This paper is the second part of a series of three papers dedicated to the prediction of low-speed interaction noise of an isolated Contra-Rotating Open Rotor (CROR). The objective is to investigate the URANS chorochronic approach for computing the unsteady flow across both rotors. The stress is to be put on the correct description and propagation of the wake deficit, which is essential for capturing the unsteady loading onto the rear row and thus the resulting interaction noise. Chorochronic methods are attractive because they require the computation of a single channel only and thus are less costly than full-annulus CFD computations (such as sliding mesh or Chimera techniques). Therefore, the chorochronic technique is used in this study to investigate various mesh topologies. It is shown that the method presents very good agreement with experimental data in absolute levels at a very reasonable cost. Nomenclature BPF= Blade Passage Frequency mR = Rear rotor tones frequency, m×BPF (rear rotor) nF = Front rotor tones frequency, n×BPF (front rotor) nF+mR = Rotor-to-rotor tones frequency, n×BPF (front rotor) + m×BPF (rear rotor) N i = number of blades of the row i R i = radius of rotor i RPM = Revolutions Per Minute SPL = Sound Pressure Level T choro = Chorochronic period T i = Relative period of row i Ω i = rotational speed of blade row i

Purpose-The purpose of this paper is to explore a methodology that allows to represent turbomachinery rotating parts by replacing the blades with a body force field. The objective is to capture interactions between a fan and an air intake at reduced cost, as compared to full annulus unsteady computations. Design/methodology/approach-The blade effects on the flow are taken into account by adding source terms to the Navier-Stokes equations. These source terms give the proper amount of flow turning, entropy, and blockage to the flow. Two different approaches are compared: the source terms can be computed using an analytic model, or they can directly be extracted from RANS computations with the blade's geometry. Findings-The methodology is first applied to an isolated rotor test case, which allows to show that blockage effects have a strong impact on the performance of the rotor. It is also found that the analytic body force model underestimates the mass flow in the blade row for choked conditions. Finally, the body force approach is used to capture the coupling between a fan and an air intake at high angle of attacks. A comparison with full annulus unsteady computations shows that the model adequately captures the potential effects of the fan on the air intake. Originality/value-To the authors' knowledge, it is the first time that the analytic model used in this paper is combined with the blockage source terms. Furthermore, the capability of the model to deal with flows in choked conditions was never assessed.

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With the advent of high bypass ratio turbofan engines of increasing size, new nacelle designs with shorter air intakes have to be considered, creating new aerodynamic interactions with the fan. This paper focuses on a numerical strategy known as Body Force Modeling, in which engine components are modeled and taken into account using source terms in the RANS equation. This approach allows to simulate these interactions with an accuracy comparable to full 360° unsteady simulations, but at a fraction of the cost. Different formulations for the body forces are proposed and applied to different nacelle test cases of varying intake length. Using full annulus unsteady computations as validation data, it is shown that the body force approach allows to capture inlet design effects on in-plane forces and on nacelle flow separation.

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