The present invention pertains to a flow conditioner for displacing and mixing fluid flow to minimize the effects of thermal gradients on the accuracy of a transit time ultrasonic flowmeter and defines an envelope in a cross sectional direction in a pipe having a first ramp adapted to be disposed in the pipe and extending from the outside of the envelope inward toward the center of the pipe in a downstream direction with respect to the fluid flow and forming an angle between 0° and 90° relative to the pipe's inner surface. The conditioner has a second ramp adapted to be disposed in the pipe and in juxtaposition with the first ramp, the second ramp extending from the outside of the envelope inward toward the center of the pipe in an upstream direction with respect to the fluid flow and forming an angle between 0° and 90° relative to the pipe's inner surface. An apparatus for determining fluid flow in a pipe having ultrasonic transducer sites. A method for determining fluid flow in a pipe. A method for affecting fluid flow in a pipe.