So what does the banner in the background say?
The banner says "热烈庆祝某型机FADS风洞试验模型系统研制成功", which translates as "celebrating the successful development of FADS wind tunnel test model for a certain aircraft".
FADS likely refers to
, basically using openings in an aircraft's fuselage – usually in the form of a large air data probe mounted on the nose – to arrive at its speed, angle of attack, and so on. The probe resembles a giant pitot tube that pokes way out ahead of the aircraft and directly into the airstream, and it's usually used during an aircraft's development phase. We've seen this on all kinds of prototype aircraft before, such as the
,
,
,
, and so on.
So this particular model of a stealth bomber design was put through the wind tunnel to obtain the expected air data, which could then be used to compare with data obtained from the FADS probe on an actual prototype
if this particular design ever makes it to the prototype stage.