• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1607-1612
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• 2004

Numerical simulations are performed to investigate the characteristics of flow past a sphere in uniform shear. The Reynolds numbers considered are Re=300, 425 and 480 based on the inlet center velocity and sphere diameter. The non-dimensional shear rate K of the inlet uniform shear is varied from 0 to 0.15. At Re=300, the head of the hairpin vortex loop always locates on the high-velocity side in uniform shear, and the flow maintains the planar symmetry. At Re=425 and 480, the irregularity in the location and strength of the hairpin vortex appearing in uniform inlet flow is much reduced in uniform shear, but the flows still keep the asymmetry for most inlet shear rates. However, in the cases of K=0.075 and 0.1 at Re=425, the flows become planar symmetric and their characteristics of the evolution of the hairpin vortex loops are different from those of asymmetric flows. A hysteresis phenomenon switching from the planar symmetry to the asymmetry (or vice versa) depending on the initial condition is also observed at Re=425.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.9
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• pp.1325-1334
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• 1998

The objectives of the present study are to develop a systematic method rather than a conventional trial-and-error method for an optimal shape design using a mathematical theory, and to apply it to engineering problems. In the present study, an optimal condition for a minimum pressure loss in a two-dimensional curved duct flow is derived and then an optimal shape of the curved duct is designed from the optimal condition. In the design procedure, one needs to solve the adjoint Navier-Stokes equations which are derived from the Navier-Stokes equations and the cost function. Therefore, a computer code of solving both the Navier-Stokes and adjoint Navier-Stokes equations together with an automatic grid generation is developed. In a curved duct flow, flow separation occurs due to an adverse pressure gradient, resulting in an additional pressure loss. Optimal shapes of a curved duct are obtained at three different Reynolds numbers of 100, 300 and 800, respectively. In the optimally shaped curved ducts, the separation region does not exist or is significantly reduced, and thus the pressure loss along the curved duct is significantly reduced.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2530-2535
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• 2008

The Visualizations of the flowfield through tube banks with in-line and staggered arrangements were investigated by PIV. Strouhal numbers, velocity vectors and velocity profiles around the cylinders with in-line and staggered arrangements were observed at the pitch ratio $P_t/D=2.0$ and Reynolds number of $Re=4.0{\times}10^3$. As the results The flow patterns through tube banks were almost a straight line in case of the in-line arrangement while it was almost 八 type in case of the staggered arrangement in the direction of the wake. The average velocity in the rear region of the tube banks with the staggered arrangement was far smaller than that with the in-line arrangement. The Strouhal number in the last rank was far smaller than that in the front ranks in both of the in-line and staggered arrangements. The wake of each cylinder changed with time and with the position of the cylinder.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.8
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• pp.401-407
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• 2017

The effect of different rib geometries such as V-shaped continuous (case A), parallel broken (case B), and V-shaped broken (case C) ribs on local heat transfer distributions and pressure drops in a divergent channel with $30^{\circ}$ inclined ribs on one wall or two walls was investigated for Reynolds numbers from 22,000 to 75,000. Top and bottom walls were insulated; two side walls were uniformly heated in the divergent channel. Heated walls were composed of 10 isolated coper sections and length-to-outlet hydraulic diameter ratio of 10. Rib height-to-outlet hydraulic diameter ratio was 0.1, and rib pitch-to-height ratio equaled 10. Results revealed that V-shaped continuous rib (case A) produced approximately 1.4 times higher average Nussselt number than in the parallel broken rib (case B), and V-shaped broken rib (case C) in the channel with two ribbed walls at Re = 54,000.

• Journal of the Korean Society of Propulsion Engineers
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• v.7 no.2
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• pp.7-14
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• 2003

Computational work using the axisymmetric, compressible, Navier-Stokes Equations is carried out to predict the discharge coefficient of mass flow through a micro-critical nozzle. Several kinds of turbulence models and wall functions are employed to validate the computational predictions. The computed results are compared with the previous experimented ones. The present computations predict the experimental discharge coefficients with a reasonable accuracy. It is found that the standard $\kappa$-$\varepsilon$turbulence model with the standard wall function gives a best prediction of the discharge coefficients. The displacement thickness of the nozzle wall boundary layer is evaluated at the nozzle throat and is well compared to a prediction obtained by an empirical equation. The resulting displacement thickness of the wall boundary layer is about 2% to 0.6% of the diameter of the nozzle throat for the Reynolds numbers of 2000 to 20000.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.3
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• pp.282-291
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• 1998

