A. B. M. Toufique Hasan

Control of Transonic Flow with Non-Equilibrium Condensation around a Circular Arc Blade using Pump

Flow induced aerodynamic instability in transonic flow field is initiated by the shock-boundary layer interaction which is frequent in turbomachinery. In recent years, the effect of bump wall on the flow field around an airfoil has been investigated experimentally and as a result, it was observed that the bump wall is effective for the control of shock wave on the airfoil. In the transonic or supersonic flow field, a rapid expansion of moist air or steam gives rise to non-equilibrium condensation. In the present study, the effect of non-equilibrium condensation of moist air on the self-excited shock wave oscillation around a circular arc blade with or without a bump on the blade was investigated numerically. The results showed that the nonequilibrium condensation and bump on the blade significantly reduced the flow field unsteadiness compared to the case without the non-equilibrium condensation and without bump. Nomenclature Cp specific heat at constant pressure, J/(kg · K) chord length of the blade, mm various constants in turbulence model, turbulence model coefficient, various moments in liquid phase production equations, inviscid flux vectors, total energy per unit volume, J/m frequency, kHz viscous damping function, condensate mass fraction, turbulence source term, height of the test section, mm nucleation rate per unit volume and time, c C Cp D E, F E, / fp g H H / k turbulent kinetic energy, m/s L latent heat of condensation, J/kg M Mach number, / Molecular weight, kg/kmol p pressure, kPa pb back pressure, kPa Pk turbulence production rate, m/s Pr Prandtl number, β Condensation source term, r droplet radius, m rc critical droplet radius, m R, S viscous flux vectors, R eddy viscosity, Pa · s 91 gas constant, J/(kg · K) Re Reynolds number, R, turbulent Reynolds number, S degree of supersaturation, Corresponding author: Dr. Shigeru Matsuo Department of Mechanical Engineering, Saga University, 1, Honjo-machi, Saga-shi, Saga, 840-8502, Japan Tel: +81-952-28-8606. Fax: +81-952-28-8587. E-mail: matsuo@me.saga-u.ac.jp

Mechanical micropumps and their applications: A review

Micropump has recently become one of the major research topics especially under the field of biofluidic and microfluidic research. Based on the pioneering works in the early 1980, developments on micropumps using microfabrication technology shifted towards MEMS area around 1990. Since then, the MEMS technology has been developed to make the micropumps compatible for various biomedical applications. The developments have led to the design and fabrication of various types of micropump concepts that are suitable for carrying out particular tasks. The concepts have successfully been applied in transdermal insulin delivery, blood transportation through artificial heart, injection of glucose and drugs, for chemical and biological sensing and for electronic cooling in micro integrated circuits (μ-IC). Generally two categories of micropumps have been reported-Mechanical micropumps and Dynamic micropumps. Different micropumps are effective and suitable for different applications which can be determined by analyzin...

Analysis of viscous micropump with single rotating cylinder

This study presents the transient nature and performance of viscous micropump for low Reynolds number where flow is assumed laminar, unsteady, incompressible and two dimensional. The device consists of a cylinder placed eccentrically inside an extremely narrow channel, where channel axis is perpendicular to cylinder axis. When the cylinder rotates, it generates a net force on fluid due to unequal shear stresses on the top and bottom surfaces of the cylinder. This net force is capable of generating a net flow against a pressure gradient. The flow field inside the micro channel has been analyzed by using structured grid Finite Volume Method (FVM) based on Navier-Stokes equation. All parameters used in flow simulation are expressed in non-dimensional quantities for better understanding of flow behavior, regardless of dimensions or the fluid that is used. The effect of the channel height (S), the cylinder eccentricity (e), the Reynolds number (Re) and Pump load (P*) have been studied. Various flow patterns inside the micro pump as well as variations in flow velocity with time are obtained. Both the steady state and transient results of viscous micro pump are validated. It is found that the average velocity of fluid increases with increasing cylinder eccentricity and decreases with increasing the channel height.

A computational study on oblique shock wave-turbulent boundary layer interaction

A numerical computation of an oblique shock wave incident on a turbulent boundary layer was performed for free stream flow of air at M∞ = 2.0 and Re1 = 10.5×106u2005m−1. The oblique shock wave was generated from a 8° wedge. Reynolds averaged Navier-Stokes (RANS) simulation with k-ω SST turbulence model was first utilized for two dimensional (2D) steady case. The results were compared with the experiment at the same flow conditions. Further, to capture the unsteadiness, a 2D Large Eddy Simulation (LES) with sub-grid scale model WMLES was performed which showed the unsteady effects. The frequency of the shock oscillation was computed and was found to be comparable with that of experimental measurement.

