• Journal of Power System Engineering
• /
• v.15 no.3
• /
• pp.38-45
• /
• 2011

The computational flow numerical analysis was introduced to predict thc turbulent characteristics in the mixing flow structure of $45^{\circ}$ impinging round jet. This analysis has been carried out through the commercial fluent software. Realizable(RLZ) k-${\varepsilon}$ was used as a turbulent model. It can be known that mean velocities analysed through RLZ k-${\varepsilon}$ turbulent model comparatively predict well the experiments and show well the elliptic shape of mixing flow structure in the Y-Z plane, but analysed turbulent kinetic energies show somewhat differently from the experiments in certain regions.

• Journal of the Korean Society of Combustion
• /
• v.12 no.2
• /
• pp.26-33
• /
• 2007

To reveal the newly found liftoff height behavior of hydrogen jet, we have experimentally studied the stabilization mechanism of turbulent, lifted jet flames in a non-premixed condition. The objectives of the present research are to report the phenomenon of a liftoff height decreasing as increasing fuel velocity, to analyse the flame structure and behavior of the lifted jet, and to explain the mechanisms of flame stability in hydrogen turbulent non-premixed jet flames. The velocity of hydrogen was varied from 100 to 300m/s and a coaxial air velocity was fixed at 16m/s with a coflow air less than 0.1m/s. For the simultaneous measurement of velocity field and reaction zone, PIV and OH PLIF technique was used with two Nd:Yag lasers and CCD cameras. As results, it has been found that the stabilization of lifted hydrogen diffusion flames is related with a turbulent intensity, which means that combustion occurs at the point where the local flow velocity is balanced with the turbulent flame propagation velocity.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.20 no.3
• /
• pp.1040-1049
• /
• 1996

The high loading combustion is accomplished by making the turbulent intensity strong and the scale small in the premixed combustor. The Da-mkoler number, which is decreased by short turbulent characteristic time or by long chemical reaction time, can make the distributed reaction flame. So we developed a doubled jet burner for high loading combustion. The doubled jet burner was designed to make the scale of the flame small by the effect of impingement and increasing shear stress with doubled jet. We investigated the turbulence characteristics of unburned mixture and visualized several flames with the typical schlieren photography. Then we studied the influence of several factors that related the scale of flame. Consequently, the doubled jet burner can make the eddy very small. And we can obtain the detail information of the flame scale through ADSF(the Average Distance between Successive Fringes) in the micro- schlieren photography. The ADSF is not a exact flame scale, but it has qualitative trend with increasing turbulent intensity. The ADSF is diminished remarkably with increasing turbulent intensity. The reason is that strong turbulent intensity makes the flame zone thick and flamelets numerous. We can confirm this fact by the signal analysis of ion currents.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.29 no.5 s.236
• /
• pp.561-567
• /
• 2005

The effect of triangular multi-tabs attached at the perimeter of jet nozzle on flow structure in the near field was investigated experimentally. A stereoscopic PIV(SPIV) system was employed to measure three orthogonal velocity components of the 3-D turbulent jet. In this study, two different types of sharp-edged jet nozzle having 4, 8 tabs were tested at the Reynolds number of Re=10,000. SPIV measurements were carried out at 5 cross-sectional planes. Six hundred instantaneous velocity fields were measured for each experimental condition and they were ensemble averaged to get spatial distributions of turbulent statistics such as mean velocity and turbulence intensity. Entrainment rate of surrounding fluid into the tabbed jets was estimated using the measured 3-D velocity field data. The strong vortex structure was induced for the jet flow with 4 tabs, increasing entrainment rate.

• Proceedings of the KSME Conference
• /
• 2000.04b
• /
• pp.479-484
• /
• 2000

A Navier-stokes based finite volume method has been developed to analyze an incompressible, steady state, turbulent wall-jet flow. The standard k-e model, the RNG ${\kappa}-{\varepsilon}$ model and their nonlinear counterparts are adopted as a closure relationship. Comparison with the experimental data shows that a linear ${\kappa}-{\varepsilon}$ model performs satisfatorily for two-dimensional wall-jet flows. However, as the flow becomes three dimensional, the linear model fails to predict the spanwise jet growth accurately and the nonlinear model needs to be adopted to capture three-dimensional flow characteristics.

