This is called a "strake" or "chine" (Aerodynamic fan cowl strake/chine, Nacelle strake/chine).
They allow the aircraft to generate more lift at lower speeds, which entails such positive consequences as lower stall speeds, lower landing speeds, lower take-off speeds and shorter runways.
Strakes should be used if the nacelles are mounted closely under the wing of the aircraft, see also Why don't all aircraft use/need nacelle chines?. Nacelles are usually mounted like that in order to
From US Patent 20100176249: Engine Nacelle Of An Aircraft Comprising A Vortex Generator Arrangement:
With an optimal arrangement and at high angles of attack, such vortex generators, which are known as nacelle strakes or chines, generate a powerful vortex that flows over the wing, where on a slat in front of said wing it delays airflow separation until the aircraft flies at greater angles of attack.
The idea dates back to 1971 (US Patent 3744745: Liftvanes):
in operational conditions wherein high angles of attack are encountered, such as in landing or takeoff, the vanes oppose the strong upwash around the nacelle, reducing the flow separation on its upper areas, and providing a strong downwash marked by marginal trailing vortices
From R.S. Shevell. Aerodynamic Bugs: Can CFD spray them away? 1985
DC-10 wind tunnel tests showed a significant loss in maximum lift
coefficient in the flap deflected configurations, with landing slat
extension, compared to predictions. This resulted in a stall speed
increase of about 5 knots in the approach configuration. The initial
wing stall occured behind the nacelles and forward of the inboard
ailerons. The problem was traced by flow visualization techniques to the
effects of the nacelle wake at high angles of attack and the absence of
the slat in the vicinity of the nacelle pylons. The solution was
developed in the NASA Ames Research Center 12 ft. pressurized tunnel and
turned out to be a pair of strakes mounted forward on each side of the
nacelles in planes about 45 degrees above the horizontal. The final
strake shape was optimized in flight tests. The strakes are simply
large vortex generators. The vortices mix the nacelle boundary layer air
with the free stream and reduce the momentum loss in the wake. The
vortices then pass just over the upper surface of the wing, continuing
this mixing process. The counterrotating vortices also create a downwash
over the wing region unprotected by the slat, further reducing the
premature stall. The effect of the strakes is to reduce the required
takeoff and landing field lengths by about 6%, a very large effect.