The phrase 'a flow of people' is both correct and usable in written English. You can use it to describe a large number of people moving in the same direction, like a river of people. For example, "As the parade began, a flow of people lined the streets, cheering and waving flags.".
Outside the station, a flow of people was heading toward the down escalator.
The Socialist president said it was in both countries' interests to ensure a flow of people.
You see a flow of people coming in to buy drugs.
"It is the demand that draws a flow of people and a dark underground sex-trafficking industry".
"There was a flow of interested people coming out of that connection".
Another inspired idea: renting space on the third floor to Wilhelmina Models, guaranteeing a flow of gorgeous people through the lobby.
When I first started going I was always lost in there, doubling back upstream like a salmon against a determined flow of people, making the mistake of stopping to chat with friends coming towards me in our opposing undulating drifts.
Ludwig does not simply clarify my doubts with English writing, it enlightens my writing with new possibilities
Simone Ivan Conte
Software Engineer at Adobe, UK