An image analysis method is developed and applied to shadowgraph images of supersonic jet flow to measure shock front propagation angles at numerous interrogation points distributed throughout the quiescent region outside of the jet shear layer. These shock fronts manifest in acoustic measurements of jet noise as steepened temporal waveforms that have been linked to the perception of crackle. The analysis method uses the Radon transform to quantitatively determine a local shock front propagation angle at each point. The dataset of angles is subsequently used to determine the locations and convection velocities of the sources inside the jet shear layer. The results indicate that the shock-like waves emerge immediately from the jet shear layer and are created by the supersonic convection of coherent structures. The statistical distribution of convection velocities follows an extreme value distribution, indicating that the shock front emitting sources are maxima of the underlying turbulence. A noise reduction method known to reduce the convection velocities in the jet shear layer is applied to the jet to investigate the effect on the shock front emission. The shock front angles change in concert with the reduction in convection velocity giving further evidence that the source of crackle is a flow field event.

This paper describes the experimental study of the noise generating characteristics of high-temperature, shock-containing jets emanating from conic-section, converging-diverging (C-D) nozzles. Conic C-D nozzles consist of two conic sections, one contracting and the other expanding, joined to form a supersonic nozzle with a very sharp radius of curvature at the nozzle throat. An experiment is conducted in which temporally resolved flow-field measurements are acquired simultaneously with near-field and far-field acoustics to allow investigation of the turbulence associated with noise generation. The MHz rate PIV system and its synchronization with acoustic measurements is described along with methods for data analysis. General acoustic results are presented to characterize the spectral content present, and preliminary results on the measured turbulence structures are discussed.

In this paper, we shall examine the feasibility of using time-resolved hybrid RANS-LES (HRLES) simulation data to perform noise source localization studies on a hot jet from a conic nozzle operating at pressure matched conditions. The source localization will be performed using a traditional delay-and-sum beamforming technique. This technique requires time-resolved data on a phased array of microphones located in the acoustic farfield of the jet; this data will be obtained by coupling the HRLES simulation with a Ffowcs Williams and Hawkings equation noise prediction code. Using insights gained from experimental beamforming, we shall show that beamforming using CFD data is a feasible, and potentially less expensive and time-saving, alternative to constructing complicated phased array systems for performing these calculations on experimental data. I. Background and MotivationNoise from supersonic jets falls primarily into two categories, either turbulent mixing noise or shock noise. Of these two, turbulent mixing noise is comprised of two sources, both of which are broadband in nature: (a) the eddy Mach wave radiation which propagates downstream relative to the jet flow direction, and (b) fine scale turbulence which is omni-directional. On the other hand, shock noise can be either narrowband (also called jet screech) or broadband (called broadband shock associated noise, or BSAN), and propagates towards the sideline or upstream direction relative to the jet flow. Shock noise most commonly occurs when a convergent-divergent nozzle is operated at off-design conditions. However, jets exhausting from military nozzles typically contain shocks even when operated at design conditions; this is primarily because the internal contour of these nozzles are not shaped in order to ensure a smooth expansion of the gas.Jet noise contributes significantly to noise-induced hearing loss, structural degradation of airframes, and restrictions to maintenance, testing, and training schedules due to noise pollution of communities surrounding military installations. To this end, it is imperative to gain a better understanding of jet noise generation mechanisms in a turbulent flow. Such an understanding is essential if one is to construct predictive models for jet noise. One approach that has been considered is the beamforming technique using a phased array of microphones. 1 This technique has been shown to provide an estimate of the distribution of noise sources in a

Monitoring of the effects of hydrocarbon pipeline blockages such as may be caused by hydrates and waxes is receiving a higher level of consideration as the distributed sensing capability offered by the use of fibre optic technology matures. The extent of the hydrate or wax formation problem increases with pipeline length through the effects of cooling. The challenge is significantly greater when assuring flows in deep water and remote subsea locations. Commercially available strain and temperature sensing equipment such as discrete FBGs (Fibre Bragg Gratings) and fully distributed sensing techniques such as Raman DTS (distributed temperature sensor) and Brillouin OTDR (optical time domain reflectometry) typically offer sensing lengths of the order of 20–30km. Whilst this is in many instances a useful length, it is not sufficient to be able to monitor the whole of a pipeline which may be several hundreds of kilometres in length. The authors have developed and demonstrated a method for extending the reach of a Brillouin OTDR interrogating system such that sensing sections of conventional length (approximately 25km) can be successfully interrogated from distances well in excess of 100km without having to compromise on the performance. With a single instrument, more than 250km of sensing fibre can be monitored to within 1.5 metre resolution. By this means, temperature and strain profiles may be measured for the entire pipeline length which will enable active flow assurance measures to be taken including identifying the presence, nature and extent of blockages as they form. Consequently, any corrective action taken by the pipeline operators will be on an informed basis (such as the injection of an optimised quantity of inhibitor), and will incur a significantly lower level of risk than is currently possible. This paper describes the technology which has been developed to meet this requirement and provides results of simulated pipeline blockage effects which demonstrate this.

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