Heat transfer performance are studied for the turbulent flow of water in 3 smooth tube coils having ratios of coil to tube diameter of 16, 21 and 27, and a corrugated-coiled tube having a ratio of coil to tube diameter of 29, for Reynolds numbers from 8000 to 60000 and is also compared with the limited results available to data. The experiments are carried out for the fully developed turbulent flow of water in tube coils under the condition of uniform heat flux. This work is limited 0 tube coils of R/a between 10 and 30. The tube having a ratio of coil to tube diameter of 27 among the 3 smooth tube coils shows the best heat transfer performance. The performance of coiled tube best transfer performance. The performance of coiled tube with a similar curvature ratio is better for a corrugated-coiled tube(R/a=17) than for a smooth coiled tube(R/a=16). An empirical relation which correlates most of the data within $\pm$25% was also developed. Test result shows that the Nusselt number is found to be affected by a secondary flow due to curvature.

• Korean Chemical Engineering Research
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• v.56 no.2
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• pp.252-260
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• 2018

Energy, a critical input, is to be efficiently managed via waste heat recovery and energy reuse for the economic viability of a process industry. In particular, cement manufacture demands a huge quantum of energy, for the necessary reactions. Huge amounts of hot effluent gases are generated. Energy recovery from these waste gases is an area that is of contemporary research interest. Now, about 75% of total heat recovery takes place in the riser of the suspension pre-heater system. This article deals with the hydrodynamic and heat transfer aspects of riser typically used in the cement industry. An experimental apparatus was designed and fabricated with provision for the measurement of gas pressure and solid temperatures at different heights of the riser. The system studied was air - chalcopyrite taken in different particle sizes. Acceleration length ($L_A$) determined at different parametric levels was fitted to an empirical correlation: $L_A/d_t=4.91902(d_p/d_t)^{0.10058}(w_s/w_g)^{-0.11691}(u_g{\mu}_g/d_t^2g{\rho}_g)^{0.28574}({\rho}_p/{\rho}_g)^{0.42484}$. An empirical model was developed for Nusselt number as a function of Reynolds and Prandtl numbers using regression analysis: $Nu=0.40969(Re_p)^{0.99953}(Pr)^{0.03569}$.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.6
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• pp.155-165
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• 1998

The resistance coefficient and heat transfer performance are studied for the turbulent water flow in a smooth coiled tube having variable curvature ratios and a corrugated-coiled tube having a ratio of coil to tube diameter of 22. Experiments are carried out for the fully developed turbulent flow of water in tube coils on the uniform wall temperature condition. This work is limited to tube coils of R/a between 22 and 60 and Reynolds numbers from 13000 to 53000. The tube having a ratio of coil to tube diameter of 27 among the 3 smooth tube coils shows the best heat transfer performance. A corrugated-coiled tube(R/a=60) shows more excellent performance than a smooth coiled tub (R/a=60) at a similar curvature ratio. The friction factor f is sensitive to changes in the velocity profile caused by a temperature gradient. Allowance was made for the pressure loss in the short inlet and outlet lengths and due to the presence of the thermocouple inlet and outlet as a result of separate experimental on a straight tube. It is to be expected that the allowance at the exit will be somewhat too low because of secondary flow effects carried over from the coil.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.2
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• pp.121-130
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• 2009

An unsteady numerical simulation method for an autorotating rotor in forward flight was developed. The flapping and rotational equations of motion of autorotation are continuously integrated for given time steps, meanwhile the induced velocity field at disc plane is obtained by the dynamic inflow theory embodying the unteadiness. The transitions from arbitrary initial states to equilibrium states were simulated. Steady autorotations as numerical solutions of equations were predicted by using two sources of blade airfoil data. The simulations using airfoil data which were obtained by a two dimensional Navier-Stokes solver in terms of angles of attack and Reynolds numbers have shown good agreements with wind tunnel experimental results.

• Journal of Power System Engineering
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• v.15 no.5
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• pp.43-48
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• 2011

The article represents an experimental investigation on friction and turbulent flow characteristics of free airflow through a rectangular duct fitted with semicircular ribs of uniform height (e = 3.5 mm) on one principle wall. The aspect ratio of the rectangular duct was AR= 5 where the duct height (H) was of 30 mm. Four different rib pitches (P) of 28 mm, 35 mm, 42 mm and 49 mm were used for constant rib height to hydraulic diameter ratio (e/Dh = 0.07) and constant rib height to channel height ratio (e/H = 0.11). The experimental results show some significant effects on pressure drop as well as turbulent characteristics at various configurations among different numbers of rib arrangements varying Reynolds number in the range of 15000 to 30000. Pressure transducer and hot wire anemometer were used for data acquisition of this experiment.