CFD analysis of UAVs using VORSTAB, FLUENT, and advanced aircraft analysis software

The University of Kansas has long been involved in the research and development of uninhabited aerial vehicles, UAVs. Currently a 1,100 lb UAV has been designed, built, and flown from the University. A major problem with the current design of these UAVs is that very little effort was put into the aerodynamics. The stability and control derivatives are critical for the flight of the vehicle, and many methods can be used to estimate them prior to flight testing. The topic of this research is using high fidelity computer software, VORSTAB and FLUENT, to determine the flying qualities of three different UAVs. These UAVs are the 1/3 scale YAK-54, the MantaHawk, and the Meridian. The results found from the high fidelity computation fluid dynamics programs were then compared to the values found from the Advance Aircraft Analysis, AAA, software. AAA is not considered to be as accurate as CFD, but is a very useful tool for design. Flight test data was also used to help determine how well each program estimated the stability and control derivative or flying qualities.;The YAK-54 results from both programs were very close to each other and also to the flight test results. The results from the other two UAVs varied largely, due to the complexity of the aircraft design. VORSTAB had a very difficult time handling the complex body of the Meridian. Its results showed the aircraft was unstable in several different modes, when this is known to not be the case after several flight tests.;From these results it was determined that VORSTAB, while a high fidelity program, has difficulty handling aircraft with complex geometry. If the aircraft is a traditional style aircraft with non-complex geometry VORSTAB will return highly accurate results that are better than AAA. The benefit of AAA is that a model can be created rather quickly and the results will typically be within an acceptable error range. A VORSTAB model can be very time consuming to make, and this can outweigh the improved results. It is rather simple to determine if the VORSTAB results are valid or not, and the input file can be easily improved to increase the accuracy of the results. It is always a smart idea to use both software programs to check the results with one another.;FLUENT was used to determine the possible downwash issue over the Meridian fuselage. This software is a widely accepted program that is known to produce very accurate results. The major problem is that it is very time consuming to make a model and requires someone with a large amount of knowledge about the software to do so. FLUENT results showed a possibility for a large boundary layer near the tail and flow separation at high angles of attack. These results are all discussed throughout the report in detail.