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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 the noise sources and noise reduction measures:
1. Aircraft-grade test equipment bench noise
Test benches are mainly used to simulate the loads and environmental conditions (vibration, force, temperature, etc.) of aircraft components (such as engines, control surfaces, landing gear) or the entire aircraft on the ground.
1. Main noise sources:
Drive unit:
Motor/engine: High-power motors (AC/DC) or drive engines themselves generate electromagnetic noise (high-frequency whistling), 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 (bearings, gear meshing) and cavitation noise (local low pressure forms bubbles and bursts).
Load Simulator/Actuator:
Large hydraulic or electric actuators, when applying dynamic loads:
Internal fluid flow and valve switching generate fluid noise.
Mechanical friction and impact noise are generated due to deformation of the piston rod, cylinder body and connecting parts due to stress or gap.
Rapid actuator movement produces airflow noise (the piston rod movement stirs up the air).
Structural Vibration and Resonance:
When subjected to dynamic loads, the test bench structure (steel structure, concrete foundation) will vibrate, especially when it resonates near its natural frequency, radiating strong low-frequency structure-borne 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 pieces (such as simulated flight airflow). When high-speed air flows through blades, grilles, and ducts, vortex noise is generated.
Transmission system noise: meshing noise, friction noise, and unbalanced vibration noise generated by components such as gearboxes, couplings, and drive shafts when transmitting large torque.
Auxiliary equipment noise: cooling water circulation pump, compressor, control system cabinet fan, etc.
2. Main noise reduction measures:
Source Control:
Choose low-noise equipment: Give priority to motors, hydraulic pumps (such as low-pulsation swash plate plunger pumps), and fans (with high-efficiency and low-noise blade design) with low noise levels.
Optimize drive strategy: Perform variable frequency control on the motor to avoid operation at resonant speed; optimize the pressure and flow control strategy of the hydraulic system to reduce unnecessary impact and pulsation.
Optimize structural design: Increase the rigidity and damping of the test bench structure to prevent the resonance frequency from falling within the main working frequency band; optimize the connection design to reduce gaps and looseness.
Propagation path control (sound insulation):
Soundproof enclosure/room: Install a soundproof enclosure or room around the entire test bench or major noise sources (such as hydraulic pump stations and motors). Use multi-layer composite sound insulation panels (such as steel plate + damping layer + sound absorption layer), and seal doors, windows, and pipeline penetrations.
Localized sound barriers: Noise barriers are installed between the noise source and operators/sensitive areas.
Propagation path control (vibration isolation):
Equipment vibration isolation: Install vibration sources such as drive motors, hydraulic pump stations, gear boxes, etc. 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: Use flexible connections (high-pressure hoses, bellows) for hydraulic and air lines, and secure them with elastic hangers/supports to prevent vibration transmission from rigid connections. Install pipe dampers or damping coatings on long pipes.
Foundation Vibration Isolation: For particularly sensitive tests or where low frequency noise is an issue, the entire rig foundation can be isolated using a “floating floor” or large vibration isolators.
Propagation path control (sound absorption):
Sound absorption treatment: Lay high-efficiency sound-absorbing materials (such as centrifugal glass wool, rock wool, porous sound-absorbing foam) on the inner walls, ceilings, and local barrier surfaces of the soundproof enclosure/room to absorb reverberation sound and reduce the internal sound pressure level.
Airflow Noise Control:
Muffler: Install a muffler at the inlet and exhaust ports of the cooling fan (resistive muffler is suitable for medium and high frequencies, reactive muffler is suitable for low frequencies).
Optimize air duct design: Reduce elbows and sudden changes in cross-section to maintain smooth airflow and reduce eddy current noise. The inner wall of the air duct can be treated with sound absorption.
2. Aircraft-grade hydraulic system noise
The aircraft hydraulic system provides high-pressure power for flight control systems, landing gear retraction and extension, braking, reverse thrust, etc.
1. Main noise sources:
Hydraulic pump: It is the main source of hydraulic noise on the aircraft.
Flow/pressure pulsation: The periodic suction and discharge of oil by the plunger of a plunger pump (most commonly used in aviation) produces inherent flow and pressure pulsations, which are the core of fluid noise.
