Experimental Study Of Supersonic Flow Research Articles

Experimental study of supersonic flow around an axisymmetric annular cavity at angles of attack

The experimental results on supersonic flow around an axisymmetric annular cavity on the cylindrical body with a nose cone are presented. In experiments, the cavity pressure was measured and the schlieren images of flow around the body were visualized. The hysteresis phenomenon due to an abrupt change in the structure of flow around the cavity was identified when the cavity length and the attack angle of the body in the supersonic flow were continuously varied.

Visualization of Supersonic Low-Noise Flow Over Surface-Mounted Two-Dimensional Prisms

An experimental study of supersonic flow over two-dimensional surface-mounted prisms is carried out in a Mach 3 low-noise wind tunnel. The noise level of this supersonic wind tunnel, defined as the root mean-square Pitot pressure fluctuation normalized by the mean Pitot pressure, can be reduced to about 0.37%. The nanotracer planar laser scattering (NPLS) technique is used to analyze the influence of the prism geometry and the oncoming flow conditions on the typical flow structures including separation and reattachment shocks. With increase in the prism height the induced shocks move upstream. At a constant streamwise length L of a prism the timeaveraged NPLS images show that the length of the downstream recirculation region increases from 0.8L to 1.2L, when the prism height H changes from 3 to 5 mm. As compared with the flow structures occurring downstream of the prisms, the upstream flow structures are more susceptible to the oncoming boundary layer and are considerably different in laminar and turbulent flows. The separation shock wave is clearly visible in turbulent flow even for the 1-mm prism, whereas in the case of laminar flow there is no a distinct shock wave upstream of this prism. At the same time, the location of the flow reattachment and the angle of the reattachment shock wave in the downstream flow remain almost the same in both two flow regimes.

Experimental study of supersonic flow over cavity with aft wall offset and cavity floor injection

Experimental studies were conducted at Mach 1.71 supersonic flow over open cavity to find the best configuration of combined passive (aft wall offset) and active methods (cavity floor injection) to optimize the noise suppression. Cavity of length to depth ratio 3 with 0%, 5% and 10% aft wall offset were analyzed with the combined effect of 2 bar, 4 bar and 6 bar injection pressures, injected from locations of 25%, 50% and 75% of cavity length from the front wall. Experimental methodology includes instantaneous schlieren visualization and unsteady pressure measurements. In all the schlieren images, the presence of shear layer and various cavity flow features are clearly visible. Suppression in tonal amplitude for increase in offset and injection pressure is observed for various injection locations. Injection location at 75% cavity length from front wall was found to provide the maximum suppression. Spectrogram plots clearly indicate the redistribution of energy among tones and broadband noises. Increase in the number of tones is observed for higher injection pressure and aft wall offset combination. Nature of acoustic wave is confirmed from correlation and coherence plot. Over All Sound Pressure Level (OASPL) and normalized mean pressure plot are used to perform comparative study for various configurations.

Amplitude and phase modulation of cavity modes in a supersonic flow

An experimental study of supersonic flow over a cavity is carried out. The study includes flow visualization and unsteady pressure measurements. From the flow visualization it is observed that the flow field is highly unsteady and that four types of waves are present in the flow field. Spectra of the unsteady pressure data display high amplitude cavity tones. The pressure data is analysed by means of the continuous wavelet transform. Wavelet analysis using the Morlet wavelet function shows that the cavity acoustic modes are both amplitude and phase modulated simultaneously in time. However it is observed that the amplitude of the modulations differs from one cavity mode to the other. The power spectral density of individual time series signals obtained from the wavelet transform indicates that the cavity modes modulate with multiple frequencies rather than at a single frequency. The dominant frequency of amplitude modulation of the cavity modes is the frequency of the dominant cavity mode. The temporal behaviour of phase modulation indicates that there exist non-linear interactions between the cavity modes.

Computational and experimental study of supersonic flow over axisymmetric cavities

Laminar and turbulent computations are presented for annular rectangular-section cavities, on a body of revolution, in a Mach 2.2 flow. Unsteady ‘open cavity flows’ result for all laminar computations for all cavity length-to-depth ratios, L/D (1.33, 10.33, 11.33 and 12.33). The turbulent computations produce ‘closed cavity flows’ for L/D of 11.33 and 12.33. Surface pressure fluctuations at the front corner of the L/D = 1.33 cavity are periodic in some cases depending on the cavity length and depth, the boundary layer at the cavity front lip and the cavity scale. The turbulent computations are supported by experimental schlieren images, obtained using a spark light source, and time-averaged surface pressure data.

Effect of aft wall slope on cavity pressure oscillations in supersonic flows

AbstractAn experimental study of supersonic flow over wall mounted cavities with different aft wall angles is carried out. Unsteady pressure measurements were made on the walls and floor of the cavity. Data analysis was performed on the experimental results using statistical methods. In the case of higher angled cavities, the presence of an upstream traveling acoustic wave could be confirmed. For lower angled cavities (60 degrees and less) where the acoustic wave could not be identified, the flow inside the cavity was more or less stable. Mode switching occurring in higher angled cavities was confirmed by spectrogram studies.

Experimental Study of Supersonic Flow Around Truncated Cones at Incidence

Results of an experimental study of supersonic flow around truncated cones with cone half-angles of 20, 30, and 40°, performed at Mach numbers M = 2, 3, and 4 within the range of angles of attack up to 20°, are presented. A relationship is established between the emergence of an internal shock wave and the character of pressure distribution along the generatrix of the truncated cone. It is shown that the known boundaries of regimes obtained for axisymmetric flow around sharp and blunt cones can be used to predict flow regimes in the vertical plane of symmetry of the truncated cone at incidence.

An experimental study of supersonic flow over a rearward facing step.

Some of the results of an experimental investigation of the flow pressure structures of a supersonic flow over a rearward facing step are presented. Included are some of the data of that part of the investigation being conducted at the Technion of Haifa, Israel. The results presented in this paper show that the pressure changes from freestream pressure to base pressure are linear functions of freestream pressure for each Mach speed and step height; the corner pressure expansion fan is not the linear Prandtl-Meyer fan; the separation (lip-shock) shock emerging from the separated shear layer may not be neglected in such flows; base pressures influence the flow upstream of the corner so that conventional considerations about the boundary layer arriving at the corner are questionable; and the Reynolds number based on the step height appears to be important. Some typical shadowgraph pictures and data studies representing the referred to flow structures are presented. Also presented is a preliminary study of the separation shock structure.