• Advances in aircraft and spacecraft science
• /
• v.1 no.1
• /
• pp.27-41
• /
• 2014

An active flow control technique based on "smart-tabs" is proposed to delay flow separation on a circular cylinder. The actuators are retractable and orientable multilayer piezoelectric tabs which protrude perpendicularly from the model surface. They are mounted along the spanwise direction with constant spacing. The effectiveness of the control was tested in pre-critical and in post-critical regime by evaluating the effects of several control parameters of the tabs like frequency, amplitude, height, angular position and plate incidence with respect to the local flow. Measurements of the mean static pressure distribution around the cylinder were used to estimate the pressure drag coefficient. The maximum drag reduction achieved in the pre-critical regime was of the order of 30%, whereas in the post-critical regime was about 10%, 3% of which due to active forcing. Furthermore, pressure fluctuation measurements were performed and spectral analysis indicated an almost complete suppression of the vortex shedding in active forcing conditions.

• 한국연소학회:학술대회논문집
• /
• 2000.05a
• /
• pp.117-121
• /
• 2000

We developed a general purpose program for the analysis of flows in a gas turbine combustor. The program uses non-staggered grids based on finite volume method and the cartesian velocities as primitive variables. We calculated a flow inside the C-type diffuser to check the boundary fitted coordinate. The velocity profiles at cross section agree well with experimental results. We calculated turbulent diffusion flame behind a bluff body for the combustion simulation. Simulation shows two recirculating region like experimental results. Simulated velocity, turbulent kinetic energy, temperature and concentration distribution agree well with experimental data. Finally, simulation of axisymmetric flows with swirl shows two recirculating region like experimental results.

• 한국연소학회:학술대회논문집
• /
• 2005.10a
• /
• pp.198-203
• /
• 2005

The LES-based level-set flamelet model has been applied to analyze the turbulent propane/air premixed bluff-body flame with a highly wrinkled flame fronts. The present study has been motivated to investigate the interaction between the flame front and turbulent eddies. Special emphasis is given to study the effect of G equation filtering treatment on the precise structure of turbulent premixed flames as well as the effect of sub-grid scale (SGS) eddies on the wrinkling of the flame surface. The level-set/flamelet model has been adopted to account for the effect of turbulence-flame interaction as well as to properly capture the flame front. Numerical results indicate that the present LES-based level-set flamelet approach has a capability to realistically simulate the highly non-stationary turbulent premixed flame.

• 한국연소학회:학술대회논문집
• /
• 2004.06a
• /
• pp.75-82
• /
• 2004

The conditional moment closure(CMC) model has been implemented in context with the unstructured-grid finite-volume method which efficiently handle the physically and geometrically complex turbulent reacting flows. The validation cases include a turbulent nonpremixed $CO/H_2/N_2$ Jet flame and a turbulent nonpremixed $H_2/CO$ flame stabilized on an axisymmetric bluff-body burner. In terms of mean flame field, minor species and NO formation, numerical results has the overall agreement with expermental data. The detailed discussion has been made for the turbulence-chemistry interaction and NOx formation characteristics as well as the comparative performance for CMC and flamelet model.

• 한국전산유체공학회:학술대회논문집
• /
• 2010.05a
• /
• pp.437-441
• /
• 2010

LES results of turbulent premixed combustion flows are introduced by using the dynamic sub-grid scale model based on G-equation describing the flame front propagation. The turbulent premixed combustion flows around bluff body and over backward facing step are analyzed to validate present formation. LES of swirling partially premixed combustion flame is also performed to conform the predictive capabilities of LES model and to prompt our understanding for the combustion flows over double cone swirl burner combustor by using CFD-ACE+ commercial code.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.12 no.4
• /
• pp.916-925
• /
• 1988

The Navier-Stokes equations of the vorticity-stream-function form are solved numerically for the flow past a semicircular arc for Reynolds numbers in the range 0.1

• Proceedings of the KSME Conference
• /
• 2002.08a
• /
• pp.439-442
• /
• 2002

In this study, a turbulence simulation is carried out in a suction type wind tunnel using grids, where turbulent flows with various turbulence intensity are successfully produced by the change of grid size, arrangement of grids and settling position, respectively. Response tests of rectangular cylinder models with aspect ratio of 2 and 4 are carried out in smooth flow and generated turbulent flows. Additionally, two types of fairing are considered such as right triangle and regular triangle. The effects of wind velocity fluctuations and fairing are discussed on vortex-induced oscillation.

• Journal of Mechanical Science and Technology
• /
• v.18 no.10
• /
• pp.1869-1879
• /
• 2004

The present study has numerically investigated two-dimensional flow over three circular cylinders in an equidistant side-by-side arrangement at a low Reynolds number. For the study, numerical simulations are performed, using the immersed boundary method, in the range of g* < 5 at Re= 100, where g* is the spacing between two adjacent cylinder surfaces divided by the cylinder diameter. Results show that the flow characteristics significantly depend on the gap spacing and a total of five kinds of wake patterns are observed over the range: modulation-synchronized (g* (equation omitted) 2), inphase-synchronized (g* (equation omitted) 1.5) , flip-flopping (0.3 < g* (equation omitted) 1.2) , deflected (g* (equation omitted) 0.3), and single bluff-body patterns (g* < 0.3). Moreover, the parallel and symmetric modes are also observed depending on g* in the regime of the flip-flopping pattern. The corresponding flow fields and statistics are presented to verify the observations.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.2
• /
• pp.512-518
• /
• 1994

An experimental study is made on turbulent diffusion flames stabilized by a circular cylinder in a divergence flow. In this paper, stabilization characteristics and flame structure are examined by varying the divergence angle of duct and position of a circular cylinder. The fuel used is a commercial grade gaseous propane injected by two slit of rod. It is found that the positive pressure gradient greatly influences the eddy structure behind the rod. and that two different kinds of combustion patterns exist at the blowoff limit depending on the divergent angle of duct. They are distinguished by their wake structures: one associated with Karman vortex shedding, the other without it. Also, the blowoff velocity in the former is found to be higher than in the later.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.28 no.12
• /
• pp.1616-1624
• /
• 2004

The conditional moment closure(CMC) model has been implemented in context with the unstructured-grid finite-volume method which efficiently handle the physically and geometrically complex turbulent reacting flows. The validation cases include a turbulent nonpremixed CO/$H_2$/$N_2$ Jet flame and a turbulent nonpremixed $H_2$/CO flame stabilized on an axisymmetric bluff-body burner. In terms of mean flame field, minor species and NO formation, numerical results has the overall agreement with expermental data. The detailed discussion has been made for the turbulence-chemistry interaction and NOx formation characteristics as well as the comparative performance for CMC and flamelet model.