We present an investigation of the acoustic scattering due to the presence of a flat plate in the vicinity of a turbulent subsonic jet. Experiments have been performed to measure changes in the velocity and sound fields for Mach numbers ranging from 0.4 to 0.6, and for distances between the plate and the jet axis ranging from 1 to 2 jet diameters. Results show only very slight changes in the mean flow induced by the plate, and no differences in the velocity fluctuation amplitudes on the jet centreline, suggesting that wave-packet models derived for jets without installation effects may be representative of the installed case, at least for the jet-plate distances considered here. The acoustic results, on the other hand, include a significant increase in the low-frequency sound radiation, and phase opposition between the shielded and unshielded sides of the plate. There is an exponential decay of the scattered sound with increasing jet-plate distance, suggesting that low-frequency radiation is due to the scattering of evanescent hydrodynamic wavepackets in the jet near field. To model this phenomenon, we calculate sound generation from wave-packet sources in two ways: on one hand we use a tailored Greens function that accounts for the presence of a semi-infinite, rigid flat plate; and, on the other, we solve numerically the Helmholtz equation, with boundary conditions representative of a finite flat plate, using a fast multipole boundary element method. In agreement with the experimental measurements, numerical calculations capture the phase opposition between shielded and unshielded sides, and the scattered sound depends exponentially on the position of the plate. This exponential dependence is related to non-compact effects associated with wavepackets, as compact sources would lead to an algebraic dependence. Acoustic pressure directivities computed for the finite and semi-infinite flat plates agree well where acoustic reflection and diffraction from the trailing edge of the plates are concerned. However, additional diffraction effects associated with the leading and lateral edges of the finite plate, and which take the form of multiple lobes in the directivity, are illustrated by the comparison. As the plate dimensions are increased, i.e. the Helmholtz number is increased, the solution approaches that obtained for the semi-infinite plate.3332465166531Curle, N., The influence of solid boundaries upon aerodynamic sound (1955) Proceedings of the Royal Society A, 231, pp. 505-514Lighthill, M.J., On sound generated aerodynamically. I. General theory (1952) Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, pp. 564-587Ffowcs Williams, J.E., Hall, L.H., Aerodynamic sound generation by turbulent flow in the vicinity of a scattering half plane (1970) Journal of Fluid Mechanics, 40 (4), pp. 657-670Macdonald, H.M., A class of diffraction problems (1915) Proceedings of the London Mathematical Society, 2 (1), p. 410Crow, S.C., Acoustic gain of a turbulent jet (1972) Physical Society Meeting, 6. , University of Colorado, Boulder, Paper IEFfowcs Williams, J.E., Kempton, A.J., The noise from the large-scale structure of a jet (1978) Journal of Fluid Mechanics, 84 (4), pp. 673-694Mankbadi, R., Liu, J., Sound generated aerodynamically revisited large-scale structures in a turbulent jet as a source of sound (1984) Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences, 311 (1516), pp. 183-217Cavalieri, A.V.G., Jordan, P., Colonius, T., Gervais, Y., Axisymmetric superdirectivity in subsonic jets (2012) Journal of Fluid Mechanics, 704, p. 388Suzuki, T., Colonius, T., Instability waves in a subsonic round jet detected using a near-field phased microphone array (2006) Journal of Fluid Mechanics, 565, pp. 197-226Gudmundsson, K., Colonius, T., Instability wave models for the near-field fluctuations of turbulent jets (2011) Journal of Fluid Mechanics, 689, pp. 97-128Cavalieri, A.V.G., Rodríguez, D., Jordan, P., Colonius, T., Gervais, Y., Wavepackets in the velocity field of turbulent jets (2013) Journal of Fluid Mechanics, 730, pp. 559-592Jordan, P., Colonius, T., Wave packets and turbulent jet noise (2013) Annual Review of Fluid Mechanics, 45, pp. 173-195Mead, C.J., Strange, P.J.R., Under-wing installation effects on jet noise at sideline (1998) 4th AIAA/CEAS Aeroacoustics Conference and Exhibit, , Toulouse, FranceLawrence, J.L.T., Azarpeyvand, M., Self, R.H., Interaction between a flat plate and a circular subsonic jet (2011) 17th AIAA/CEAS Aeroacoustics Conference and Exhibit, , Portland, OR, USAWolf, W.R., Lele, S.K., Wideband fast multipole boundary element method: Application to acoustic scattering from aerodynamic bodies (2011) International Journal for Numerical Methods in Fluids, 67 (12), pp. 2108-2129Batchelor, G.K., Gill, A.E., Analysis of the stability of axisymmetric jets (1962) Journal of Fluid Mechanics, 14 (4), pp. 529-551Crighton, D.G., Huerre, P., Shear-layer pressure fluctuations and superdirective acoustic sources (1990) Journal of Fluid Mechanics, 220, pp. 355-368Reba, R., Narayanan, S., Colonius, T., Wave-packet models for large-scale mixing noise (2010) International Journal of Aeroacoustics, 9 (4), pp. 533-558Maestrello, L., Statistical properties of the sound and source fields of an axisymmetric jet (1977) American Institute of Aeronautics and Astronautics Conference, 1Zhang, S., Jin, J.M., (1996) Computation of Special Functions, , John Wiley Somerset, NJCrighton, D.G., Dowling, A.P., Ffowcs-Williams, J.E., Heckl, M., Leppington, F.G., (1992) Modern Methods in Analytical Acoustics: Lecture Notes, , Springer, LondonSonneveld, P., A fast Lanczos-type solver for nonsymmetric linear systems (1989) SIAM Journal on Scientific and Statistical Computing, 10 (1), pp. 36-52. , CGSAssier, R.C., Peake, N., On the diffraction of acoustic waves by a quarter-plane (2012) Wave Motion, 49, pp. 64-82Crighton, D.G., Leppington, F.G., On the scattering of aerodynamic noise (1971) Journal of Fluid Mechanics, 46 (3), pp. 577-597Wolf, W.R., Azevedo, J.L.F., Lele, S.K., Convective effects and the role of quadrupole sources for aerofoil aeroacoustics (2012) Journal of Fluid Mechanics, 708, pp. 502-538Ffowcs Williams, J.E., Hawkings, D.L., Sound generation by turbulence and surface in arbitrary motion (1969) Philosophical Transaction of the Royal Society of London. Series A, Mathematical and Physical Sciences, 264, pp. 321-342Fuchs, H.V., Michel, U., Experimental evidence of turbulent source coherence affecting jet noise (1978) AIAA Journal, 16 (9), pp. 871-872Juvé, D., Sunyach, M., Comte-Bellot, G., Filtered azimuthal correlations in the acoustic far field of a subsonic jet (1979) AIAA Journal, 17, p. 112Guitton, A., Jordan, P., Laurendeau, E., Delville, J., Velocity dependence of the near pressure field of subsonic jets: Understanding the associated source mechanisms (2007) 13th AIAA/CEAS Aeroacoustics Conference and Exhibit, , Rome, ItalyTinney, C.E., Jordan, P., The near pressure field of co-axial subsonic jets (2008) Journal of Fluid Mechanics, 611, pp. 175-204