• Journal of the Korean Society of Propulsion Engineers
• /
• v.21 no.2
• /
• pp.83-93
• /
• 2017

A numerical analysis is made of the fluid flow and heat transfer characteristics in the corrugated structure that traps the spent air in the corrugations between impinging jets to reduce crossflow effects on downstream jets in the array. All computations are performed by considering three-dimensional, steady state, and incompressible flow by using the ANSYS-CFX 15.0 code. Averaged jet Reynolds number is 10,000. The oblique angles of impingement jets on the spanwise section are $70^{\circ}$, $80^{\circ}$, $90^{\circ}$, and the oblique angles of impingement jets on the streamwise section are $70^{\circ}$, $90^{\circ}$, $110^{\circ}$. The investigation focuses on the oblique angle influence of impinging jet array on the fluid flow and heat transfer characteristics of a corrugated structure.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.23 no.9
• /
• pp.1172-1177
• /
• 1999

Comparisons of measured turbulence properties in the unburned gas region of turbulent premixed flame stabilized by pilot flame, in cases of combusting and non-combusting flow conditions, are presented. Methane-air premixed jet at fuel equivalence ratio of 0.6 and 1.0 and Reynolds number of 7,000 was diagnosed using two-color laser velocimeter to obtain turbulence statistics. Same set of measurements was repeated at 21 locations within the unburned gas region of both combusting and non-combusting conditions. Velocity data were analyzed to evaluate the spatial distribution of turbulence properties including Reynolds stress, probability densities, joint probability densities and auto correlations. Contrary to assumptions of current theoretical models, significant influence of flame was observed in every property that was studied in the present investigation. The effective viscosity increased ten-fold when flame was on from cold flow values. The effect of mixing on joint probability as well as in turbulence intensity was suppressed by the flame. The measurements suggest that common assumptions of premixed flame model may result in sizable error in prediction of flame length and temperature distribution in near-field.

• The KSFM Journal of Fluid Machinery
• /
• v.10 no.3 s.42
• /
• pp.25-32
• /
• 2007

The present paper deals with the heat/mass transfer characteristics for the rotating impingement/effusion cooling system. By changing the size and number of injection hole, its effects on heat/mass transfer are investigated and three different injection hole cases are considered such as LH, DH and SH, respectively. Reynolds number based on the effusion hole diameter is fixed to 3,330 and two jet orientations are considered. A naphthalene sublimation method is used to obtain the heat/mass transfer coefficients on the effusion plate. The LH case shows that the local heat/mass transfer is significantly varied by the rotation. Moreover, the low and non-uniform Sh distributions occur because the impinging jet is deflected by Coriolis force. Meanwhile, for DH and SH cases, the local heat/mass transfer coefficients are enhanced significantly compared to LH case and the rotation effect decreases with increasing the jet velocity. The averaged Sh value of DH and SH case rises up to 45%, 85% than that of LH case. However, the uniformity of heat/mass transfer deteriorates due to the steep variation of heat/mass transfer.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.32 no.4
• /
• pp.283-289
• /
• 2008

An experimental investigation was conducted to investigate the heat/mass transfer for impingement/effusion cooling system with inclined jet. Jets with inclined angle of 60 are applied to impingement/effusion cooling. At the jet Reynolds number of 10,000, the experiments were carried out for blowing ratios ranging from 0.0 to 1.5. The local heat/mass transfer coefficients on the effusion plate are measured using a naphthalene sublimation method. The result indicates that the inclined jet causes the non-uniform and low heat/mass transfer compared to the vertical jet. At stagnation region, the peak position is shifted from the geometrical center of injection hole due to Coanda effect and its level is higher than that of vertical jet due to increase in turbulence intensity by steep velocity gradient near the stagnation region. Further, the secondary peak region disappears because the interaction between adjacent wall jets weakens. When the initial crossflow occurs, the distorted heat/mass transfer pattern appears. As the blowing ratio (crossflow rate) increases, the heat/mass transfer distributions become similar to those of the vertical jet. This is because the effect of crossflow is dominant compared to that of inclined jet under high blowing ratio $(M{\geq}1.0)$. At low blowing ratio $(M{\leq}0.5)$, averaged Sh value is 10% lower than that of vertical jet, whereas its value at high blowing ratio $(M{\geq}1.0)$ is similar to that of vertical jet.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.35 no.12
• /
• pp.1059-1066
• /
• 2007

An experimental study has been conducted to investigate the flow separation control effects of a blowing jet on an elliptic airfoil at a Reynolds number of 7.84×105 based on the chord length. A blowing jet was obtained by pressing a plenum inside the airfoil and ejecting flow out of a thin jet slot that located in leading edge or trailing edge. The experimental results have shown that the blowing jet had an effect of suppressing the flow separation, resulting in the higher suction pressure distribution and higher normal force. The increase in Cn was more pronounced at higher incidence, whereas the effectiveness of the blowing jet reduced at lower incidences. The leading edge pulsating blowing with 90° was the most effective in controlling the flow separation than other types of blowing jet configuration tested in this research. Moreover, when the pulsating blowing was applied, the stall angle was postponed about 2°-3°. The continuous and pulsating blowing jet is a direct and effective flow separation control for improving the aerodynamic characteristics and performances of airfoil.

