Asymmetric flow path topology

A flow boundary layer restart feature, comprising:

• a first surface extending inward with respect to a flow path surface of a flow path;
• and
• a second surface extending inward with respect to the flow path surface,
• wherein the first surface intersects with the second surface to from an asymmetric notch having an asymmetric convex surface curvature at the asymmetric notch, wherein the flow path surface is an outer flow path surface of the flow path and wherein the first surface is defined by a first tube of a plurality of tubes defining a heat exchanger body, and wherein the second surface is defined by a second tube of the plurality of tubes.

A flow path wall, comprising:

• an inner flow path surface;
• an outer flow path surface;
• and
• an asymmetric notch comprising a maximum flow expansion angle and a maximum flow contraction angle, each of the maximum flow expansion angle and the maximum flow contraction angle measured with respect to the outer flow path surface,
• wherein the maximum flow expansion angle and the maximum flow contraction angle are unequal,
• wherein the flow path wall defines a plurality of tubes for a flow of a first fluid within the plurality of tubes and a flow of a second fluid over the outer flow path surface, wherein each tube of the plurality of tubes is an asymmetric elliptical tube, wherein each tube of the plurality of tubes comprises a forward major semi-axis having a length a, a forward minor axis having a length b, and an aft major semi-axis having a length c, and wherein 5≥c/b>a/b>1/2.