• Journal of the Korean Society for Precision Engineering
• /
• v.6 no.4
• /
• pp.43-51
• /
• 1989

Free jet was investigated experimentally and numerically in range of Reynolds number from 9900 to 21000. The working fluid was air; the mean velocity components and turbulent quantities were measured by a hot-wire anemometer. In numerical computations, the governing partial differential equations of elliptic type were solved with conventional k- ${\epsilon}$ turbulence model. The measurements show that the jet increased linearly in flow direction, and that similarity for each turbulent quantity such as Reynolds shear stress, or turbulent kinetic energy was revealed in the fully developed region. The computational results show good agreements with experiments.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.24 no.2
• /
• pp.204-213
• /
• 2000

This study deals with jet impingement, which is extensively used in the process industries to achieve intense heating, cooling or drying rates and also widely employed as a test flow for turbulent models due to its complex flow configuration, on a flat plate by numerical methods. In this calculation, the finite volume method was employed to solve the Navier-stokes equation based on the non-orthogonal coordinate with non-staggered variable arrangement. To get a better understanding for the fluid flow and heat transfer characteristics of the turbulent jet impingements, $k-{\varepsilon}-{\overline{v^{'2}}}$ turbulent model was adapted and compared with the experimental data and the result of standard $k-{\varepsilon}$ turbulent model. Numerical calculations were carried out with various flow rates, nozzle to plate distances. In the case of the axisymmetric jet impingement on a flat plate, $k-{\varepsilon}-{\overline{v^{'2}}}$ turbulent model showed better agreement with the experimental data than the standard $k-{\varepsilon}$ turbulent model in the prediction of the mean velocity profiles, the turbulent velocity profiles. the turbulent shear stress and the heat transfer rate. The highest heat transfer rate can be obtained when the impingement occurs within the potential core..

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.15 no.6
• /
• pp.2160-2170
• /
• 1991

Three-dimensional turbulent structures in the near field of elliptic jet were experimentally investigated by using a three-color, three-component Laser Doppler Velocimeter. The Reynolds number based on the nozzle exit velocity and nozzle equivalent diameter(De) was about 4*10$^{4}$. The turbulent characteristics of a sharp-edged elliptic nozzle with aspect ratio of 2 were analyzed along major and minor axis at X/De=2,3,5,7 and along the centerline up to X/De=14. Quantities measured at each point with the 3-D LDV system were three orthogonal velocity components, turbulent intensity, skewness, flatness, and Reynolds shear stress. The nondimensional mean velocities coincided well with the Schlichting's empirical curve with going downstream. Elliptic jet of AR=2 had two switching points at about X/De=2 and 16. The turbulent intensity along the minor axis was distributed widely than that along the major axis. In the near field, X/De<5, the Reynolds shear stresses of the inner part of the elliptic jet had negative value, which indicated the enhancement of entrainment toward the inner part.

• 한국연소학회:학술대회논문집
• /
• 2002.06a
• /
• pp.46-51
• /
• 2002

The measurement of velocity and stain rate field has been conducted in opposed impinging jet combustion. When a smaller diameter (5mm) orifice of pre-chamber was used, previous studies had reported that the combustion phase showed a shift from weak turbulent combustion to moderate turbulent combustion in the modified Borghi Diagram. In the case with smaller orifice diameter (5mm), NOx emission was substantially reduced by a factor 1/2 while the combustion pressure remains at the same as that in the conventional combustion. Hence, in this study, the experiment setup using PIV technique was designed to identify the relation of the strain rate distribution and NOx reduction associated with moderate turbulent combustion.

• Journal of the Korean Society of Visualization
• /
• v.3 no.1
• /
• pp.71-77
• /
• 2005

Information on temporal evolution of whole velocity fields are essential for physical understanding of a complicated turbulent flow. Due to advances of high-speed imaging technique, laser and electronics, high-speed digital cameras and high-repetition pulse lasers are commercially available in nowadays. A dynamic PIV system that can measure consecutive instantaneous velocity field with 1K$\times$ 1K pixels resolution at 1 fps was developed. It consists of a high-speed CMOS camera and a high-repetition Nd:YLF pulse laser. Theoretically, it can capture velocity fields at 20 fps with a reduced spatial resolution. In order to validate its performance, the dynamic PIV system was applied to a turbulent jet of which Reynolds number is about 3000. The particle images of 1024$\times$512 pixels were captured at a sampling rate of 4 KHz. The dynamic PIV system measured successfully the temporal evolution of instantaneous velocity fields of the turbulent jet, from which spectral analysis of turbulent structure was also feasible.