Noise suppression units are used to cut the noise coming from the exhaust of jet engines. A turbojet relies entirely on a jet exhaust to produce thrust, with little to no bypass air to muffle the sound. That makes the exhaust the dominant noise source, so installing an exhaust noise suppression device is a common and effective way to meet strict noise limits. Other engine types have different dominant noise sources (propeller noise for turboprops, rotor and mechanical noise for turboshafts, or the bypass stream in turbofans reducing core jet noise), so they are less commonly equipped with a dedicated exhaust noise suppression unit. Therefore, the turbojet is the most likely to have one.

The key idea is that engine speed is controlled by fuel flow through the fuel control or governor, and ambient air density affects how much air is available for combustion. As the aircraft climbs, air becomes thinner, supplying less mass flow for the same rotor speed. To keep the selected RPM constant, the fuel control automatically trims fuel down. If fuel weren’t reduced, the reduced air mass could allow the turbine to overspeed or run hotter, so the automatic fuel reduction keeps the target RPM steady. The pilot doesn’t need to throttle back manually, and RPM isn’t allowed to drift with altitude—the system holds the chosen speed by reducing fuel as you climb.

The main idea is that a turbine rotor blade extracts energy from the hot gas as it passes, so the gas slows down, cools, and its pressure drops as it expands doing work on the blades. As the gas expands across the blade row, it performs work on the blades, which lowers its enthalpy.With adiabatic conditions, a decrease in enthalpy means a drop in temperature, so the static temperature falls. The blade also redirects and decelerates the flow in the magnitude sense because energy is being removed to generate shaft power, so the gas velocity decreases through the passage. The pressure falls as the gas expands and loses energy to the rotor. So the description that best fits is a decrease in pressure, accompanied by decreases in temperature and velocity across the rotor blade.

In a gas turbine, pressure increases through the compressor and is at its peak right after the last compressor stage, just before the burner. The combustor adds heat but operates at essentially the same pressure as the compressor discharge, with only a small loss due to flow friction and heat addition. After combustion, the flow goes to the nozzle where it expands to ambient, so the pressure drops back toward ambient by the time it exits. Therefore, the highest overall pressure in the cycle is at the compressor discharge, just before the burner.