Effect of Cavities in Suddenly Expanded Flow at Supersonic Mach Number

The contribution from the base drag due to the sub-atmospheric pressure is significant. It can be more than two-thirds of the net drag. There is a need to increase the base pressure and hence decrease the base drag. This research examines the effect of Mach Number on base pressure. To accomplish this objective, it controls the efficacy in an enlarged duct computed by the numerical approach using Computational Fluid Dynamics (CFD) Analysis. This experiment was carried out by considering the expansion level and the aspect cavity ratio. The computational fluid dynamics method is used to model supersonic motion with the sudden expansion, and a convergent-divergent nozzle is used. The Mach number is 1.74 for the present study, and the area ratio is 2.56. The L/D ratio varied from 2, 4, 6, 8, and 10, and the simulated nozzle pressure ratio ranged from 3 to 11. The two-dimensional planar design used commercial software from ANSYS. The airflow from a Mach 1.74 convergent-divergent axi-symmetric nozzle expanded suddenly into circular ducts of diameters 17 and 24.5 mm with and without annular rectangular cavities. The diameter of the duct is taken D=17mm and D=24.5mm. The C-D nozzle was developed and modeled in the present study: K-ε standard wall function turbulence model was used with the commercial computational fluid dynamics (CFD) and validated. The result indicates that the base pressure is impacted by the expansion level, the enlarged duct size, and the passage’s area ratio.

Application of Polyhedral Mesh for Vortex Formation Study for Simple Single Pump Sump

Meshing of domain in CFD is an important step to ensure accuracy of the solution. In the past, hexahedral or tetrahedral mesh systems were commonly used, and both have their merits and demerits. For large and complex geometry, polyhedral is another option but its accuracy is claimed to be lacking. In this paper, the use of polyhedral mesh system by past researchers are reviewed. Evaluation on the application of polyhedral mesh system for the study of the vortex formation with a simple single pump sump model is made. Validation was made through the comparison of the results from hexahedral, tetrahedral and polyhedral mesh sizes and the experimental data from published data. The polyhedral mesh system was found to perform satisfactorily and was able to match the results from the hexahedral mesh system as well as the experimental data.

Simulation Analysis of Thermal Mixing Characteristics of Fluids Flowing Through a Converging T-junction

Temperature fluctuation occurs while mixing of hot and cold fluids in a T-junction due to incomplete thermal mixing. This temperature fluctuation can produce thermal fatigue at the weld area of the T-junction. The present study aims to numerically investigate the thermal mixing characteristics of hot and cold fluids in a T-junction. The realizable k-ε turbulence model is used with natural gas as the working fluid. Temperature distribution, mixing quality, and intensity of temperature fluctuation are evaluated and compared along with the mixing outlet. The inlet temperature difference and branch to main pipe flowrate ratio have a direct influence on thermal mixing. The higher temperature difference can reduce the thermal mixing performance. Thermal mixing increases with the increase of branch to main pipe flowrate. The intensity of temperature fluctuation is found within a short distance from the intersecting point of the two inlets. With the increase of distance along with the mixing outlet, the frequency of temperature fluctuation decreases, and thermal mixing increases.

A Validation Study of the Aerodynamic Behaviour of a Wind Turbine: Three-Dimensional Rotational Case

Numerical modelling and simulation of a rotating, tapered, and twisted three-dimensional blade with turbulent inflow conditions and separating flows is a challenging case in Computational Fluid Dynamics (CFD). The numerical simulation of the fluid flow behaviour over a wind turbine blade is important for the design of efficient machines. This paper presents a numerical validation study using the experimental data collected by the National Renewable Energy Laboratory (NREL). All the simulations are performed on the sequence S of the extensive experimental sequences conducted at the NASA/Ames wind tunnel with constant RPM and variable wind speeds. The results show close agreement with the NREL UAE experimental data. The CFD model captures closely the totality of the defining quantities. The shaft torque is well-predicted pre-stall but under-predicted in the stall region. The three-dimensional flow and stall are well captured and demonstrated in this paper. Results show attached flow in the pre-stall region. The separation appears at a wind speed of 10 m/s near the blade root. For V>10m/s, the blade appears to experience a deep stall from root to tip.

