- OVERVIEW
The drag coefficient is a dimensionless value that quantifies the resistance that a body has in a fluid medium. LM RQ - 150 Sentinel is an unmanned aircraft that resembles its profile to a peregrine falcon. Its aerodynamic profile allows it to reach up to a speed of 950 km / h. There is little information on this aircraft because it is used for special operations of CIA, but this project has the measurements of one of the prototypes. Width of 10 meters, length of 2.5 meters, and a projected area 3.5 m2 approximately.
´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´
- PROJECT GOALS
The goals of this project are to calculate the drag coefficient in an enclosure too large to prevent the influence of the walls in the flow interaction. The test velocity is 950 km/h or 264 m/s. The drag coefficient will be compared with other geometries like a sphere, streamlined body, and streamlined half-body, the drag coefficient of these geometries are know.
´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´´
- GEOMETRY
The simulation was made with a preexisting CAD. The geometry was built in Siemens Solid Edge, there are some images here. Width of 10 meters, Length of 2.5 meters and maximum high of 0.5 meters.
- MESHES
A automatic hex-dominant mesh was created. The fluid domain around the drone is meshed to simulate a wind tunnel. There’re two refinements, a region refinement apply to a cartesian box that describes a near zone the Dron and a surface refinement on the principal body (aircraft). In this mesh was used fineness moderate and was allowed automatic boundary layers.
´´´´´´´´
- SIMULATIONS
For an aerodynamic analysis, a steady-state, incompressible fluid flow analysis type is employed along with a K-Omega-SST turbulence model. The analysis is carried out on 16 cores and takes nearly 40 minutes.
The convergence graph can be seen below:
The main goal of this project is to obtain the drag coefficient of the drone. This value can be observed in the graph, where at the beginning it has fluctuations but as the solution converges, the value stabilizes.
We can even see the forces generated by the pressure on the aircraft. The main forces affecting the fuselage are those directed on the X axis.
- RESULTS AND CONCLUSIONS
Post-processing for this case is performed on ParaView, here with some tools like volume extraction, slices and stream tracer. A drag coefficient value of 0.022 was obtained. This is much smaller than those shown in the initial geometries. It can be said that the aerodynamics of the LM RQ-150 Sentinel Drone is ideal and that is why such high efficiency is achieved.
Pressure Contours:
A post-processing could also be done in the SimScale viewer, in the first image the slice and stream tracer represent the velocity and the solid color of the aircraft represents the pressure.
In the second image, the slice represents the kinematic viscosity variation and the solid color on the drone continues to show the pressure profile.
SimScale Post-processing:
