Experimental Validation of a Cascade Response Function for Fan Broadband Noise Predictions

Abstract

The present paper is aimed at assessing an analytical prediction model for the broadband noise produced by the impingement of turbulence on a cascade, using a dedicated experiment. The model is a strip-theory approach based on a previously published formulation of the unsteady blade loading for a rectilinear cascade. The experimental setup is made of a single stationary cascade of vanes mounted downstream of a turbulence grid in an annular duct, at the exit of an open-jet anechoic wind tunnel. The statistical parameters of the turbulence measured with hot-wire anemometry are used as input data in the model. The in-duct predicted downstream acoustic power is compared with the measured power obtained from the far-field acoustic pressure. Measured and predicted variations of the acoustic power with the number of vanes of the cascade and with the turbulence intensity are found to be in good agreement. It is concluded that the analytical approach succeeds in highlighting three-dimensional effects and is promising for further comparisons in more complex annular configurations. = squared norm of the duct eigenfunction E m; = microphone angle in the horizontal plane P containing the center of the exhaust section = turbulence integral length scale 0 = exponential correction factor of the turbulence spectrum 0 = fluid density = interblade phase angle uu ! = power spectral density of the streamwise velocity ww K; r = three-dimensional wave-number turbulence spectrum for the vane normal velocity component divided by u 2 rmŝ ' = sweep angle in the duct reference framê = stagger angle in the duct reference frame m;= eigenvalue of the mode m;

Experimental and Numerical Investigation of Turbulence-Airfoil Noise Reduction Using Wavy Edges

“…The present methodology will also be extended to an annular cascade configuration in order to assess the solutions proposed in a CAA benchmark 52 limited to harmonic gusts. Then the interaction between a HIT and a cascade in an annular duct 53 will be numerically investigated, in order to finally apply the methodology to realistic rotor/stator broadband noise problems by chaining the CAA to RANS or LES rotor wake computations.…”

Numerical Predictions of Turbulence-Cascade Interaction Noise Using CAA with a Stochastic Model

“…It can be noticed that the turbulence-flow characteristics generated by the turbulence grid are slightly modified when changing the cascade vane number. (The present values for cascade C2 used here are expected to be more representative than those reported in [18], in which the same values were considered for grids C1 and C2. )…”

“…The Amiet-based results are compared to the solutions obtained by Posson and Roger [18] and Zhang et al [25] in Fig. 7, and to the experiment too.…”

“…The first validation case is devoted to a turbulence-cascade interaction using a turbulence grid in a purely axial mean flow, related to an experiment proposed by ECL [18]. A picture of the anechoic open-jet wind tunnel with an outlet view of the model and a sketch of the test rig are shown in Fig.…”

“…Then, the method is applied to the simulation of turbulence/ cascade-interaction noise on two selected configurations: 1) a turbulence/annular-cascade interaction in a uniform axial mean flow, related to a laboratory experiment performed in the anechoic open-jet wind tunnel of École Centrale de Lyon (ECL) [18] and chosen as a fundamental case in the framework of a recent workshop on broadband-turbofan-noise prediction [19]; and 2) a turbulence/ annular-cascade interaction in a swirling mean flow, related to a benchmark proposed by Atassi and Vinogradov [20], with a reference solution issued from the frequency-domain linearized Euler code developed by Atassi et al [21].…”