![]() ![]() The other two buffet flows have been intentionally influenced by an artificial acoustic source installed downstream of the test section to investigate the behavior of the interaction to upstream-propagating disturbances generated by a defined source of noise. ![]() One flow exhibits a sinusoidal streamwise oscillation of the shock wave only due to an acoustic feedback loop formed by the shock wave and the trailing-edge noise. Therefore, the TR-SPIV results are analyzed for three buffet flows. Results from wind-tunnel experiments with a variation of the freestream Mach number at Reynolds numbers ranging from 2.55 to 2.79 × 10 6 are analyzed regarding the origin and nature of the unsteady shock–boundary layer interaction. The dynamic shock wave–boundary layer interaction is one of the most essential features of this unsteady flow causing a distinct oscillation of the flow field. Schrijer, B.W.Time-resolved stereo particle-image velocimetry (TR-SPIV) and unsteady pressure measurements are used to analyze the unsteady flow over a supercritical DRA-2303 airfoil in transonic flow. Graphic abstract: Įxperiments in Fluids: experimental methods and their applications to fluid flow, 62 (10) Part of collection In contrast, the analysis of the vortex dynamics in the trailing edge area revealed that vortices shed at the shock foot, which convect downstream in an area detached from the airfoil surface, cannot be considered responsible for the creation of UTWs in view of the mismatch in frequency of the two phenomena. The analysis allowed to estimate the velocity of the UTWs, obtaining values in good agreement with the literature. Finally, it was shown that by using the 11 most energetic POD modes, an accurate reduced-order model (ROM) is obtained, which when subtracted from the instantaneous velocity fields allows the visualisation of the small-scale structures present in the flow, such as the upstream travelling waves (UTWs) and the vortex shedding in the separated area near the trailing edge. The second mode was, instead, associated with an asymmetrical behaviour of the separated area and of the shear layer and displays a main peak at 320 Hz, being double the main buffet cycle frequency. The first and the third modes have a main frequency peak at 160 Hz and are well representing the separated area and the shock oscillation. It is found that the first three most energetic modes capture around 65 % of the total fluctuating kinetic energy. Proper Orthogonal Decomposition (POD) was applied to the PIV data to extract the main modes connected with buffet. A spectral analysis showed that the shock oscillation occurs with a dominant contribution at 160 Hz (St = 0.07, in good agreement with the literature) and between 25 and 55 % of the chord of the airfoil. The general behaviour of the buffet cycle was characterised with short-exposure schlieren visualisation and phase-averaged PIV measurements. ![]() 5 ∘, using schlieren and particle image velocimetry (PIV). (TU Delft Aerodynamics)Ībstract: Transonic buffet behaviour of the supercritical airfoil OAT15A was investigated experimentally at flow conditions Ma= 0.7 and α= 3. Experimental investigation of the transonic buffet cycle on a supercritical airfoil ![]()
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