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Regarding the noise issues of aircraft-grade test equipment benches and aircraft-grade hydraulic systems, the following is a detailed analysis of noise sources and noise reduction measures:
I. Noise from aircraft-grade test equipment benches
Test benches are mainly used for ground simulation of the loads and environmental conditions (vibration, force, temperature, etc.) of aircraft components (such as engines, control surfaces, landing gear) or the entire aircraft.
1. Main noise sources:
Drive unit:
Electric motors/engines: High-power electric motors (AC/DC) or driving engines themselves will generate electromagnetic noise (high-frequency howling), mechanical noise (bearings, rotor imbalance) and aerodynamic noise (cooling fan).
Hydraulic pump station: The high-pressure pump (plunger pump, gear pump) that provides power to the hydraulic actuator is the main source of noise, generating fluid pulsation noise (pressure fluctuation), mechanical noise (bearing, gear meshing) and cavitation noise (local low pressure forming bubble rupture).
Load simulator/actuator:
Large hydraulic or electric actuator cylinders under dynamic loads:
Internal fluid flow and valve switching generate fluid noise.
Piston rods, cylinders, and connecting parts generate mechanical friction and impact noise due to deformation or gaps caused by stress.
The rapid movement of the actuator cylinder generates airflow noise (the piston rod movement stirs up the air).
Structural vibration and resonance:
When subjected to dynamic loads, truss structures (steel structures, concrete foundations) vibrate, especially near their natural frequencies, where resonance occurs, radiating strong low-frequency structural noise. Loose connections can also exacerbate the noise.
Airflow noise: Large fans or blowers are used to cool drive motors, hydraulic oil radiators, or test specimens (such as simulated flight airflow). High-speed airflow generates vortex noise when passing through blades, grilles, and pipes.
Transmission system noise: meshing noise, friction noise, and unbalanced vibration noise generated by components such as gearboxes, couplings, and drive shafts when transmitting large torques.
Noise from auxiliary equipment: cooling water circulation pump, compressor, control system cabinet fan, etc.
2. Main noise reduction measures:
Source control:
Select low-noise equipment: Prioritize low-noise motors, hydraulic pumps (such as low-pulsation swashplate piston pumps), and fans (high-efficiency, low-noise blade design).
Optimize drive strategy: Implement frequency conversion control for the motor to avoid operation at resonant speed; optimize the pressure and flow control strategy of the hydraulic system to reduce unnecessary shocks and pulsations.
Optimize structural design: Increase the rigidity and damping of the test bench structure to avoid the resonant frequency falling within the main operating frequency band; optimize the connection design to reduce gaps and looseness.
Propagation path control (sound insulation):
Soundproof enclosure/room: Install a soundproof enclosure or build a soundproof room for the entire platform or main noise sources (such as hydraulic pump station, motor). Use multi-layer composite sound insulation materials (such as steel plate + damping layer + sound-absorbing layer), and ensure proper sealing of doors, windows, and pipe penetrations through walls.
Local noise barriers: Noise barriers are installed between noise sources and personnel/sensitive areas.
Propagation path control (vibration isolation):
Equipment vibration isolation: Vibration sources such as drive motors, hydraulic pump stations, and gearboxes are installed on high-quality elastic vibration isolators (such as steel spring vibration isolators, rubber vibration isolators, and airbag vibration isolators) to cut off the path of vibration transmission to the foundation structure.
Pipeline vibration isolation/damping: Hydraulic pipelines, air pipes, etc., use flexible connections (high-pressure hoses, corrugated pipes) and are fixed with elastic hangers/supports to avoid rigid connections transmitting vibration. Pipeline dampers or damping coatings can be installed on long pipelines.
Foundation vibration isolation: For particularly sensitive tests or low-frequency noise issues, the entire test bench foundation can be isolated using a "floating floor" or large vibration isolators.
Propagation path control (sound absorption):
Sound absorption treatment: High-efficiency sound-absorbing materials (such as centrifugal glass wool, rock wool, and porous sound-absorbing foam) are laid on the inner walls, ceiling, and surface of local barriers of the soundproof enclosure/room to absorb reverberation and reduce the internal sound pressure level.
Airflow noise control:
Muffler: Install a muffler at the intake and exhaust ports of the cooling fan (resistive mufflers are suitable for medium and high frequencies, while reactive mufflers are suitable for low frequencies).
Optimize duct design: Reduce bends and abrupt changes in cross-section to maintain smooth airflow and reduce vortex noise. Sound-absorbing treatment can be applied to the inner walls of the duct.
II. Aircraft-grade hydraulic system noise
The aircraft hydraulic system provides high-pressure power for the flight control system, landing gear retraction and extension, braking, thrust reversers, and other functions.
1. Main noise sources:
Hydraulic pump: It is the main source of hydraulic noise on the machine.
Flow/pressure pulsation: The inherent flow and pressure pulsation generated by the periodic suction and discharge of oil by the plunger in a plunger pump (most commonly used in aviation) is the core of fluid noise.
Mechanical noise: friction of bearings, distributor plate/cylinder block, and vibration of swashplate mechanism.
Cavitation noise: Insufficient oil suction from the pump or excessively low local pressure causes oil to vaporize and generate bubbles. These bubbles burst in the high-pressure area, producing high-frequency impact noise.
Piping system:
Fluid noise: High-pressure pulsating oil flowing at high speed in pipelines generates turbulent noise and eddy current noise. This noise is aggravated when flowing through bends, valves, and places where the pipe diameter changes.
