Print Email Facebook Twitter Effect of aeroelasticity on the acoustic signature of TOP contoured rocket nozzles in overexpanded conditions Title Effect of aeroelasticity on the acoustic signature of TOP contoured rocket nozzles in overexpanded conditions Author Formidabile, Martina (TU Delft Aerospace Engineering; TU Delft Flight Performance and Propulsion; TU Delft Aerodynamics) Contributor Baars, W.J. (mentor) Schrijer, F.F.J. (mentor) van Oudheusden, B.W. (graduation committee) Langella, I. (graduation committee) Degree granting institution Delft University of Technology Programme Aerospace Engineering Date 2023-05-22 Abstract TOP contoured nozzles, with large area-ratios, are commonly employed in rocket propulsion systems as they feature an excellent thrust-to-weight ratio. A significant shortcoming to this design is that, during the startup and shutdown transients of a LRE, the internal nozzle flow progresses through a series of overexpanded flow states - Free Shock Separation (FSS) and Restricted Shock Separation (RSS), which produce critical loads associated with SWBLI and asymmetric flow separation. Exacerbated by FSI, this operational phase is known to generate the highest vibroacoustic loads at which payload and vehicle structures are subjected to when the engine is operated at off-design conditions. Motivated by the importance of understanding how the interaction between the developing flow and the vibrating nozzle walls has an effect on supersonic noise generation and propagation, this work has studied the effect that wall compliancy has on the vibroacoustic loading of TOP contoured nozzles. This is demonstrated by means of cold flow tests carried out in the High Speed Laboratories of the Delft University of Technology on a stiff-walled aluminum nozzle, which serves as a baseline test case, and on a urethane-based compliant walled nozzle. Tests are conducted under comparable flow conditions and test parameters are measured by means of acoustic and optical techniques. Simultaneous recordings are performed and include the nozzle-wall deformation, by means of stereoscopic tracking of tracers on the nozzle lip, the imprint of the near-field acoustic signature, by means of arrays of pressure-microphones, and Schlieren imaging of the jet plume.Measurement data allows for a Fourier decomposition of the nozzle lip displacement and of the acoustic pressure field in azimuth. Reconstruction of the instantaneous plume development enables the identification of the main flow structures responsible for noise generation. Comparison of results between the two test articles highlights a different spectral content and directivity pattern. Correlation between the structural displacements and the acoustic signal, together with the use of DMD, quantitatively aids the investigation of how FSI has an impact on the generation of an aeroelastic tone at 180 Hz. Findings suggest that its production is the result of the periodic thickening and thinning of the shear layer owing to the heightened flapping motion of the nozzle lip preceding RSS transition, driven by an intensified shock foot instability. Subject Rocket propulsionAcoustic instabilitiesGasdynamicsSupersonic jet noiseShock wave boundary layer interactionFree shock separationRestricted shock separationOverexpanded flow operationsFluid-structure interactionCompliant nozzleStructural DynamicsSchlieren imagingLip trackingAcoustic sensing To reference this document use: https://doi.org/10.4233/uuid:64df2f9c-c7e5-4350-9094-3ee15946dfb2 Part of collection Student theses Document type master thesis Rights © 2023 Martina Formidabile Files PDF Thesis_M_Formidabile.pdf 86.36 MB Close viewer /islandora/object/uuid:64df2f9c-c7e5-4350-9094-3ee15946dfb2/datastream/OBJ/view