Thanks everyone for the comments.
As rb1957 pointed out, the internal wing is certainly impractical as the main source of lift for an aircraft, due to dead weight of surfaces that don’t generate lift.
The remark of btrueblood that “the idea isn't too nuts” is also important, because the pressure drop over the blown bottom surface is a valid physical phenomenon. Checked out the “Blackburn Buccaneer” and the blown flaps on Wikipedia, but they mention only one reason for blowing air over the surface, namely to reduce airflow separation.
The full description of the patent of our concern US Patent # 4,568,042 with more figures can be found at the middle of page:
. Let’s skip the other two articles above this patent for now, because those indeed contain some “verbiage that are at odds with physics” as IRstuff mentioned. The patent doesn’t claim that the internal wing as a passive system would generate thrust. The thrust and the compressed air blown over the bottom surface of the internal wing are provided by the jet engine. The brave claim that “This arrangement of airfoils reduces drag, enhances lift and thrust output” is in the article at the top of page referring to a different wing structure (triple airfoils). Let’s ignore these articles for now for better focus.
Nevertheless, even if the invention is not practical as an aircraft wing, and even though the inventor’s understanding of fluid dynamics is lacking, the basic idea may be still useful for other applications. The ultimate answers could be obtained by building and testing the structure in real life which is out of question for now. The second best, to perform a CFD analysis is under consideration, but before doing so, it makes sense to ask CFD expert opinion. With sufficient experience a CFD expert can assess fairly well the pressures, forces and torques at least qualitatively even prior to running the simulation. I don’t have this level of CFD experience and expertise, so best to ask those who have it.
Let me define more clearly what I am interested in. Let’s approach the structure of interest step by step.
1.) First we have high velocity air (or other fluid) blown over a curved surface resembling an airfoil. Due to Ventury effect there will be a reduced pressure area above the surface which generates lift. In this setup the upper wall of the duct is either missing or is very far away from the examined bottom. I suppose that this far we are correct.
2.) In the second step let’s modify the setup by introducing the upper wall of the duct, and move it towards the bottom decreasing the gap. As the gap decreases the pressure difference between the bottom surface of the top wall and the upper surface of the curved bottom wall will decrease, i.e. the lift will decrease. Let’s find an optimum distance which will not require an impractically large duct, but still yield a significant lift.
3.) In the third step let’s extend the length of the duct to be much longer than the effective curved blown surface which generates lift. We could imagine a theoretically infinitely long duct allowing the injected air to escape through holes on the side walls at a long distance from the injection. Another option is to make a toroid duct having the inlet and outlet connected. In this case the injected air could be extracted at a point 180 degrees from the injector on the sides of the duct.
Here comes the big question:
a) do we still have a lift on the duct?
b) do we have any torque on the duct?
Or generally at what step of our imaginary experiment do we loose the lifting force and/or torque on the duct if it is lost? What will cause the counter force/ counter torque that would cancel the lift and torque measured in the first step?
Perhaps I should have posted this thread in a section specialized for CFD analysis, but hope the experts will find it here as well.
