Delta Wing-Shaped Upper Jaw as a Control Surface to Stabilize Rorqual Whales During Lunge-Feeding

Abstract

During lunge feeding, rorquals depress their lower jaw to fill the buccal pouch, which can produce a downward pitch on the body from a drag force below the center of mass. It is hypothesized that without flippers the raised upper jaw could produce a counteracting lift to trim the body. Upper jaws of the blue whale and humpback whale have triangular shapes that resemble delta wings. Such wings generate lift without stalling at high angles of attack. To test whether the upper jaw is acting like a delta wing, planform shapes of jaws were tested with multiaxis force transducer in a flow tank at angles of attack. These 2-dimensional models performed like delta wings without stalling. A CFD model of an inflated buccal pouch indicated that pouch drag could be modeled as a flat plate. Comparison of flume and CFD data, on the other hand, showed pouch lift as more dependent on its degree of streamlining. Three-dimensional models of whale bodies with the lower jaw angled down at 90^o and the upper jaw angled at 0^o, 15^o, and 30^o were tested in a flow tank. Without the flippers, increasing the angle of the raised upper jaw acted as a delta wing that produces most of the lift needed to negate downward pitching due to the drag of the depressed lower jaw and inflated buccal pouch.