Aerodynamic and Aeroelastic Effects of Design-Based Geometry Variations on a Low-Pressure Compressor

Abstract

In modern aircraft engines, the low-pressure compressor (LPC) is subjected to a flow characterized by strong wakes and secondary flows from the upstream fan. This concerns ultra-high bypass ratio (UHBR) turbofan engines, in particular. This paper presents the aerodynamic and aeroelastic sensitivities of parametric variations on the LPC, driven by the design considerations in the upstream fan. The goal of this investigation was to determine the influence of design-based geometry parameter variations on the LPC performance under realistic inlet flow distributions and the presence of an s-duct. Aerodynamic simulations are conducted at the design and off-design operating points with the fan outflow as the inlet boundary conditions. Based on the aerodynamic results, time-linearized unsteady simulations are conducted to evaluate the vibration amplitude at the resonance operating points. First, the bypass ratio is varied by reducing the channel height of the LPC. The LPC efficiency decreases by up to 1.7% due to the increase in blockage of the core flow. The forced response amplitude of the rotor decreases with increasing bypass ratio due to increased aerodynamic damping. Secondly, the fan cavity leakage flow is considered as it directly affects the near hub fan flow and thus the inflow of the LPC. This results in an increased total-pressure loss for the s-duct due to mixing losses. The additional mixing redistributes the flow at the s-duct exit leading to a total-pressure loss reduction of 4.3% in the first rotor at design point. This effect is altered at off-design conditions. The vibration amplitude at low speed resonance points is increased by 19% for the first torsion and 26% for second bending. Thirdly, sweep and lean are applied to the inlet guide vane (IGV) upstream of the LPC. Despite the s-duct and the variable inlet guide vane (VIGV) affecting the flow, the three-dimensional blade design achieves aerodynamic and aeroelastic improvements of rotor 1 at off-design. The total-pressure loss reduces by up to 18% and the resonance amplitude more than 10%. Only negligible improvements for rotor 1 are present at the design point. In a fourth step, the influence of axial gap size between the stator and the rotor rows in the LPC is examined in the range of small variations which shows no distinct aerodynamic and aeroelastic sensitivities. This finding not only supports previous studies, but it also suggests a correlation between mode shapes and locally increased excitaion with increasing axial gap size. As a result, potential design improvements in future fan-compressor design are suggested.

Influence of Axial Gaps on Forced Response of Different Mode Shapes in a Low-Pressure Compressor

“…The forced-response amplitude is determined by the ratio of the aerodynamic forcing work to the energy dissipated by the aerodynamic damping. As documented by Eggers et al (2020), the aerodynamic damping exhibits only 0..2% variation for the axial-gap changes considered. For this reason, the damping is omitted in this study and only the unsteady aerodynamic work per cycle is compared as a representative quantity of the forced-response behaviour.…”

“…The gap varies by ±10% for the other configurations. Additional details can be found in (Eggers et al, 2020).…”

“…A previous study was initiated to investigate aerodynamic and aeroelastic performance in a low-pressure compressor of a ultra-high bypass-ratio (UHBR) engine (Eggers et al, 2020). Three different axial gaps were studied under the influence of realistic UHBR-specific inflow.…”

“…• Extension of the parametric study by Eggers et al (2020) to include different operating points and mode shapes • Quantitative comparison of the unsteady work on the blades with respect to an axial-gap variation • Detailed analysis of the unsteady pressure and aerodynamic work • Identification of deterministic parameters to predict forced-response behaviour…”

Device for Contact Measurement of Turbine Blade Geometry in Robotic Grinding Process

“…Therefore, the blade manufacturing process is strictly controlled to ensure its repeatability, and the blades’ geometric properties are subject to rigorous assessment [ 2 ]. Similar control is performed during the blade repair process, which extends the life of the system and increases its economic efficiency [ 3 , 4 ]. An important aspect in choosing the method for geometric parameter control is the fact that the final shape of the blade depends on the final grinding operation.…”