• The KSFM Journal of Fluid Machinery
• /
• v.11 no.6
• /
• pp.24-30
• /
• 2008

In order to enhance the heat/mass transfer, a turbulator has been installed at the exit of injection hole for the impingement/effusion cooling system. The local heat/mass transfer coefficients have been obtained by a naphthalene sublimation method. Experiments have been carried out at the fixed jet Reynolds number of 10,000. Two turbulators with different diameter have been used in the current study. The result presents that the turbulator leads to the increase in flow mixing and jet velocity, consequently enhancing the heat/mass transfer at a stagnation region. Further, the stagnation region is divided into four small areas with peak value. In the existence of initial crossflow, the stagnation regions move downstream and low heat/mass transfer regions are formed regardless of the installation of turbulator. However, the increased jet velocity by turbulator reduces the crossflow effect against the jet, resulting in decrease of low heat/mass transfer regions. Compared to the case without turbulator, the installation of turbulator yields $5{\sim}10%$ augmentation in averaged Sh value.

• Journal of Mechanical Science and Technology
• /
• v.15 no.5
• /
• pp.646-655
• /
• 2001

This paper reports the effects of nozzle exit boundary layer swirl on the instability modes of underexpanded supersonic jets emerging from plane rectangular nozzles. The effects of boundary layer swirl at the nozzle exit on thrust and mixing of supersonic rectangular jets are also considered. The previous study was performed with a 30°boundary layer swirl (S=0.41) in a plane rectangular nozzle exit. At this study, a 45°boundary layer swirl (S=1.0) is applied in a plane rectangular nozzle exit. A three-dimensional unsteady compressible Reynolds-Averaged Navier-Stokes code with Baldwin-Lomax and Chiens $\kappa$-$\xi$ two-equation turbulence models was used for numerical simulation. A shock adaptive grid system was applied to enhance shock resolution. The nozzle aspect ratio used in this study was 5.0, and the fully-expanded jet Mach number was 1.526. The \"flapping\" and \"pumping\" oscillations were observed in the jets small dimension at frequencies of about 3,900Hz and 7,800Hz, respectively. In the jets large dimension, \"spanwise\" oscillations at the same frequency as the small dimensions \"flapping\" oscillations were captured. As reported before with a 30°nozzle exit boundary layer swirl, the induction of 45°swirl to the nozzle exit boundary layer also strongly enhances jet mixing with the reduction of thrust by 10%.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.23 no.2
• /
• pp.175-184
• /
• 1999

A theoretical study on the turbulent round jet diffusion flame impinging on the wall was carried out to predict the characteristics and structure of Impinging jet flame and heat transfer to the wall. Finite chemistry via Arrhenius equation and eddy dissipation model was adopted as a combustion model, and the Favre averaging and $k-{\varepsilon}$ model were Introduced In the theoretical modeling. The SIMPLE algorithm was applied to the calculation. All the transport properties were considered as the variable depending on the temperature and composition. For the parametric study, the distance from nozzle to impinging wall and Reynolds number at nozzle exit were chosen 88 the major parameters. As the results of the present study, the characteristics of flow fields, the distributions of main variables and each chemical species and the flame shapes were obtained. The heat transfer rate from the flame to the wall and the effective heating area were calculated to investigate the Influences of the major parameters on the heat transfer characteristics.

• Journal of computational fluids engineering
• /
• v.18 no.2
• /
• pp.49-55
• /
• 2013

The goal of the research is to evaluate the open source code of OpenFOAM for the use of nuclear plant flow simulation objectively. Of the various incompressible flow solvers, simpleFoam, pimpelFoam are then tested under three validated cases (backward facing step, flow over circular cylinder and turbulent round jet flow). For the evaluation of steady state incompressible laminar flow simulation, low reynolds number of backward facing step flow was solved by simpleFoam. The resultant of the reattached lengths turned out to be similar with the other experimental and simulation results. For transient flow simulation, flow over circular cylinder and turbulent round jet flow were solved by pimpleFoam. The simulation accuracy was evaluated by comparing the resultant flow patterns with the description of the characteristics of the flow over the circular cylinder. The quantitative accuracy was evaluated for no more than 85% by comparing it to the decaying constants of the turbulent round jet velocity.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.22 no.7
• /
• pp.1013-1021
• /
• 1998

Various vortical structures are investigated by using three kinds of flow visualization methods in branch pipe flows. There are two typical flow patterns when a jet from the branch pipe with various angles is injected to the main pipe cross flow. The velocity range of cross flow of the main pipe is 0.2 m/s ~ 1.2 m/s and the corresponding Reynolds number, R$_{p}$ is of the range 1.5 * 10$^{3}$ ~ 9.02 * 10$^{3}$. The velocity ratio(R), jet velocity/cross flow velocity, is chosen from 1.3 to 4. The subsequent behavior and development of the ring vortices which are created at the jet boundary mainly depend on the velocity ratio. An empirical relation for the shedding frequency of the ring vortices is derived. It is also found that there are two different vortex shedding mechanism in the mixing of two fluid streams.s.