Control of plume interference effects on axisymmetric afterbodies

Plume interference effects on the axisymmetric flowfields around powered missiles are investigated using computational techniques. The study is mainly to understand the physics of the plume-induced shock and separation particularly at high plume to exit pressure ratios with and without shock-turbulent boundary layer control methods

Starting transient simulation of a vacuum ejector-diffuser system under Chevron effects

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.The vacuum ejector-diffuser system has been widely used in many applications such as refrigeration systems, high altitude test facilities and fluid transportation devices. In the present study, the starting transient flows of supersonic vacuum ejector-diffuser system, and its performance characteristics were simulated and analyzed by numerical methods. Newly designed chevron lobes were installed at the inlet of the primary stream of the vacuum ejector-diffuser system for the purpose of the performance improvement. A CFD method based on transient scheme has been applied to simulate the equilibrium flows and flow dynamics behavior of the secondary chamber. Primary numerical analysis results show that the chevrons get a positive effect on the vacuum ejector performance: less starting time and secondary chamber equilibrium pressure are found in chevron transient flow, compared with the convergent nozzle. The flow characteristics inside the ejector system are discussed using pressure history, vortices behavior, transient flow pattern and Reynolds stress distributions.dc201

A study on the unsteady aerodynamics of projectiles in overtaking blast flow fields

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.A projectile that passes through a shock wave experiences drastic changes in the aerodynamic forces. These sudden changes in the forces are attributed to the wave structures produced by the projectile-shock wave interaction. This sort of unsteady interaction normally takes place in the near filed of ballistic ranges, SILO injections, retro-rocket firings, etc. A computational study using a moving grid method is performed to analyze the effect of the projectile-shock wave interaction. Cylindrical and conical projectiles have been employed to study such interactions. It is found that the projectile configurations hardly affect its total aerodynamic characteristics when it overtakes a blast wave. However, it is noticed that the projectile configurations do affect the unsteady flow structures and hence the drag coefficient for the conical projectile shows considerable variation from that of the cylindrical projectile. The projectile aerodynamic characteristics, when it interacts with the secondary shock wave are analyzed. It is also observed that the change in the characteristics of the secondary shock wave during the interaction is different for different projectile configurations. Viscous simulations were also carried out to investigate the effect of viscosity in the flow field. It is observed that the viscosity hardly affects the projectile aerodynamic characteristics but it alters the shock structures of the unsteady flow fields.dc201

Numerical analysis of mixing guide vane effects on performance of the supersonic ejector-diffuser system

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.Supersonic ejector-diffuser system makes use of primary stream with high speed and high pressure to propel the secondary stream through pure shear action. It has many advantages over other fluid machinery such as no moving parts and no direct mechanical energy input. That's why ejector-diffuser system has been used in many engineering industrial applications such as air propulsion and ejector refrigeration. The ejector-diffuser system also can be considered as the most important device of the solar seawater desalination. Generally speaking, the flow field in the ejector-diffuser system is very difficult to be predicted due to the complicated turbulent mixing, compressibility effects and even flow unsteadiness. Many works have been done in the past years to achieve a higher efficiency and improve the performance of the ejector system, but not yet satisfactory, compared with that of other fluid machinery. Considering the complexity and difficulty on the researching, how to enhance the performance of ejector-diffuser system effectively became a significant task. In the present study, several mixing guide vanes were installed at the inlet of the secondary stream of the ejector-diffuser system for the purpose of the performance improvement. The present study aim is to lessen the negative effects on the secondary stream and get a higher level in both pressure recovery and entrainment ratio. A CFD method based on Fluent has been applied to simulate the supersonic flows and shock waves inside the ejector. Numerical analysis results of the mixing guide vane effects were validated with experimental data in the previous work. The comparison of ejector performance with and without the mixing guide vane was obtained and optimal position of mixing guide vane is discussed to increase the performance. The operation characteristics of the ejector system with different numbers of inlet guide vanes are analyzed in detail. The ejector-diffuser system performance is discussed in terms of the entrainment ratio, ejector efficiency, pressure recovery as well as total pressure loss.dc201

