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The choke flutter is a fluid-structure interaction that can lead to the failure of fan or compressor blade in turbojet engines. In ultra high bypass ratio (UHBR) fans, the choke flutter appears at part-speed regimes and at low or negative incidence when a strong shock-wave chokes the blade to blade channel. The purpose of this study is to locate the main excitation sources and improving the understanding of the different work exchange mechanisms. This work contributes to avoiding deficient and dangerous fan design.

In this paper, an UHBR fan is analyzed using a time-linearized Reynolds-averaged Navier–Stokes equation solver to investigate the choke flutter. The steady-state and the imposed vibration (inter blade phase angle, reduced frequency and mode shape) are selected to be in choke flutter situation. Superposition principle induced by the linearization allow to decompose the blade in numerous small subsections to track the contribution of each local vibration to the global damping. All simulations have been performed on a two-dimensional blade to blade extraction.

Result analysis points to a restricted number of excitation sources at the trailing edge which induce a large part of the work exchange in a limited region of the airfoil. Main phenomena suspected are the shock-wave motion and the shock-wave/boundary layer interaction.

An original excitation source tracking methodology allowed by the linearized calculation is addressed and applied to a UHBR fan test case.

Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Council, Reports and Technical Memoranda of the United States National Advisory Committee for Aeronautics and publications of other similar Research Bodies as issued.

The bulk of jet engine noise developed at high powers arises from the turbulent mixing of the jet efflux in the surrounding air, as judged from model experiments, and has a continuous spectrum with a single flat maximum. The high frequency sound arises from fairly close to the orifice, and reaches its maximum intensity at fairly large acute angles to the jet direction. Lower frequency noise arises from lower down stream and its maxima make smaller acute angles with the jet axis. The possible origins are briefly discussed in view of Lighthill's theory and refraction effects. The most intensesound has a wave‐length of the order of three or four exit diameters, and originates between five and ten diameters from the orifice. A semi‐empirical rule of noise energy depending on the jet velocity to the eighth power and the jet diameter squared gives a rough estimate of the noise level for both cold and heated jets. Further noise from heated or supersonic jets may occur through eddies travelling at supersonic speed and so producing small Shockwaves. Model experiments have shown that interaction between shock‐wave configurations in choked jets and passing eddy trains generates sound and this initiates further eddies at the orifice. The directional properties of this sound are quite distinctive, the maximum being in the upstream direction. Methods of reducing jet noise are briefly discussed.

Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Council, Reports and Technical Notes of the United States National Advisory Committee for Aeronautics and publications of other similar Research Bodies as issued

Over the years, theories of the forces on bodies moving with purely subsonic or purely supersonic velocities through gases have been evolved as required by current aeronautical practice; the development of such theories has not proved unduly difficult. Moreover, the theories have been monitored and checked by corresponding experimental investigations. In view of the complexity of some of the subsonic work, it might have been expected that supersonic theory would prove intractable; in the event, it has proved that, in some respects at least, supersonic theory is simpler than subsonic. By contrast with these fields, studies of transonic phenomena have lagged badly. For one thing, experimental work at transonic speeds is comparatively recent: until the development of slotted or perforated walls for transonic tunnels, it used to be said that one could only test at M=l a model of infinitesimal size—anything finite choked the tunnel. On the theoretical side the investigator is faced with the study of a region involving mixed flows, different parts of the field obeying different laws, with an unspecified sonic line at the boundary. Clearly, even in steady conditions this is a problem of great complexity.

Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Council, Reports and Technical Memoranda of the United States National Advisory Committee for Aeronautics and publications of other similar Research Bodies as issued

Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Council, Reports and Technical Notes of the United States National Advisory Committee for Aeronautics and publications of other similar Research Bodies as issued

The transonic buffet is a complex aerodynamics phenomenon that imposes severe constraints on the design of high-speed vehicles, including for aircraft and space launchers. The origin of buffet is still debated in the literature, and the control of this phenomenon remains difficult. This paper aims to propose an original scenario to explain the origin of buffet, which in turn opens promising perspectives for its alleviation and attenuation.

This work relies on the use of numerical simulations, with the idea to reproduce the buffet phenomenon in a transonic aileron designed for small space launchers. Two numerical approaches are tested: unsteady Reynolds averaged Navier–Stokes (URANS) and large-eddy simulation (LES). The numerical predictions are first validated against available experimental data, before to be analysed in detail to identify the origin of buffet on the studied configuration. A complementary numerical study is then conducted to assess the possibility to delay the onset of buffet.

The buffet control strategy is based on wall cooling. By adequately choosing the wall temperature, this work shows that it is feasible to delay the emergence of buffet. More precisely, this paper highlights the crucial role of the subsonic flow inside the boundary layer, showing the existence of upstream travelling pressure waves that are responsible for the flow coupling between both sides of the airfoil, at the origin of the buffet phenomenon.

This paper proposes a new scenario to explain the origin of buffet, based on the use of a Fanno and Rayleigh flow analogies. This approach is used to design a control solution based on a modification of the wall temperature, showing very promising results.

Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Council, Reports and Technical Memoranda of the United States National Advisory Committee for Aeronautics and publications of other similar Research Bodies as issued.

IN our report of the tenth annual meeting of the Institute of the Aeronautical Sciences we shall not follow precisely the order in which the sessions occurred nor at all times classify the papers in exactly the manner of the meeting. Unfortunately, certain of the papers presented will not be found in our review owing to lack of preprints, but this in no way reflects on the value or timeliness of the papers omitted in the review.