Hi,
Ref #3407. Possibly, there are official descriptions of this test set-up. However, I can postulate here. There are many photo's of different Bf 109 external air intake modifications and tests. Generally, they were for GM1, or O2, or N2O injection power boost. Also, there were ongoing issues with exhaust gas ingestion and the optimum size of the scoop for different versions of the aircraft.
The dust/sand filter began with a square intake extension with louvres on Trop versions of the Bf 109 E.
For the Bf 109 F and G Trop, the sand filter became the well-known tubular item with metal mesh or louvred sides over pleated cotton filters and a double eyelid trapdoor at the front for RAM when open.
Exhaust ingestion was countered on very early DB601 engined types with a long intake trunk in the cowling, with an opening just above the first exhaust stub. However, with the Bf 109 E, the small square intake with cascades was deemed satisfactory.
These photo's seem to show an early 1941 built F-2 with the open exhaust stubs on the left cowling. The Intake scoop looks to be a larger development with the extended tube that looks to have a temperature probe fitted at the bottom. My guess is that they are testing for exhaust ingestion.
The solution to the ingestion problem on later F/G and K versions was to use a deflector lip on the extended top plate of the exhaust trough. That allowed the later, larger inlet scoops to avoid exhaust ingestion, without complications.
Eng