Optimization study on the contoured shock tube for needle-free drug delivery

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.An exciting alternative of the conventional drug delivery systems has been proposed in recent times named as transdermal powdered drug delivery. The idea is to deliver drug (in powdered from) into the human skin without using any external needle. Among different proposed systems the contoured shock tube (CST) system stands out. The performance of CST device is widely analyzed by different researchers. However, there is still room for improvement of it’s performance. This study aims at improving the performance of CST device by adjusting it’s geometry as well as operating condition. A significant improvement in the performance is reported after proper adjustment of different features of the device.dc201

An investigation of temperature separation phenomenon in the vortex chamber

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.The vortex chamber is a simple device with no moving parts that separates compressed gas into a high temperature region and a low temperature region. Recently, vortex chamber is being received much attention but also high industrial demand because of its structural simplicity and better performance of the temperature separation, compared with the previous vortex tubes. In the present study, both experimental and numerical analysis has been carried out to investigate the temperature separation inside a vortex chamber. Working fluid enters the chamber through four tangential inlet ports and exits through one central exit port. To investigate the temperature separation phenomenon, static pressures and temperatures at several points inside the vortex chamber were measured using highly sensitive pressure transducers and thermocouples. Data obtained from experiments was used to verify the computational results. 3-D unsteady RANS equations were considered to simulate compressible flow inside the vortex chamber. Numerical results were observed to be in good agreement with experimental ones. Many hypotheses are discussed in terms of energy transfer mechanisms and Pressure Gradient Waves (PGW) in the paper.dc201

CFD analysis of liquid stream going through the wire-screen mesh

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.Wire-screen mesh is normally used for the removal of particles from a liquid stream. Here we consider a system where fluid passes wire-screen mesh perpendicularly. The configurations of wire-screen mesh such as diameter and shape factor of wire affect the stream of fluid going through the screen. In this study, we performed a theoretical approach to the relation between wire mesh and fluid stream with computational fluid dynamics (CFD). FLUENT is used for the simulation. Head loss can be estimated by Rose equation when the stream passes through the wire-mesh (Rose 1945). The drag coefficient (CD) varies with the stream types. The other parameters depend on a specific mesh, velocity and pressure. In the experiment we used a screen of 50 mesh-size and water as a fluid. The pressure drop during water flow was determined. The average and maximum velocities of water were calculated. On the basis of these values, we derived a proportional factor between the velocity of fluid and head loss that can estimate CD.cs201

A study on characteristics of shock train inside a shock tube

Shock tubes are devices which are used in the investigation of high speed and high temperature flow of compressible gas. Inside a shock tube, the interaction between the reflected shock wave and boundary layer leads to a complex flow phenomenon. Initially a normal shock wave is formed in the shock tube which migrates toward the closed end of the tube and that in turn leads to the reflection of shock. Due to the boundary layer interaction with the reflected shock, the bifurcation of shock wave takes place. The bifurcated shock wave then approaches the contact surface and shock train is generated. Till date only a few studies have been conducted to investigate this shock train phenomenon inside the shock tube. For the present study a computational fluid dynamics (CFD) analysis has been performed on a two dimensional axi-symmetric model of a shock tube using unsteady, compressible Navier–Stokes equations. In order to investigate the detailed characteristics of shock train, parametric studies have been performed by varying different parameters such as the shock tube length, diameter, pressure ratio used inside the shock tube

Computational Analysis of the Performance Characteristics of a Supercritical CO2 Centrifugal Compressor

A centrifugal compressor working with supercritical CO 2 (S-CO 2 ) has several advantages over other supercritical and conventional compressors. S-CO 2 is as dense as the liquid CO 2 and becomes difficult to compress. Thus, during the operation, the S-CO 2 centrifugal compressor requires lesser compression work than the gaseous CO 2 . The performance of S-CO 2 compressors is highly varying with tip clearance and vanes in the diffuser. To improve the performance of the S-CO 2 centrifugal compressor, knowledge about the influence of individual components on the performance characteristics is necessary. This present study considers an S-CO 2 compressor designed with traditional engineering design tools based on ideal gas behaviour and tested by SANDIA national laboratory. Three-dimensional, steady, viscous flow through the S-CO 2 compressor was analysed with computational fluid dynamics solver based on the finite volume method. Navier-Stokes equations are solved with K- ω (SST) turbulence model at operating conditions in the supercritical regime. Performance of the impeller, the main component of the centrifugal compressor is compared with the impeller with vaneless diffuser and vaned diffuser configurations. The flow characteristics of the shrouded impeller are also studied to analyse the tip-leakage effect