An Experimental and CFD Comparison of Water and Air Based Swirling Flow of Gas Turbine

Foad Vashahi,Sangho Lee,Jeekeun Lee 한국추진공학회 2016 한국추진공학회 학술대회논문집 Vol.2016 No.5

A 2D PIV experiment was carried out on the confined swirling flow and compared with simulation results. Simulations were performed via Star CCM+ commercial software. LES WALE method of air and water was used to investigate the effect of working fluid on the swirling flow field. A second comparison was done to study the gravitational effects on the swirling flow. Velocity analyses were performed by extracting the mean velocity data and FFT analysis was conducted on the instantaneous flow field of axial and pressure distribution. In general, good agreements were obtained via experimental data while interestingly the air simulation showed relatively higher performance in terms of predicting the asymmetric behavior of the flow. Energy cascade was studied on two different points which indicated a similar tendency between air and water with a slight shift of 0.1 Strouhal number in terms of dominant frequencies.

STEADY SIGNLE AND TWO-PHASE FLOW RANS SIMULATION OF PRESSURE SWIRL NOZZLE

( Foad Vashahi ),( Shahnaz Rezaei ),( Jeekeun Lee ) 한국액체미립화학회 2017 한국액체미립화학회 학술강연회 논문집 Vol.2017 No.-

A combined experimental and CFD study on a high pressure swirl nozzle with agricultural application is presented. The swirling flow is generated with the assist of inner vanes at injection pressure of 15 bar. The spray pattern is captured with high speed camera FastCam Photron SA-X2 and then is correlated with the flow swirl number measured from CFD code Star ccm+ version 11.04. In this particular nozzle, the volume of swirl chamber is adjustable to the end of changing spray pattern from hollow cone at minimum volume and full cone at its maximum. The formation of air core at the discharge orifice of pressure swirl nozzles is widely accepted. Its existence results in formation of hollow cone spray with a fine atomization. Thus, it is essential to apply two-phase flow scheme to simulate the nozzle behavior. However, these schemes are expensive and require heavy computational time. Also, simulation of single phase is by far easier to converge than that of two-phase flow. Thus, single and two-phase flow steady RANS simulations were performed and the results are compared to give insight to whether a single phase simulation suffices the required accuracy. Two-phase flow simulations were perfumed applying VOF scheme and results were validated via the experimentally achieved spray angle. The internal structure is then elaborated in single and two-phase flow and data were compared. In general, the negative volume of axial velocity developed inside the swirling chamber played an important role to achieve a wider hollow cone or narrower full cone spray pattern. In addition, the swirl decay was identified as the main parameter affecting the spray angle. Comparison of two types of simulations also revealed deficiencies in applying single phase condition.

An experimental and LES comparison of water- and air-based swirling flow test rigs in vertical and horizontal configurations

Foad Vashahi,백병준,이지근 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.7

A 2D PIV experiment was carried out on the confined swirling flow and compared with simulation results. Simulations were performed using Star CCM+ commercial software. The LES WALE method of air and water was used to investigate the effect of working fluid on the swirling flow field. A second comparison was conducted to study the gravitational effects on the swirling flow. Velocity analyses were performed by extracting the mean velocity data, and FFT analysis was conducted on the instantaneous flow field of axial and pressure distribution. In general, good agreements were obtained using the experimental data; interestingly, the air simulation showed relatively higher performance in terms of predicting the asymmetric behavior of the flow. Energy cascade was studied at two different points, which indicated a similar tendency between air and water, with a slight shift of 0.1 Strouhal number in terms of dominant frequencies. The discrepancy of the CRZ and CTRZ formation was found to be of minor degree due to changes in the working fluid or the gravitational effect. Thus, a conclusion was made regarding whether applying water instead of air or altering the vertical test rigs affects the structure of the flow.

Time-Resolved and Instantons Flow Field of Multi-Passage Swirler; An LES Study

( Foad Vashahi ),( Jeekeun Lee ) 한국액체미립화학회 2018 한국액체미립화학회 학술강연회 논문집 Vol.2018 No.-

This current research describes time-resolved interaction of shear layers in triple swirler configuration with the aid of LES simulation. In order to reduce the number of grid points and the consequent simulation time, the LES simulation is performed on region from the exit of the swirler to outlet. To ensure that such approach is valid, three preliminary RANS simulations were performed and compared with the LES results as is detailed below. For the RANS simulations, the Realizable k-ε model was used to close the Navier-Stokes equation and all the simulations are performed in nonreacting condition with air as working fluid and no-slip wall boundary condition. Polyhedral grids were used where for the first simulations a basic refinement was done at the swirler and its exit. The grids are refined via a field function, with respect to the Taylor micro-scale to resolve the small scale structures within the flow field. With such approach the total cell count was decreased from 3,009,987 to 1,815,316 cells. Comparison with the averaged experimental results indicated that implementation of such method is valid. It was found that the tangential velocity component clearly separates the counter-rotating shear layer formed from the axial and radial swirlers with two emerging flows and negative sign. The turbulence activity due to tangential velocity is higher than the other two and in addition to the interaction point of the shear layers, depicts a relatively high region of turbulence activity immediately after the swirler at the outer edge of the outer shear layer. This region contains small axial velocity component and shows a weak recirculation zone due to the high velocity gradient. The instantaneous flow field showed that vortexes are initiated at the edges of the shear layer for both the central axial swirlers and outer radial one due to the development of Kelvin- Helmholtz instabilities. These instabilities appear due to the shear generated between two adjacent high and low velocity flow. From the vorticity contours downstream, two type of vortex can be found. One is the consequence of the outer shear layer instabilities dealing with the ambient flow or Kelvin-Helmholtz instabilities and then the vortices generated due to mixing of the shear layers. Type 1 vortex leads to a local recirculation zone while the second type is characterized by high vorticity gradient due to the local zero velocity region. Due to the local zero velocity region resultant from two opposing shear layers, the flow travels around the zero velocity region and results in a much lower vorticity and strong local flow acceleration.

