Low noise turbine for geared turbofan engine

A method of operating an aircraft system including an aircraft and a gas turbine engine coupled to the aircraft, the gas turbine engine including a propulsor section including a propulsor, a gear reduction, a compressor section that drives air from the propulsor along a core flowpath, the compressor section including a first compressor and a second compressor, and a turbine section including a first turbine and a second turbine, the method comprising:

• driving the propulsor;
• driving the first compressor;
• driving the second compressor by the first turbine, wherein the first compressor includes a first plurality of stages, the second compressor includes a second plurality of stages, and the second turbine includes a greater number of stages than the first turbine;
• driving an input to the gear reduction between the propulsor and the second turbine, the gear reduction including an epicycle gear train having a gear reduction ratio of greater than 2.5:1, and the gear reduction receiving an input from the second turbine such that the propulsor turns at a lower speed than the second turbine;
• wherein the second turbine includes a number of turbine blades in each of a plurality of rows of the second turbine;
• and
• wherein the step of driving the input to the gear reduction includes operating the second turbine blades at least some of the time at a rotational speed, the number of turbine blades and the rotational speed being such that the following formula holds true for at least one row of the plurality of rows of the second turbine:
• 5500 Hz≤(number of blades×speed)/60 sec≤10000 Hz, wherein the rotational speed is an approach speed in revolutions per minute taken at an approach certification point of the aircraft as defined in Part 36 of the Federal Airworthiness Regulations, and wherein the gas turbine engine is rated to produce 15,000 pounds of thrust or more.