I have seen this part on a me 262 model kit but I don't know what it is... I've make some research on it but I find nothing! Maybe it can be radar, or a weapon? Do you know what is this? And also its function?
They are Werfer-Granate 21 rocket launchers -
The Werfer-Granate 21 rocket launcher, also known as the BR 21 (the "BR" standing for Bordrakete) in official Luftwaffe manuals, was a weapon used by the German Luftwaffe during World War II and was the first on-board rocket placed into service by the Luftwaffe, first introduced in mid 1943.
On the Me262 they were mounted one each side of the nosegear well.
Messerschmitt Me262A-1a 'Green 3' of the Geschwaderstab [headquarters unit] of JG 7 prepared to move off across the concrete surface at Brandenburg-Briest in February or early March 1945. The aircraft, finished in a relatively rare application of streaked horizontal lines, has been fitted with a pair of 21cm WGr air-to-air mortar tubes visible beneath the fuselage aft of the nose wheel. (source)