A preliminary investigation of the design parameters of an air induction nozzle

Foad Vashahi,Sothea Ra,최용,이지근 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.7

In the present study, an experimental study on design parameters of an air induction nozzle was performed. These nozzles are capable of producing large size droplets, including microbubbles, which in turn results in high drift reduction. A magnified 2D version of an air induction nozzle was designed and manufactured. The manufactured geometries have the ability to be disassembled easily, thus several geometrical parameters are replaced sequentially. The effects of a venturi throat, air orifices and discharge orifice diameters along with the length of the mixing chamber are analyzed. Analysis of the parameters revealed their strength of prediction on the air liquid ratio and the nozzle performance.

Parametric Study on the Swirling Flow Field of a Counter Rotating Swirler

Foad Vashahi,Sangho Lee,Jeekeun Lee 한국추진공학회 2016 한국추진공학회 학술대회논문집 Vol.2016 No.12

A numerical study using commercial software Star CCM+ version 11.04 was performed to study the effect of geometrical parameters such as chamber shape and vane geometry on the swirling flow field. Investigation was performed on a rectangular shaped model combustor chamber. RANS realizable k-ε was used and overall results showed that the chamber shape mainly affects the corner recirculation regions while the vane geometry directly affects the central recirculation zone.

A Numerical Study on the Thermal and Strain Characteristics of EGR Cooler

Foad Vashahi,Myungjae Lee,Jintaek Kim,Daesuk Kim,Byung Joon Baek 보안공학연구지원센터 2014 International Journal of Control and Automation Vol.7 No.7

Flow Analysis of an Axial Counter-rotating Swirler in a Model Gas Turbine Combustor

Foad Vashahi,Sangho Lee,Jeekeun Lee 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11

This paper reports the PIV measurement of swirling flow in a confined rectangular-shaped model combustion chamber. Flow behavior near the walls is discussed, as are other important swirling flow features such as the appearance of CRZ and CTRZ. Analyses were performed via commercial software STAR-CCM+ version 9.0. The LES dynamic Smagorinsky subgrid scale, realizable k-ε model, and k-ω SST detached eddy version were used as simulation tools. Three different test filters of 1.0, 2.2, and 3.0 were applied to the LES to identify improvements in accuracy. Finally, the best turbulence models are compared to experimental data.

A study for frequency variation along an injected fluid stream inside gas turbine combustors

Mohamed Y. Hashim,Foad Vashahi,Jeekeun Lee 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.11

In this study, numerical calculations acquired to advance toward the optimization of the fuel injection and fluidic stability inside gas turbine combustor. These calculations were performed under unsteady-state condition by using k-ε turbulence model as it has been the most foretelling scheme for modeling swirling flow inside gas turbine combustors. Swirl flow has been employed to the combustor with Methane (CH4) as the primary fuel. CH4 was injected at different inlet flow rates with constant air injection. Four planes were selected to yield an additional comprehension of the vortex breakdown characteristics with different values of frequency. The results presented here are a small and representative sample of the total. Oscillation of the flow of CH4 lead up to acceleration in the free-field of the radial pressure gradient. The pressure gradient changed to the axial direction which provides the vortex breakdown bubble and reverses the flow behavior. The stagnation point relocated due to the change in the state of vortex breakdown and the structure of the swirling flow changed.

Effect of Design Parameters on the Air-Liquid Ratio of an Agricultural Air-Induction Nozzle

Reza Alidoost Dafsasri,Foad Vashahi,Jeekeun Lee(이지근) 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.11

Drift and rebound of pesticide droplets issuing from agricultural nozzles has always been a main source of soil and water contamination in the farms. Air induction nozzles significantly improve agricultural spray through applying air bubbles into liquid drops and generating large size droplets to resist the wind and bounce. This study aims to investigating the effect of geometrical parameters of air induction nozzle on the spray performance and droplets characteristics. A domestic patented air induction nozzle was designed with variation of geometries for this study. Experimental approach employed laser diagnostic devices to measure and analyze the size of both air and liquid phase. The air to liquid ratio was measured using liquid and gas flowmeters, spray structure was captured by using high speed shadowgraphy visualization system and the droplet size was characterized by laser diffraction method and microscopic photography. The analyzed results revealed that some geometrical parameters have clear trend on the spray stabilization and characteristics where some other found to be essential for further study.