What is this flying boat being restored at the Udvar Hazy Center?
It is a Sikorsky JRS-1 (Like terry I thought it was a PBY as well at first glance, that center wing joint is fairly unique)

From the smithsonian website you can find all the info on it here


  This amphibious seaplane is the only aircraft in the Museum that was
  at Pearl Harbor, Hawaii, on December 7, 1941. Ten JRS-1s were at the
  U.S. naval base when the Japanese attacked during World War II. The
  Navy immediately sent these unarmed utility craft to search for the
  enemy fleet. The JRS-1 (used 1937-1944) is the military version of the
  Sikorsky S-43 "Baby Clipper." On the day of the attack, the plane wore
  a very colorful paint job: silver overall, black on the bottom, green
  tail surfaces, a red band around the rear of the fuselage, and the
  diamond-shaped squadron insignia behind the cockpit on each side. A
  few days after the attack, ground crew repainted the plane blue, but
  it has weathered and the original paint is peeking through. The
  JRS-1’s current condition is due to many years of storage outside. The
  Museum intends to conserve and restore the plane. Transferred from the
  U.S. Navy, Bureau of Weapons