An analysis of thrust vectoring in a supersonic nozzle using bypass mass injection

Nozzles are generally designed to produce thrust in a direction perpendicular to its exit plane. In high speed flight vehicles, rapid control of thrust direction (i.e. thrust vectoring) is an obvious requirement for high performance aerospace applications. Shock vector control is one of the efficient ways to achieve this thrust vectoring. In this present study, a bypass mass injection is used to generate shock vectoring in a planar supersonic Converging-Diverging (CD) nozzle. Injection was done by a 10mm×10mm square channel which is kept perpendicular at the diverging section of the nozzle. Investigation is carried out at Nozzle Pressure Ratio (NPR) of 2.4 which gives an overexpanded nozzle flows. The flow conditions and the size of the injection channel gives a bypass mass flow ratio of 4.9%. Reynolds-averaged Navier-Stokes (RANS) equations with k-omega SST turbulence model have been implemented through numerical computations to capture the three-dimensional steady characterstics of the flow field. Results showed a significant change in the shock structure with the fromation of recirculation zone near the bypass injection port. Consequently, a change in mass flow direction has been obtained which results a considerable thrust vectoring in a supersonic nozzle.Nozzles are generally designed to produce thrust in a direction perpendicular to its exit plane. In high speed flight vehicles, rapid control of thrust direction (i.e. thrust vectoring) is an obvious requirement for high performance aerospace applications. Shock vector control is one of the efficient ways to achieve this thrust vectoring. In this present study, a bypass mass injection is used to generate shock vectoring in a planar supersonic Converging-Diverging (CD) nozzle. Injection was done by a 10mm×10mm square channel which is kept perpendicular at the diverging section of the nozzle. Investigation is carried out at Nozzle Pressure Ratio (NPR) of 2.4 which gives an overexpanded nozzle flows. The flow conditions and the size of the injection channel gives a bypass mass flow ratio of 4.9%. Reynolds-averaged Navier-Stokes (RANS) equations with k-omega SST turbulence model have been implemented through numerical computations to capture the three-dimensional steady characterstics of the flow field. Resul...

Performance analysis of a viscous micropump with dual rotating cylinders

Micropump has many attractive features which make them potential for use in biomedical engineering and in a number of miniature technologies. In this study, the performance characteristic of a viscous micropump consisting of two counter rotating cylinders has been investigated. These cylinders are placed symmetrically at vertical position inside the micropump. To capture the flow field, the Navier-Stokes equations have been computed based on Finite Volume Method (FVM). Numerical results have been validated with available experimental data for the case of a single rotor micropump. Then the proposed micropump has been redesigned and optimized the geometric configuration using a parametric study. The flow characteristics are found qualitatively similar to those of a single rotor pump. However, it is found that the effective pumping performance of a dual rotor micropump is considerably higher for a wider range of Reynolds numbers compared to a single rotor pump.Micropump has many attractive features which make them potential for use in biomedical engineering and in a number of miniature technologies. In this study, the performance characteristic of a viscous micropump consisting of two counter rotating cylinders has been investigated. These cylinders are placed symmetrically at vertical position inside the micropump. To capture the flow field, the Navier-Stokes equations have been computed based on Finite Volume Method (FVM). Numerical results have been validated with available experimental data for the case of a single rotor micropump. Then the proposed micropump has been redesigned and optimized the geometric configuration using a parametric study. The flow characteristics are found qualitatively similar to those of a single rotor pump. However, it is found that the effective pumping performance of a dual rotor micropump is considerably higher for a wider range of Reynolds numbers compared to a single rotor pump.

