Computational Fluid Dynamics: Supersonic ANSYS Simulation - Assignment Example

Computational Fluid Dynamics: Supersonic ANSYS Simulation Student Name Year Table of Contents 1.Introduction 3 Theory 6 2.Methods 7 3.Results 9 Velocity 9 Pressure 9 Temperature 9 1.The EES results 9 Comparison 10 4.Discussion 10 5.Conclusions 11 6.References 11 Lee, H. (2009). Finite Element Simulations with ANSYS Workbench 16. SDC: Springer. 11 1. Introduction Computational fluid dynamics (CFD) is becoming one of the most sought after skills in both small and large industries. According to Pozrikidis (2009), effective simulation helps reduce cost of design implementations by over 75%. A system analysis software company, ANSYS Inc. is one such a company that is a global in production, training and hence use of CFD. ANSYS CFX is one such software that is extensively applied in analysis of fluids. CFD is important in design on many accounts. Blazek (2005) says, CFD analysis applications are critical in ensuring the success of design and development phases of industrial production. They include, but not limited to internal and external fluid flows, gas or liquid flow with heat transfer, real gases, time dependent flow, heat transfer, transonic/subsonic/supersonic regimes, turbulent/laminar flows, compressible gas and conjugate heat transfer. CFD analysis is complex and needs vast experience and knowledge in thermal and fluid dynamics. Some of the analysis services include the thermal hydraulic analysis, heat transfer analysis structural fluid interaction, industrial fluid dynamic analysis and dynamic mesh analysis. For this particular experiment, CFD is applied in analysis of a supersonic wind tunnel air flowing from a hot reservoir (9000C) to a low temperature test section (400C) and at pressure 9 atmospheres via throat. CFD is particularly important/most reliable simulator for this kind of problem because of because it is used to obtain both the qualitative and quantitative analyses of the fluid study. With this tool, the boundary conditions can be determined. This makes ANSYS the most reliable in carrying out the CFD in our particular case. For a fluid under pressure (the 9 atms)/ compressible fluid dynamics, its speed of motion is compared with that of sound. The comparison is expressed in terms of ratio of the local flow-speed, u, divided by the local speed of sound, a. This is referred to as the Mach number, M expressed as below This number is used in categorizing the compressible flows into different Mach number regimes. To make the Mach number useful, it can be viewed as being directly proportional to the ratio of the Kinetic to the internal energy of the molecules (). If there is no losses involved, then the Mach number is referred to as the Isentropic Mach number. It refers to the ideal Mach number one would get without the losses and walls without friction. In this particular case, these two form the assumptions of the study. With the Isentropic state in mind, and the pressure conditions, the isentropic flow relations Mach number can be computed using the formula As the speed of motion increases beyond speed of sound, the fluid/air Mach number is greater than 1 M>1. This happens with supersonic flow. In this case, the density changes faster than the velocity changes by a factor that is equal to M squared. i.e Mach number squared. According to (), for a supersonic speed, the Mach number range is given as shown below. The Mach number, if given, can therefore be used to compute speed of flow. The table below summarizes the relationship between regime, Mach and speed. From the above descriptions, it can be concluded that CFD uses is a numerical method of analysis of fluid dynamics. It is always important, especially with simulations to carry out a test using a secondary/ standard method. The Engineering Equation-Solver (EES) is the most appropriate software used to verify/compare with simulations from another program. Theory Control volume equation. From Oosthuizen (2013) book “Introduction to compressible fluid flow”, for a given elemental mass dm that flows through an inlet or outlet port of a control volume, with an area A, volume dv, length dx and with an average steady velocity V, as follows According to () an ideal Comprehensible flow can be expressible equations Differential analysis and CFD According to Mulley (2004), for any Control volume (CV), under the conservation of momentum, the differential equation under the given velocity, V, time, t, and density p, the CFD differential equation is given by: 2. Methods This is a supersonic wind tunnel airflow experiment. In this experiment, a supersonic wind tunnel air flows from a large reservoir of 900oC and pressure 9 atm via throat to a rest section. During the testing, the thermometer reading remained almost constant at 40oC. In this experiment, based on the control volume discussed in the theory section, the equations were applied in finding the velocity of the motion. For this particular simulation, the rate of change of mass was 0.5kg/s. In the analysis of this nature, assumptions were made. The assumptions made include: 1. The motion was isentropic 2. There was no heat losses 3. There was no friction on the wall of the surface In this particular experiment, under the given mass flow rate of 0.5kg/s, the aim of this experiment is to determine the throat air temperature, throat air speed and the test section Mach number. In order to work this out effectively, the CFD analysis used ANSYS CFX simulation module. In order to verify the simulation results of the CFX, the EES was used to verify and validate the results. ANSYS simulation is more relevant since it gives the real picture of how the fluid will flow and gives a real time change as the conditions are adjusted and is therefore the most preferred option for any fluid dynamics simulations (Huei-Huang Lee, 2015). However, the results of ANSYS should always meet the scientific standards. This is measured by computing the factors using the standard engineering equations solver (EES) software which is the most reliable engineering tool for engineering equations (Blazek, 2005). The CFC experimental procedure used involved the geometry generation. This is the first step towards defining the path of fluid flow. In this experiment, for the purpose of CFD analysis given the throat structure, an elliptic 3-D geometry was adopted. In CFD analysis, the fluid flow is then computed by first generating grids which aid the conservation of the laws of physics. This process is called meshing in the ANSYS. Meshing and the solution protocols on the CFC were followed appropriately in accordance with the differential equation method of the elliptic scheme. EES was used to analytically solve the algebraic equations posed in the above sections. The CFC results and those of the EES were recorded as shown in the section below. 3. Results The geometry of the system from ANSYS Design Modeler is as shown below Following the computational equations above and applying them in the simulator, the Mach number at the test section was determined to be: Velocity The velocity in the tunnel varied in according to the position in the tunnel. The velocity was determined to be The variation of velocity with the position of fluid in the tunnel was as shown below. Plots of velocity, Pressure The pressure flow plot was as given in the flow chat below. Temperature The throat temperature was as given below. The flow plot. 1. The EES results The EES results for the Mach number, throat temperature and velocity were as shown below. Throat temperature Throat Temperature= Tab= 3530C Speed of air from ees computation U=791.2m/s Mach number The Mach number gives M=1.572 as shown above Comparison The comparison shows a greater similarity between the results of the two analytical systems. Both the speed, Mach number and the throat temperature and speed are closely similar to that of the ANSYS simulation 4. Discussion From this Experimental comparison between the ANSYS Design Modeler and the EES software, it can be concluded that the ability of the ANSYS to model complex can be relied upon. Its ease of use can be adopted in giving a wholistic view of the design in a reliable way. This would be most preferred way because it may require less engineering knowledge compared to the EES which may not be very suitable to new learners. Its presentation of the of the results and model design can as well be relied on. In both the cases, as shown by the speed of air and the Mach number computed, they are all a confirmation of supersonic flow as described at the beginning. 5. Conclusions Both the analytical and numerical results, from ANSYS Fluent and EES respectively, imply that the numerical solution using ANSYS is reliable for model design. As such, ANSYS can be reliably used to simulate a situation for proper controls before the production. 6. References Blazek, J. (2005.). Computational fluid dynamics. Mulley, R. (2004). Flow of industrial fluids. Boca Raton, Fla.: CRC Press. Oosthuizen, P. (2013). Introduction to compressible fluid flow. Pozrikidis, C. (2009). Fluid dynamics. New York: Springer. Lee, H. (2009). Finite Element Simulations with ANSYS Workbench 16. SDC: Springer. Read More