The flight process of hypersonic vehicles involves complex flow interactions, such as boundary layer transition and shock-wave/boundary-layer interactions, making velocity measurement within the boundary layer crucial for understanding aerodynamic characteristics. Femtosecond Laser Electronic Excitation Tagging (FLEET) offers significant advantages over traditional Molecular Tagging Velocimetry (MTV) by measuring hypersonic flows without the need for tracer particles. However, measuring velocity within the boundary layer remains challenging due to near-wall effects and flow disturbances. This study investigates the applicability of FLEET in hypersonic boundary layer flows, aiming to enhance understanding of boundary layer characteristics and provide data for numerical simulations. The JF10 wind tunnel generates high-temperature and high-pressure gases by detonating a hydrogen-oxygen mixture, producing a shockwave that compresses nitrogen test gas. The gas is then expanded through a nozzle to create a hypersonic flow field. A femtosecond laser focuses near the surface of a blunt-cone model, and an intensified ICCD camera captures the measurements. Velocity profiles were obtained under Ma=8.9 inflow conditions, considering factors like femtosecond filament imaging resolution. The results show that FLEET is effective for velocity measurement in the hypersonic boundary layer, with fitting coefficients exceeding 99.2%. The measurement uncertainty was determined to be 12.4%. The results validate FLEET as a feasible technique for velocity measurements in hypersonic boundary layer flows, and future research will integrate it with other laser diagnostic techniques for improved accuracy.
Plasma properties are diagnosed in parallel-plane electrodes under 1-15 kPa within input power of 0-25 W by coupling Optical Emission Spectroscopy (OES) and Planar Laser-induced fluorescence (PLIF). Electron excitation temperature (Te), electron density (Ne) are obtained based on the intensities and broadenings of atomic and ionic spectral lines of argon. The spatial resolution of Te and Ne are measured by a high-precision setup based on fiber. At the gas pressure of 1 kPa, Te reaches maximum of 8.745×103 K while the peak of Ne appears in 15 kPa, is 3.237×1016 cm-3 . Besides, spatial distribution of 1s5 metastable atoms (ArM) with transition scheme 4s( 2P0 3/2)2 -4p ( P (2P01/2)1-4s(2P03/2)1 are revealed by PLIF, as a complementary of plasma properties. The number density of ArM also shows a larger number density in 15 kPa. Combined with OES, Te, Ne and number of ArM are higher around the surface of anode within discharge area. The current experimental results are demonstration of optimal plasma state under different external parameters and validation of relevant discharge models
The model combustor of aircraft engine under fuel-lean condition is characterized by planar laser-induced fluorescence (PLIF) technique. By imaging the fluorescence from OH and CH2O simultaneously under various operation points, the transient structures of the reaction zone and preheat zone have been investigated. By the application of proper orthogonal decomposition (POD) and extended POD (EPOD) methods to the OH PLIF and CH2O PLIF data, the main dynamics modes of the swirling flame are extracted, as well as the CH2O PLIF signal distribution for each POD mode. The experimental results indicate that as the thermal power of the combustor increases, the time-averaged structure and dynamics modes experience notable transitions. At relatively high flow rate, local extinction occurs and unburnt fuel emerges in the external recirculation zone (ERZ).
Instantaneous measurement of flame spatial structure has been long desired for complicated combustion condition (gas turbine, ramjet et.). Three dimensional computed tomography of chemiluminescence (3D-CTC) is a potential testing technology for its simplicity, low cost, high temporal and spatial resolution. In most former studies, multi-lens and multi-CCD are used to capture projects from different view angles. In order to improve adaptability, only one CCD was utilized to build 3D-CTC system combined with customized fiber-based endoscopes (FBEs). It makes this technique more economic and simple. Validate experiments were made using 10 small CH4 diffusion flame arranging in a ring structure. Based on one instantaneous image, computed tomography can be conducted using Algebraic Reconstruction Technique (ART) algorithm. The reconstructed results, including the flame number, ring shape of the flames, the inner and outer diameter of ring, all well match the physical structure. It indicates that 3D combustion chemiluminescence could be well reconstructed using single camera.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.