Low noise compressor rotor for geared turbofan engine

A method of designing a gas turbine engine comprising the steps of:

• including a turbine section having a fan turbine for driving a fan through a gear reduction, the gear reduction positioned between the fan on one side and the fan turbine on another side and having a gear reduction ratio of greater than 2.5:1;
• providing a first compressor including a plurality of blade rows;
• selecting a combination of a number of blades in at least one row of the first compressor and a rotational speed of the first compressor in operation, for producing noise frequencies that are of less concern to humans;
• said selecting step including determining the number of blades in the at least one row of the first compressor and determining a rotational speed of the first compressor in operation such that the following formula holds true for said at least one row of the first compressor:
• (said number of blades×said rotational speed)/60 sec≧5500 Hz;
• said rotational speed being an approach speed in revolutions per minute, taken at an approach certification point as defined in Part 36 of the Federal Airworthiness Regulations;
• and
• wherein a pressure ratio across the fan turbine being greater than 5, and the gas turbine engine is rated to produce 15,000 pounds of thrust or more.

A gas turbine engine comprising:

• a fan, a turbine section having a fan drive turbine, and a compressor section having a first compressor;
• a gear reduction positioned between said fan on one side and said fan drive turbine on another side and having a gear reduction ratio of greater than 2.5:1;
• said first compressor having a number of compressor blades in at least one of a plurality of rows of said first compressor, and said blades rotatable at least some of the time at a rotational speed in operation, and said number of compressor blades in said at least one row and said rotational speed being such that the following formula holds true for said at least one row of the first compressor:
• 5500 Hz≦(said number of blades×said rotational speed)/60 sec≦6000 Hz;
• said rotational speed being an approach speed in revolutions per minute, taken at an approach certification point as defined in Part 36 of the Federal Airworthiness Regulations;
• and
• wherein a pressure ratio across the fan drive turbine being greater than 5.