Large eddy simulation of shock train phenomena in a gas dynamic flow passage

In the present study, a numerical computation of shock train phenomena inside a gas dynamic flow passage is studied. The flow passage is of rectangular cross-section with a diverging angle of 1.3°. Reynolds averaged Navier-Stokes (RANS) equations with EARSM (Explicit Algebraic Reynolds Stress Model) turbulence model are initially implemented for steady computation. These results are compared with the experiment at the same flow conditions. After that, the results from steady computation are taken as the initial conditions for the unsteady computation using Large Eddy Simulation (LES). LES with a sub grid scale (SGS) model shows an unsteady effect. Shock train structure, Mach no. distribution and separation characteristics are analyzed. The back and forth movement of shock train without any external excitations (self-excited oscillation) is well observed. The distribution of frequency of the shock train oscillation is computed and analyzed inside the gas dynamic flow passage.In the present study, a numerical computation of shock train phenomena inside a gas dynamic flow passage is studied. The flow passage is of rectangular cross-section with a diverging angle of 1.3°. Reynolds averaged Navier-Stokes (RANS) equations with EARSM (Explicit Algebraic Reynolds Stress Model) turbulence model are initially implemented for steady computation. These results are compared with the experiment at the same flow conditions. After that, the results from steady computation are taken as the initial conditions for the unsteady computation using Large Eddy Simulation (LES). LES with a sub grid scale (SGS) model shows an unsteady effect. Shock train structure, Mach no. distribution and separation characteristics are analyzed. The back and forth movement of shock train without any external excitations (self-excited oscillation) is well observed. The distribution of frequency of the shock train oscillation is computed and analyzed inside the gas dynamic flow passage.

Numerical investigation of gurney flap aerodynamics over a NACA 2412 airfoil

From the time of its invention, the Gurney flap has been successfully employed as high lift augmentation device to enhance the aerodynamic performance of modern aircraft wings. These small flaps are located perpendicularly at the suction side of an airfoil near its trailing edge. By the addition of gurney flap wake is stabilized which ensures laminar flow over the suction side and thus shifts the shock. This study investigated the aerodynamic effect of a Gurney flap on a NACA 2412 airfoil for the subsonic condition. Flap height ranges from 2% to 5% of the airfoil chord length. The investigation was evaluated at 0° to 32° angle of attack under subsonic Mach number. The numerical analysis was performed using Computational Fluid Dynamics program to predict the flow field. The analysis shows that the optimal size of the device is always below the boundary-layer thickness at the trailing edge and it tends to increase lift to drag ratio significantly. The gurney flap with 2%C height provides the best performance rather than 3, 4 and 5% Gurney flap. The investigation concludes with a suggestion that Gurney flap may lead to drag reduction in high lift regions, thus, increasing the lift-to-drag ratio before the stall.From the time of its invention, the Gurney flap has been successfully employed as high lift augmentation device to enhance the aerodynamic performance of modern aircraft wings. These small flaps are located perpendicularly at the suction side of an airfoil near its trailing edge. By the addition of gurney flap wake is stabilized which ensures laminar flow over the suction side and thus shifts the shock. This study investigated the aerodynamic effect of a Gurney flap on a NACA 2412 airfoil for the subsonic condition. Flap height ranges from 2% to 5% of the airfoil chord length. The investigation was evaluated at 0° to 32° angle of attack under subsonic Mach number. The numerical analysis was performed using Computational Fluid Dynamics program to predict the flow field. The analysis shows that the optimal size of the device is always below the boundary-layer thickness at the trailing edge and it tends to increase lift to drag ratio significantly. The gurney flap with 2%C height provides the best performanc...

Effect of flap temperature on single expansion ramp nozzle performance

The single expansion ramp nozzle (SERN) is severely overexpanded when the vehicle is at low speed, which hinders its ability to provide optimal configurations for combined cycle engines. The over-expansion leads to flow separation as a result of shock wave/boundary-layer interaction (SWBLI). Flow separation, and the presence of shocks themselves, result in performance loss in SERN, leading to reduced thrust and increased pressure losses. This study investigates the effectiveness of wall cooling in enhancing the performance of an overexpanded SERN by controlling SWBLI. Numerical simulations were carried out with the SERN flap at different temperatures, and the resulting changes in flow pattern and performance were analyzed. The results indicate significant reduction in separation size with decreasing flap temperature. In order to understand the mechanism behind this, various boundary layer properties were analyzed. Significant changes were observed in several boundary layer parameters. Two important SERN p...

Effects of cavity size on the control of transonic internal flow around a biconvex circular arc airfoil

In transonic flow conditions, self-sustained shock wave oscillation on biconvex airfoils is initiated by the complex shock wave boundary layer interaction which is frequently observed in several modern internal aeronautical applications such as inturbine cascades, compressor blades, butterfly valves, fans, nozzles, diffusers and so on. Shock wave boundary layer interaction often generates serious problems such as unsteady boundary layer separation, self-excited shock waveoscillation with large pressure fluctuations, buffeting excitations, aeroacoustic noise, nonsynchronous vibration, high cycle fatigue failure and intense drag rise. Recently, the control of the self-excited shock oscillation around an airfoil using passive control techniques is getting intense interest. Among the passive means, control using open cavity has found promising. In this study, the effect of cavity size on the control of self-sustained shock oscillation was investigated numerically. The present computations are validated with a...