. Rotor loading levels and relative velocity ratio are correlated to the onset of compressor surge. NASA Stage 37 and the three-stage NASA 74-A axial compressors were analyzed and the results compared to test data. The code has been used to generate the performance map for the NASA 76-B three-stage axial compressor featuring variable geometry. The compressor stages were aerodynamically matched at off-design speeds by adjusting the variable inlet guide vane and variable stator geometry angles to control the rotor diffusion factor and incidence angles.




Analysis of the Effects of Design Pressure Ratio Per Stage and Off-design Efficiency on the Operating Range of Multistage Axial-flow Compressors


Book Description

Multistage compressors composed of high-pressure-ratio stages have higher over-all off-design efficiencies and a wider operating range than those made up of low-pressure-ratio stages if the blade-row efficiency curves for the two cases are assumed to be somewhat similar.







Axial and Centrifugal Compressor Mean Line Flow Analysis Method


Book Description

This paper describes a method to estimate key aerodynamic parameters of single and multistage axial and centrifugal compressors. This mean-line compressor code COMDES provides the capability of sizing single and multistage compressors quickly during the conceptual design process. Based on the compressible fluid flow equations and the Euler equation, the code can estimate rotor inlet and exit blade angles when run in the design mode. The design point rotor efficiency and stator losses are inputs to the code, and are modeled at off design. When run in the off-design analysis mode, it can be used to generate performance maps based on simple models for losses due to rotor incidence and inlet guide vane reset angle. The code can provide an improved understanding of basic aerodynamic parameters such as diffusion factor, loading levels and incidence, when matching multistage compressor blade rows at design and at part-speed operation. Rotor loading levels and relative velocity ratio are correlated to the onset of compressor surge. NASA Stage 37 and the three-stage NASA 74-A axial compressors were analyzed and the results compared to test data. The code has been used to generate the performance map for the NASA 76-B three-stage axial compressor featuring variable geometry. The compressor stages were aerodynamically matched at off-design speeds by adjusting the variable inlet guide vane and variable stator geometry angles to control the rotor diffusion factor and incidence angles. Veres, Joseph P. Glenn Research Center TURBOCOMPRESSORS; FLUID FLOW; COMPUTATIONAL FLUID DYNAMICS; COMPRESSIBLE FLUIDS; DESIGN ANALYSIS; GUIDE VANES; CENTRIFUGAL COMPRESSORS; SURGES; DIFFUSION; ROTORS; STATORS




Development of a Methodology to Estimate Aero-performance and Aero-operability Limits of a Multistage Axial Flow Compressor for Use in Preliminary Design


Book Description

The preliminary design of multistage axial compressors in gas turbine engines is typically accomplished with mean-line methods. These methods, which rely on empirical correlations, estimate compressor performance well near the design point, but may become less reliable off-design. For land-based applications of gas turbine engines, off-design performance estimates are becoming increasingly important, as turbine plant operators desire peaking or load-following capabilities and hot-day operability. The current work implements a one-dimensional stage stacking procedure, including a new blockage term, which is used to estimate off-design compressor performance and operability range of a 13-stage axial compressor used for power generation. The procedure utilizes stage characteristics which are constructed from computational fluid dynamics (CFD) simulations of groups of stages. The stage stacking estimates match well with CFD results. These CFD results are used to assess a metric which estimates the stall limiting stages.




Incorporation of High-fidelity Flow Field Information Into Preliminary Design of Multi-stage Axial Compressors


Book Description

This thesis establishes an axisymmetric methodology that incorporates pre-performed high-fidelity CFD into the performance estimation of multi-stage axial compressors during preliminary design. Its key differentiator is that radial non-uniformity, inferred from three-dimensional CFD and represented using orthonormal basis functions, replaces empirical correlations of blockage, loss, and deviation as well as simplified models of flow features, such as boundary-layer growth, spanwise mixing, and endwall-corner separation. The methodology includes the effects of changes in radial non-uniformity and in blade geometry on the axisymmetric flow field. The approach can supersede current throughflow methods, increasing the fidelity of preliminary design. The primary impact of the methodology is a new capability for power gas turbine compressors to rapidly assess off-design matching at different spanwise locations along the blade height, enabling early-design choices, such as the annulus-area scheduling, based on the fidelity of CFD. Over a range of off-design conditions from near stall to near choke, the massflow capacity of a four-stage compressor was estimated within 1.2% and its efficiency within 1.5 percentage points compared to CFD at equal loading. The estimation of quasi-one-dimensional performance and the characterization of the flow close to the endwalls are improved relative to estimations of a legacy streamline curvature method since radial non-uniformity is inferred from high-fidelity flow field information. The methodology is demonstrated to be suitable for incorporation into compressor design systems.