Depending on the model you bought, the vents may be designed for a certain riding position.
I have an HJC CL-15 (which I like…basic, but fits me well), and I’ve noticed that while riding in an upright position (like on a standard or a cruiser), there’s little difference in airflow with the vents open or closed. Around town, I do as Munch suggests and crack the visor…makes a world of difference.
But if riding in a more areodynamic position (tucked in, head forward), I can definitely feel the air flowing into the top vents.
Makes sense, as the CL-15 is designed as a sport helmet, for a sportbike riding position.