Flow Behaviour Assessment of Smokey SAM Rocket Prototype

This paper presents an aerodynamic assessment on the "Smokey Sam Prototype (TRL-6) Start (X)". Initially, the rocket prototype was designed using OpenRocket open source software, where all of the user's design requirements and objectives are considered. The TRL-6 Smokey Sam Star (X) is expected to fly within 400 m with the operating Mach 0.2, as comparable to US GTR-18A. This research evaluates the aerodynamics performance of the design Smokey Sam prototype rocket using a computational fluid dynamics (CFD) approach. For instance, the CFD study assessed the flight performance and stability once launched, such as lift coefficient, drag coefficient and pitching moment. This research employs K-omega (k-ω) model to express the turbulent properties of the flow. The actual pressure distribution was compared with the conventional rocket material's exact pressure distribution to inspect the best rocket material to sustain the best strength to weight ratio at high-speed trajectory operation. Several observations were made into the modelling process, such as surrounding velocity and pressure. It is found that the flight is in stable mode since the obtained pitching moments are almost zero at all assessed speeds.

Design Optimization of Diffuser Augmented Wind Turbine

The wind turbine power decreases at low wind speed. A flanged diffuser plays a role of a device for collecting and accelerating the approaching wind, and thus the optimization of the diffuser shape presents an important way to enhance the wind turbine power. In this work, a numerical parametric study was conducted on the diffuser to obtain the initial optimum form of flanged diffuser. Then, the Simplex algorithm is used to obtain the optimal diffuser shape starting from the obtained initial shape. Finally, the obtained optimum diffuser shape is used with conventional wind turbine blade. The diffuser shape is defined by four variables: open angle, flange height, centerbody length, and flange angle. The numerical simulation of flanged diffuser is carried out using the “CFDRC package. The results indicated that, the optimum diffuser shape can be obtained using simplex algorithm which maximizes the entrance average velocity to reach 1.77 times wind speed. The power augmented by a factor about 2.76:5.26 of a selected small wind turbine using the obtained diffuser shape compared to that without diffuser.

Three Dimensional MHD Hybrid Nanofluid Flow with Rotating Stretching/Shrinking Sheet and Joule Heating

A three-dimensional hybrid nanofluid flow over a stretching/shrinking sheet is numerically studied. The hybrid nanofluid being considered in this study used water as the base fluid and mixed with two types of solid nanoparticles, namely alumina (Al2O3) and copper (Cu). The main focus of the current study is to examine the effect of magnetic field, Joule heating, and rotating sheet on the velocity, and temperature profiles. In addition, the impact of suction and stretching sheet on the variations of reduced skin friction, , and reduced heat transfer are studied as well. The fluid flow and heat transfer problem presented in this study is governed by a system of nonlinear partial differential equations (PDEs), which is then transformed into the corresponding system of high order nonlinear ordinary differential equations (ODEs) using similarity variables. The resulting system of higher order nonlinear ODEs is solved numerically using a boundary value solver known as bvp4c, which operates on the MATLAB computational platform. Results revealed that dual solutions exist for shrinking sheet while unique solutions are observed for stretching sheet with various values of Cu nanoparticles volume fraction and magnetic parameter. Dual solutions also exist for the value of the suction parameter greater than its critical point with various values of Cu nanoparticles volume fraction. Velocity profile of the hybrid nanofluid increases alongside with the value of magnetic parameter but declination was observed in the profile of and temperature, for both solutions as the value of Cu nanoparticles volume fraction increases. When the value of rotational parameter increases, both velocity and profiles increase for both solutions. This indicates that the momentum boundary layer thickness increases with increasing values of for both solutions, but thermal boundary layer thickness decreases for the first solution and increases for the second solution. Finally, an increment in the value of Eckert number causes the temperature of the hybrid nanofluid to rise as well for both first and second solutions.

