• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.25 no.3
• /
• pp.182-188
• /
• 2016

This study investigates cavity flows through a guide grill above a resonator. Vortex distributions and intake flows are simulated for various shapes of the guide grill. The flows are assumed to be compressible, unsteady, and turbulent. Numerical simulations are conducted using a large eddy simulation (LES) model. To analyze the effect of the guide grill shape, three cavity lengths (0.2H, 0.6H, and 1.0H) and cavity angles ($30^{\circ}$, $45^{\circ}$ and $60^{\circ}$) are considered based on resonator height (H). The results show that the vortex generated in the resonator by cavity flow increases with cavity length. Thus, the intake flow is minimum at the smallest cavity length and angle. However, when cavity length is equal to resonator height, the intake flow decreases. The maximum intake flow occurs at a cavity angle $45^{\circ}$ at higher cavity lengths owing to the interaction between the vortex in the resonator and intake flow.

• Journal of Mechanical Science and Technology
• /
• v.20 no.8
• /
• pp.1256-1265
• /
• 2006

The supersonic flows around tandem cavities were investigated by two-dimensional and three-dimensional numerical simulations using the Reynolds-Averaged Navier-Stokes (RANS) equation with the k- ω turbulence model. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves, and the acoustic effect transmitted from wake flow to upstream. The upwind TVD scheme based on the flux vector split with van Leer's limiter was used as the numerical method. Numerical calculations were performed by the parallel processing with time discretizations carried out by the 4th-order Runge- Kutta method. The aspect ratios of cavities are 3 for the first cavity and 1 for the second cavity. The ratio of cavity interval to depth is 1. The ratio of cavity width to depth is 1 in the case of three dimensional flow. The Mach number and the Reynolds number were 1.5 and $4.5{\times}10^5$, respectively. The characteristics of the dominant frequency between two- dimensional and three-dimensional flows were compared, and the characteristics of the second cavity flow due to the first cavity flow was analyzed. Both two dimensional and three dimensional flow oscillations were in the 'shear layer mode', which is based on the feedback mechanism of Rossiter's formula. However, three dimensional flow was much less turbulent than two dimensional flow, depending on whether it could inflow and outflow laterally. The dominant frequencies of the two dimensional flow and three dimensional flows coincided with Rossiter's 2nd mode frequency. The another dominant frequency of the three dimensional flow corresponded to Rossiter's 1st mode frequency.

• Proceedings of the KSME Conference
• /
• 2002.08a
• /
• pp.743-746
• /
• 2002

Experimental investigation of the flow field of supersonic cavity is described. In this research, supersonic cavity is used in chemical laser system. For efficient laser, downstream flow after cavity need to be uniform and clear for pressure recovery system. In previous research, it's known that there's oscillation In cavity and is due to Mach number and L/D ratio. A strong recompression occurs at the after wall and the flow is visibly unsteady. Cavity flow in this research is of the open type, that is, length-to-depth ratio $L/D<10\;at\;M\;=\;3$. Experiment is done with pressure measurement by piezo-type sensor and visualization by Schlirern method. The time-dependent experimental result is compared with computation.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2006.11a
• /
• pp.363-366
• /
• 2006

The effectiveness of two passive control techniques for alleviating the pressure oscillation generated in a supersonic cavity flow is investigated numerically. The passive devices suggested in the present research include a triangular bump and a sub-cavity installed near the upstream edge of a rectangular cavity. The supersonic cavity flow characteristics are examined by using the three-dimensional, unsteady Wavier-Stokes computation based on a finite volume scheme. Large eddy simulation (LES) is carried out to properly predict the turbulent features of cavity flow. The results show that the pressure oscillation near the downstream edge dominates overall time-dependent cavity pressure variations. Such an oscillation is attenuated more considerably using the sub-cavity compared with other methods, and a larger sub-cavity leads to better control performance.

• Journal of Ocean Engineering and Technology
• /
• v.12 no.1
• /
• pp.113-119
• /
• 1998

An experimental study was carried out in a three-dimensional cubic cavity driven by 2-dimensional plane Poiseuille flow for three kinds of Reynolds number, $10^4$, 3 $\times$ $10^4$ and 5 $\times$ $10^4$ based on the cavity width and cavity inlet mean flow velcoity. Instant simultaneous velocity vectors at whole field were measured by 2-D PIV system. Laser based illumination and two-frame grey-level cross correlation algorithm are adopted. Severe unsteady flow fluctuation within the cavity are remarkable at above Re = 3 $\times$ $10^4$ Reynolds numbers and sheared mixing layer phenomena are also found at the region where inlet driving Poiseuille flow is collided with the clock-wise rotating main primary vortex at upper center area. Instant velocity profiles reveal that deformed forced vortex formation is observed throughout the separate two areas.

