“…In this study, the BL events are investigated using the spectrogram plots for the hot-film sensors. Similar investigations were previously done for interpreting the pressure transducers data for the intake analysis by Soltani and co-workers [22]. The idea behind the spectrogram is to apply FT to a windowed part of the signal with a finite duration instead of applying the entire signal.…”
Section: Resultsmentioning
confidence: 80%
“…Where, Np is the number of discrete points in the finite signal array, n f and n A are the 4is given by [22] as:…”
Transitional boundary layer over a pitching airfoil at low Reynolds number (Re = 2.7×10 5) is experimentally investigated through the space-frequency and time-frequency analyses of hot-film signals. Boundary layer events are visualized based on the spacefrequency and time-frequency plots. The precursor phenomena for turbulent as well as fully separated flows are presented based on the time-frequency analysis. A new technique based on the time-frequency analysis of hot-film signals is presented to measure the transition onset as well as the relaminarization locations. This technique is based on the analysis of highfrequency disturbances of the measured data. Special attention is focused on the spatial/temporal progression of the transition onset and the relaminarization points, compared to the static values, for different oscillation frequencies and amplitudes. Investigations are performed prior to, within and beyond the static stall angle of attack conditions. The results obtained by the new technique will be discussed and compared with the observations from the previous investigators.
“…In this study, the BL events are investigated using the spectrogram plots for the hot-film sensors. Similar investigations were previously done for interpreting the pressure transducers data for the intake analysis by Soltani and co-workers [22]. The idea behind the spectrogram is to apply FT to a windowed part of the signal with a finite duration instead of applying the entire signal.…”
Section: Resultsmentioning
confidence: 80%
“…Where, Np is the number of discrete points in the finite signal array, n f and n A are the 4is given by [22] as:…”
Transitional boundary layer over a pitching airfoil at low Reynolds number (Re = 2.7×10 5) is experimentally investigated through the space-frequency and time-frequency analyses of hot-film signals. Boundary layer events are visualized based on the spacefrequency and time-frequency plots. The precursor phenomena for turbulent as well as fully separated flows are presented based on the time-frequency analysis. A new technique based on the time-frequency analysis of hot-film signals is presented to measure the transition onset as well as the relaminarization locations. This technique is based on the analysis of highfrequency disturbances of the measured data. Special attention is focused on the spatial/temporal progression of the transition onset and the relaminarization points, compared to the static values, for different oscillation frequencies and amplitudes. Investigations are performed prior to, within and beyond the static stall angle of attack conditions. The results obtained by the new technique will be discussed and compared with the observations from the previous investigators.
“…Soltani et al. 79 studied effects of the bleed location on the buzz phenomenon in a mixed compression axisymmetric intake. They applied a slot bleed over the cone surface upstream of the throat at three different positions (Figure 34).…”
Section: Effects Of the Bleed On Buzz Phenomenonmentioning
confidence: 99%
“…79 Figure 35.Shadowgraph pictures of buzz semi-cycle for one bleed position and different free stream Mach numbers and back pressures. 79 …”
Section: Effects Of the Bleed On Buzz Phenomenonmentioning
The paper summarizes recent developments in boundary layer suction for high-speed air intakes. Bleed has been efficiently used in supersonic and hypersonic intakes for three primary reasons: to improve the performance of the intake, to reduce the starting Mach number of the intake, and to postpone the onset of buzz oscillations. A bleed system has many characteristics such as the bleed entrance and exit areas, bleed entrance slant angle and position, and bleed type (slot or porous and ram-scoop or flush). Each of these parameters has significant impacts on the intake performance and stability that have been reviewed in this study. In addition, the effectiveness of other flow control methods has been compared with the bleed method.
“…The bleeding air in the boundary layer forced the airflow to deflect outwards, generating a series of compression waves which eventually affected the incident shock and promoted the inlet starting. Similar techniques can also be found in [8][9][10][11][12][13] . Yuan presented a reverse suction method to analyze its influence on the self-starting ability [14,15] .…”
To enhance the starting ability was one of the most serious issues in air propulsion system. In the present work, an adaptive slot control method was proposed to expand the working range of hypersonic inlets to a lower Mach number with weak losses, which was beneficial for engineering applications. Simulation results indicated that the starting Mach number can be decreased from 3.2 to 3.0 with five parallel slots at a width of 4mm. The flow inside the slot channel was self-driven due to the pressure gradient across of the separation shock. In case that the inlet was restart, the slot channel flow would be strongly suppressed.
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