Abstract
Aeroengine fans and compressors increasingly operate subject to inlet distortion in the transonic flow regime. In this paper, innovations to low-order numerical modeling of fans and compressors via volumetric source terms (body forces) are presented. The approach builds upon past work to accommodate any axial fan/compressor geometry and ensures accurate work input and efficiency prediction across a range of flow coefficients. In particular, the efficiency drop-off near choke is captured. The model for a particular blade row is calibrated using data from single-passage bladed computations. Compared to full-wheel unsteady computations which include the fan/compressor blades, the source term model approach can reduce computational cost by at least two orders of magnitude through a combination of reducing grid resolution and, critically, eliminating the need for a time-resolved approach. The approach is applied to NASA stage 67. For uniform flow, at 90% corrected speed and peak-efficiency, the body force model is able to predict the total-to-total pressure rise coefficient of the stage to within 1.43% and the isentropic efficiency to within 0.03%. With a 120∘ sector of reduced inlet total pressure, distortion transfer through the machine is well-captured and the associated efficiency penalty predicted with less than 2.7% error.
Highlights
In the preliminary design of compressors, maintaining low computational cost for numerical simulation of the blade aerodynamics is paramount
Λ = 0.27 Λ=0 Experimental values in the rotor and along the stator leading edge. This is expected, as in the rotor, at increasing radius, there is an associated increase in relative Mach number while in the stator the swirl and the Mach number are highest around the leading edge
The largest error is expected to be found in the total pressure versus flow coefficient characteristic as it is strongly dependent on the accuracy of both the normal and parallel force models
Summary
In the preliminary design of compressors, maintaining low computational cost for numerical simulation of the blade aerodynamics is paramount. A few recent examples which do not form an exhaustive list include the following: (1) Defoe and Spakovszky investigated the generation and propagation of fan rotor shock noise due to inlet swirl distortion [2, 3], (2) Thollet et al used body force modeling to reduce the computational cost in studying intake-fan interaction [4], (3) Defoe et al examined low-speed boundary-layer-ingesting fan and compressor performance using a nonaxisymmetric throughflow method [1], and (4) Guo and Hu observed multistage compressor performance in the presence of inlet flow distortion [5]. The compressor performance metrics and flow field details are compared against previously published experimental data as well as full-annulus, bladed computations
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