Local television broadcasters wanting to track down improved cash flow think they've found it in a grand central station.A television station, that is. Following a practice that has become common among companies that own multiple radio stations, television station operators are starting to move engineering and back-office functions out of the different stations that they own and into one central location that feeds video to several cities at once. Cost savings from the consolidation strategy could improve operating cash flow margins about five percentage points above industry averages, according to Ackerley Group a company that has embraced the broadcasting hub approach. But with investors waiting to see whether the promised savings really drop to the bottom line, station groups' market valuations don't yet appear to reflect centralized broadcasting's economic potential. And the centralization, which Ackerley dubs Digital CentralCasting and which others refer to by various names such as clustering or hubbing, does reflect real potential. "It's significant enough that just about every major television station group in the country is moving in that direction," says Keith Fawcett, an analyst at Merrill Lynch.