Computational Fluid Dynamics Projects
Aerospike Nozzle Flowfield Simulation
The work presented here was developed through the course of a capstone project in 2015. The goal was to develop a tool to design Aerospike or plug nozzles and to integrate an Aerospike test article to an open jet facilty to capture cold flow schlieren images of the flowfield.
The image shown below features contours of Mach number from a simulation of an Aerospike nozzle operating at an altitude of 9 km from a chamber pressure of 20 bar.
The video shown here captures the initial startup of the operation of the Aerospke nozzle using a transient analysis in Ansys Fluent.
Stay tuned for more on the simulation and schlieren setup!
Identification of Shock Location in a C-D Nozzle using Analytical and Numerical Methods
The location and downstream properties of the shock can be determined using an iterative procedure, which involves assuming the location of the shock, determining the local area ratio and upstream Mach number.
Shock location based on simulation results
The normal shock tables are used to determine the flow properties after the shock and the nozzle area ratio is used to determine the flow properties at the exit of the nozzle.
If the pressure at the exit matches the imposed back pressure then the location of the shock is accurate, however if Pexit>Pb, the shock location is aft of the guessed location and fore of the guessed location for Pe<Pb. The procedure is repeated until convergence is reached for shock location.
The nozzle is symmetric about the centerline and therefore only the half nozzle was modeled with the symmetry boundary condition used at the axis. The 2D density based solver was used with the density set according to the ideal gas equation. Pressure inlet boundary condition was imposed at the inlet of the nozzle with the gauge pressure set to Pr=2 MPa. Pressure outlet boundary condition was used at the nozzle exit with the Static pressure set to the required Pb. The CFL number was set to 0.9 which from experience was determined to be ideal for supersonic internal flow simulations.
Convergent-Divergent Nozzle Simulation
In this project the flow through a convergent divergent nozzle is solved analytically for a nozzle, designed to operate ideally at an altitude of 5km. The non-isentropic solution is calculated for a range of back pressures. The analytical solution is then compared to numerical results obtained using commercial CFD code ANSYS Fluent.
Contours of Mach number
The nozzle is symmetric about the centerline and therefore only the half nozzle was modeled with the symmetry boundary condition used at the axis.
The nozzle geometry is created in ANSYS Modeller and meshed using the meshing tool. Alternatively, simple geometries like a 2d nozzle can be created in GAMBIT and exported to fluent directly.
The advantage of using Design Modeler is that any new changes made upstream can easily be updated in all associated components. A coarse mesh was used initially and subsequently meshes with increasing degrees of fineness were used until the solution was reasonably grid independent. The mesh used consists of 1000 quadrilateral cells encompassing the convergent and divergent sections of the nozzle.
The 2D density based solver was used with the density set according to the ideal gas equation. Pressure inlet boundary condition was imposed at the inlet of the nozzle with the gauge pressure set to Pr=2 MPa.
Pressure outlet boundary condition was used at the nozzle exit with the Static pressure set to the required Pb. The CFL number was set to 0.9 which from experience was determined to be ideal for supersonic internal flow simulations.