Numerical Studies on Thermo-Hydraulic Characteristics of Turbulent Flow in a Tube with a Regularly Spaced Dimple on Twisted Tape

Heat transfer augmentation is an important concern due to the increase in heat management problems in thermal systems. There are many techniques for enhancement of heat transfer, by active and passive techniques. A commonly used passive technique to enhance heat transfer is by inserting twisted tapes in tubes. This work presents a numerical study on Nusselt number, friction factor, and thermal performance characteristics through a circular pipe built-in with/without dimples on twisted tape. The analysis results for a turbulent flow range of 4500≤Re≤20000 are obtained with a twist ratio of the strip is 3.0. The analysis is carried for full-length tape with constant heat flux. The governing equations are numerically solved by a finite volume method using the RNG κ–ε model. The simulation results of Nusselt number versus Reynolds number of the plain, plain twisted tape and dimple twisted tape tube with the experimental data give a variation of 4.15%, 3.89%, and 7.65%. The friction factor of the dimple twisted tape tube is 60 to 70% higher than that of the plain twisted tube at different Reynolds numbers. The thermal performance factor of the dimple twisted tape and plain twisted tape tube is 30 to 35% respectively higher than that of the plain tube. Due to thermal performance factor is above unity yields a promising heat transfer enhancement. By the present study, an optimum geometrical parameter can be selected for use in heat exchangers.

Thermal Radiation in Nanofluid Penetrable Flow Bounded with Partial Slip Condition

Thermal radiation enhances heat transfer, and it is used widely in manufacturing and materials processing applications. Thus, steady two-dimensional boundary layer flow over an exponentially porous shrinking sheet of nanofluids was considered in the influence of thermal radiation related to partial slip boundary conditions and suction. This paper aims to study the nanofluid penetrable flow over an exponentially shrinking sheet with thermal radiation and partial slip. The effects of silver (Ag) nanoparticles with two different types of base fluids named water and kerosene oil are investigated in this study. First, the governing equations and boundary conditions are transformed to a non-linear ordinary differential equation and then solved using bvp4c solver. Using Matlab software, it is found that the dual solution exists in some values from the suction parameter. Furthermore, we identified both nanoparticle volume fraction and suction parameter increase, leading to the rise in velocity profile. Moreover, the suction parameter increases both skin friction coefficient and Nusselt number increase.

Hydrodynamic Analysis of Laminar Mixed Convective Flow of Ag-TiO2-Water Hybrid Nanofluid in a Horizontal Annulus

Nanofluids occupy a large place in many fields of technology due its improved heat transfer and pressure drop characteristics. Very recently, a new type of nanofluid, known as hybrid nanofluid, which consists of a mixture of two different nanoparticles suspended in the base fluid has been found to be the most emerging heat transfer fluid. It is well also established that entrance region effect enhances heat transfer rate. The present study deals with numerical investigations of the hydrodynamic behavior of the laminar mixed convective flow of a hybrid nanofluid in the entrance region of a horizontal annulus. A thermal boundary condition of uniform heat flux at the inner wall and an adiabatic outer wall is selected. The SIMPLER numerical algorithm is adopted in the present study. The hybrid nanofluid consists of water as base fluid and Ag-TiO2 as nanoparticles. The ratio of Ag to TiO2 is maintained as 1:3. The objective of the current study is mainly to analyze the hydrodynamic behavior hybrid nanofluid in the entrance region. The investigation reveals that the effect of the secondary flow due to the buoyancy forces is more intense in the upper part of the annular cross-section. It increases throughout the cross-section until its intensity reaches a maximum and then it becomes weak far downstream. The development of axial flow and temperature field is strongly influenced by the buoyancy forces.