Asi Bunyajitradulya

Evolution of large eddies in compressible shear layers

The evolution of large turbulent eddies has been investigated in seven supersonic shear layers with average convective Mach numbers Mc¯ ranging from 0.22 to 0.86 and with large variation in density and velocity ratios. A two-laser, single-detector planar laser-induced fluorescence technique was used to visualize the flow and its evolution. Two-dimensional pattern matching yielded the convective velocity of the eddies. For Mc¯>0.3, fast and slow modes of eddy propagation were detected in supersonic–subsonic and supersonic–supersonic combinations, respectively. An empirical model for the convective velocity is proposed. Plan views reveal coexistence of two- and three-dimensional disturbances. Interaction among eddies appears significantly suppressed. The findings have direct impact on supersonic jet noise and are very relevant to supersonic combustion.

Sensitivity to tab disturbance of the mean flow structure of nonswirling jet and swirling jet in crossflow

Sensitivity to tab disturbance of the mean flow structure of nonswirling jet in crossflow (JICF) and swirling jet in crossflow (SJICF) is investigated. For the swirling jet, the nonzero tangential velocity, nonzero circulation jet configuration is employed. The configuration allows for the development of the skewed mixing layer at each lateral edge of the jet not to be obscured and modulated by the jet cross-stream boundary layer and the associated vorticity of the opposite sign to that of the imposed swirl. In the investigation, a heated jet is used and the temperature distributions in the cross planes downstream of the jets are surveyed upto x∕rd=1, where r is the effective velocity ratio and d is the diameter of the jet exit. A single stationary tab is alternately placed at eight different azimuthal positions along the periphery of the jet exit. For both JICF and SJICF, the results show that the mean flow structure is most sensitive to tab disturbance in the region centered on the pressure-windward to ...

Non-intrusive technique for measurement of power spectra in compressible turbulence

We present exploratory tests of a new optical method which measures directly two components of the 3-D power spectrum of the refractive-index fluctuation. The method was applied to a Mach 2 turbulent shear layer. Length scales ofO.lmm to I.Omm were resolved within a shear-layer thickness ranging from 5n1m to 10mm. At lowto-moderate wavenumbers, the spectral behavior is roughly K ~ , while at higher wavenumbers it is K ~ . ~ . These spectra slopes are in agreement with prevailing theoretical predictions for anisotropic (lowwavenumber) and isotropic (high-wavenumber) turbulence. ..j

The Characteristics of Steam Bubbles in Subcooled Boiling Flow

In two-fluid modeling and three-fluid modeling, the accurate prediction of the interfacial area concentration, interfacial heat transfer and interfacial shear stress, were required. In this works, the axial profiles of void fraction, interfacial area concentration and interfacial heat transfer coefficient along the flow direction could be measured. For the steam bubbles whose diameter were less than 8mm, the interfacial area concentration and the mean bubble diameter had a correlation with void fraction despite the variation of liquid flow rate and subcooling. In case the steam bubble collapse occurred due to an irregular bubble condensation and a turbulence of liquid flow, interfacial heat transfer coefficient with the bubble collapse was about twice of that without a bubble collapse. And the interfacial heat transfer coefficient without bubble collapse showed a good agreement with the correlation proposed by Akiyama. In addition, the supposed image processing method could be applied to the present experimental condition.Copyright