Pipeline vibration noise: Fluid pulsation and turbulence excite pipeline vibration, especially when the excitation frequency is close to the pipeline's natural frequency, resonance occurs, generating strong noise and radiating it into the structure.
Cavitation noise: Cavitation occurs when the local flow velocity is too high or the design is improper, resulting in too low pressure.
valve:
Throttling noise: When oil passes through the valve port at high speed (such as servo valve, pressure control valve, check valve), it generates jet noise and turbulence noise, with more high-frequency components ("whistling").
Pressure shock: Rapid opening and closing of valves (especially solenoid valves) causes a sharp change in pressure, resulting in water hammer noise.
Accumulator: When absorbing pressure pulsations, the compression and expansion of gas in a gas-filled (nitrogen) accumulator will generate noise (especially at higher frequencies). The movement of the gas bladder or piston may also produce slight noise.
Actuator: When the actuator cylinder moves, the internal oil flow, friction of the seals, and friction between the piston rod and the support will generate noise, but it is usually less than that of pumps and valves.
Fuel tank: Noise is generated by the impact of returning oil on the oil surface, oil agitation, and the bursting of air bubbles. Vibration of the fuel tank structure also radiates noise.
System resonance: The entire hydraulic system (pump-pipeline-valve-load) may form a fluid-structure coupled resonant system, which may generate abnormal noise under certain operating conditions.
2. Main noise reduction measures:
Source control:
Select a low-pulsation pump: Use a pump with a special design (such as increasing the number of plungers, optimizing the distribution plate structure, and setting a pre-compression/decompression groove) to reduce the inherent flow/pressure pulsation.
Pump source filtering: Install a hydraulic filter/vibration damper near the pump outlet. Common types:
Accumulator-type vibration damper: It uses an airbag/piston accumulator to absorb pressure pulsations in a specific frequency band (the inflation pressure needs to be precisely adjusted).
Helmholtz vibration damper: Composed of a cavity and a short tube, it has a significant effect on absorbing vibrations at specific frequencies.
Resistive vibration dampers: These utilize porous materials or narrow slits to dissipate pulsating energy (effective at high frequencies).
Pipeline vibration damper: It uses a special flexible pipe (such as steel wire braided reinforced hose or hose with damping layer) to attenuate the transmission of pulsations.
Optimize valve design: Adopt low-noise valve core design (such as multi-stage throttling, anti-cavitation valve port) and optimize the internal flow channel of the valve to reduce turbulence.
Avoid cavitation:
Ensure the pump draws in sufficient oil (sufficient pipe diameter, low flow resistance, and a well-designed oil tank).
The system design avoids localized low-pressure areas.
Use hydraulic oil with good anti-cavitation properties.
Controlling valve action: Optimize the control algorithm to avoid excessively fast valve opening and closing speeds (especially for high-flow valves) and reduce water hammer impact.
Propagation path control (vibration isolation):
Pump vibration isolation: Mounting the hydraulic pump on the aircraft structure using high-quality elastic vibration isolators is one of the most critical measures, which can effectively reduce pump vibration and noise transmission.
Pipe vibration isolation/damping:
Use appropriate flexible supports/clamps to secure the pipes and avoid rigid contact with the aircraft structure.
Wrapping/covering damping materials (such as constraint layer damping tape or damping coating) around the pipeline can significantly reduce pipeline vibration and radiated noise.
High-pressure hoses or pulsation attenuation hoses (with a special internal structure to absorb pulsation) are used in critical areas.
Optimize pipeline layout, reduce sharp bends, and avoid resonance length.
Propagation path control (sound insulation):
Local soundproof enclosure: Install lightweight soundproof enclosures (considering heat dissipation) for pumps or valve assemblies that are particularly noisy.
Sound-absorbing materials: Sound-absorbing materials are laid on the inside of the walls of the hydraulic chamber (such as the equipment chamber) to absorb the reverberation sound inside the chamber.
System design optimization:
System impedance matching: Optimize the impedance of pumps, pipelines, and loads to reduce pressure wave reflections.
Avoid resonance: Through simulation and testing, ensure that the main operating frequency of the system avoids the inherent frequency of critical structures or fluid pipelines.
Fuel tank design: Baffles are used to reduce oil return impact and air bubbles; ventilation design is optimized; fuel tank structure is reinforced to reduce radiation.
Summarize
The noise sources of the test bench are more complex and have greater power. Noise reduction focuses on soundproof enclosures, overall vibration isolation (pump station, motor, foundation), large sound absorbers, and duct noise reduction.
Noise control in aircraft hydraulic systems focuses on source suppression (low-pulse pumps, vibration dampers, valve optimization) and transmission path blocking (pump vibration isolation, pipeline damping, local sound insulation/absorption), and must strictly consider aviation constraints such as weight, space, fire protection, and heat dissipation.
Similarities: Both rely heavily on a combination of methods, including vibration isolation (isolating mechanical vibration sources), damping (suppressing structural vibration radiation), noise reduction/filtering (eliminating fluid pulsation), and optimized design (avoiding resonance and cavitation).
Effective noise reduction typically involves a combination of measures. For critical systems, detailed noise source identification, propagation path analysis, and acoustic simulation are required to develop the most cost-effective noise reduction solution. In the aerospace field, weight and space constraints make source control and efficient damping/vibration isolation technologies particularly important.
Of course, we are professionals in all of the above. Sanyuan Environment is a professional comprehensive noise environment service provider , offering you a one-stop noise control solution.