An apparatus includes a gas turbine engine flow device having an inner member and a surrounding member. The inner member has a first coefficient of thermal expansion; and the surrounding member at least partially surrounds the inner member and has a second coefficient of thermal expansion that is different from the first coefficient of thermal expansion. The surrounding member includes at least two walls that form a variable flow gap therebetween. The inner member is oriented relative to the at least two walls of the surrounding member such that, based on the difference in the first and second coefficients of thermal expansion, the inner member expands relatively greater than the surrounding member or the surrounding member expands relatively greater than the inner member, according to a temperature change to correspondingly enlarge or reduce the size of the variable flow gap between the at least two walls.