# Very High Mach Number & Density - Flow over an Airfoil

Member

Hello,

I am running a simulation for the flow over an airfoil using CFX. I made it a 2D simulation by extruding the mesh by one cell, of thickness 20mm to be approximately equal to the smallest edge length of the mesh. I also tried a large extrusion of 100mm. The airfoil is around 2m long with units in mm, and the fluid domain is substantially bigger - the inlet circle diameter is 14m, length approx. 21m.

Mesh has 267336 nodes, 133396 elements.

I wanted to simulate the wing section under cruise conditions, and so I set an inlet BC at the inlet curved face with Cart. Vel. Components, where U = FreestreamVelocity = 140m/s, V = W = 0. The reference pressure was set for ISA 25,000ft - which is 37600Pa, and the Static Temp at inlet = 238K. The symmetry sides, as well as the top and bottom walls were set as symmetry planes, and the outlet as outlet of 0 Relative Pressure. I also attempted openings and free slip walls. I am solving using Air Ideal Gas, Total Energy, SST Turbulence Model with High Resolution Advection Scheme, First Order Turbulence. I have also tried to set the max fluid timescale to 0.15s - which is about equal to the residence time of the fluid (21m / 150m/s) - but this made convergence worse.

When I run the simulation, it tends to converge however the imbalances remain at around 20 (!) for some momentums. I get very fast flow - Mach numbers of up to 5, and extremely high pressures (the order of 1E8). The temperature is as I set until of course it hits one of the several shocks, however the density is also extremely high - from a minimum of 900kg/m^3 to 9000kg/m^3, and as such the mass flow is also very high.
Can anyone explain why the density is being set so high despite my boundary conditions should be running at a density of about 0.55kg/m^3?

• Forum Coordinator
edited April 13

Please post the questions in appropriate category. Moving this question to other category to get better response.

moving to fluid dynamics category.

• Member
edited April 16

My apologies, however I believed this issue to be a problem with my set up not actual fluid dynamics which is why I posted it there.

Any ideas about how to tackle the issue?