• Journal of Advanced Marine Engineering and Technology
• /
• v.21 no.5
• /
• pp.557-563
• /
• 1997

The unsteady flow in three-dimensional cubic cavity with narrow channel at upper region is investigated experimentally for three kinds of Reynolds number, 1*10/sup 4/, 3*10/sup 4/ and 5*10/sup 4/ based on the cavity width and cavity inlet mean flow velocity. Instant velocity vectors are obtained simultaneously at whole field by PIV(Particle Image Velocimetry). Wall pressure distributions are estimated using Poisson equation from the velocity data. Results of PIV reveal that severe unsteady flow fluctuation within the cavity are remarkable at all Reynolds numbers and sheared mixing layer phenomena are also found at the region where inlet driving flow is collided with the clock-wise rotating main primary vortex. Instant velocity profiles reveal that deformed forced vortex formation is observed throughout the entire region and spanwise kinetic energy migration is conspicuous.

• 한국전산유체공학회:학술대회논문집
• /
• 2008.03a
• /
• pp.297-301
• /
• 2008

The flight vehicles have cavities such as wheel wells and bomb bays. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves. Resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. The flow field is observed to oscillate in the "shear layer mode" with low aspect ratio. In the present study, numerical analysis was performed for cavity flows by the unsteady compressible three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Wilcox's $\kappa$-$\omega$ turbulence model. The flow field is observed to oscillate in the shear layer mode" with large aspect ratio. Based on the SPL(Sound Pressure Level) analysis of the pressure variation at the cavity trailing edge, the dominant frequency was analyzed and compared with the results of Rossiter's formul. The aero-acoustic wave analyzed with CPD(Correlation of Pressure Distribution).

• 한국전산유체공학회:학술대회논문집
• /
• 2008.10a
• /
• pp.297-301
• /
• 2008

The flight vehicles have cavities such as wheel wells and bomb bays. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves. Resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. The flow field is observed to oscillate in the "shear layer mode" with low aspect ratio. In the present study, numerical analysis was performed for cavity flows by the unsteady compressible three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Wilcox's ${\kappa}-{\varepsilon}$ turbulence model. The flow field is observed to oscillate in the "shear layer mode" with large aspect ratio. Based on the SPL(Sound Pressure Level) analysis of the pressure variation at the cavity trailing edge, the dominant frequency was analyzed and compared with the results of Rossiter's formul. The aero-acoustic wave analyzed with CPD(Correlation of Pressure Distribution).

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2008.05a
• /
• pp.329-332
• /
• 2008

Flow imbalance among the cavities was often observed in multi-cavity mold. The flow imbalance affects on the dimensions and physical properties of melded articles. First of all, the origin of flow imbalance is geometrical imbalance of delivery system. However, even the geometry of delivery system is balanced the cavity imbalance is being developed. This comes from the temperature distribution in the cross-section of runner, which is affected by the operational conditions. In this study, experimental study of flow imbalance has been conducted for various injection speeds. This study also suggests new runner design to eliminate flow imbalance in multi-cavity injection mold. Simulation and experimental results showed suggested new designed runner could eliminate or reduce flow imbalance in multi-cavity injection mold.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2007.04a
• /
• pp.295-298
• /
• 2007

The effectiveness of passive control techniques for reducing the pressure oscillation generated in a supersonic cavity flow was investigated numerically and experimentally, respectively. The control device includes a sub-cavity installed in the upstream edge of a rectangular cavity. Time-dependent supersonic cavity flow characteristics with turbulent features were examined by using the three-dimensional, mass-averaged Navier-Stokes computation based on a finite volume scheme and large eddy simulation. The results show that the pressure oscillation near the trailing edge dominates overall time-dependent cavity pressure variations. Such an oscillation can be attenuated more significantly in the presence of the sub-cavity compared with the cavity without sub-cavity, and a larger sub-cavity leads to better control performance.