Mechanical noise: bearings, valve plate/cylinder friction, swash plate mechanism vibration.
Cavitation noise: Insufficient oil suction by the pump or too low local pressure causes the oil to vaporize and produce bubbles. The bubbles burst in the high-pressure area and produce high-frequency impact noise.
Piping system:
Fluid noise: High-pressure, pulsating oil flowing at high speed in a pipeline generates turbulent and eddy noise, which is exacerbated when flowing through elbows, valves, and areas with changes in pipe diameter.
Pipeline vibration noise: Fluid pulsation and turbulence excite pipeline vibration, especially when the excitation frequency is close to the natural frequency of the pipeline, resonance occurs, generating strong noise and radiating to the structure.
Cavitation noise: Cavitation occurs when the local flow velocity is too high or the pressure is too low due to improper design.
valve:
Throttling noise: When the oil passes through the valve port (such as servo valve, pressure control valve, check valve) at high speed, it generates injection noise and turbulence noise, with more high-frequency components ("howling").
Pressure shock: Rapid opening and closing of valves (especially solenoid valves) causes sudden pressure changes and produces water hammer noise.
Accumulators: Gas-filled (nitrogen) accumulators absorb pressure pulsations, and the compression and expansion of the gas can produce noise (especially at high frequencies). Slight noise may also be caused by the movement of the bladder or piston.
Actuator: When the actuator moves, the internal oil flow, seal friction, and piston rod and support friction will generate noise, but it is usually smaller than that of pumps and valves.
Fuel tank: Noise is generated by the return oil impacting the oil surface, oil agitation, and bubble bursting. Vibration of the tank structure can also radiate noise.
System resonance: The entire hydraulic system (pump-pipeline-valve-load) may form a fluid-structure coupled resonance system, generating abnormal noise under certain working conditions.
2. Main noise reduction measures:
Source Control:
Choose 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 up pre-compression/pressure relief grooves) to reduce the inherent flow/pressure pulsation.
Pump source filtering: Install a hydraulic filter/vibration absorber near the pump outlet. Common types:
Accumulator type vibration absorber: Utilizes airbag/piston accumulator to absorb pressure pulsation of a specific frequency band (charge pressure needs to be precisely adjusted).
Helmholtz vibration absorber: It consists of a cavity and a short tube, and has a significant effect on absorbing pulsations of specific frequencies.
Resistive damper: uses porous materials or narrow slits to dissipate pulsating energy (good effect on high frequencies).
Pipeline vibration absorber: Use a special flexible pipeline (such as steel wire braided reinforced hose, hose with damping layer) to attenuate pulsation transmission.
Optimize valve design: Use low-noise valve core design (such as multi-stage throttling, anti-cavitation valve port) and optimize the flow path inside the valve to reduce turbulence.
Avoid cavitation:
Ensure that the pump absorbs sufficient oil (sufficient pipe diameter, low flow resistance, and reasonable oil tank design).
The system is designed to avoid local low pressure areas.
Use hydraulic oil with good anti-cavitation performance.
Control valve action: Optimize control algorithms 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 through high-quality elastic vibration isolators is one of the most critical measures that can effectively reduce the vibration and noise transmission of the pump.
Pipe Vibration Isolation/Damping:
Secure the pipes with suitable elastic supports/clamps to avoid rigid contact with the aircraft structure.
Wrapping/covering damping materials (such as constrained layer damping tape, damping paint) on the pipeline can significantly reduce the vibration radiation noise of the pipeline.
Use high-pressure hoses or pulsation attenuation hoses (with special internal structures to absorb pulsation) in critical areas.
Optimize piping layout, reduce sharp bends, and avoid resonant lengths.
Propagation path control (sound insulation):
Partial sound insulation cover: Install a lightweight sound insulation cover on the pump or valve group that is particularly noisy (consider heat dissipation).
Sound-absorbing material: Sound-absorbing material is laid on the inner side of the hydraulic compartment (such as the equipment compartment) to absorb the reverberation sound in the compartment.
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 system's main operating frequency avoids the natural frequency of critical structures or fluid pipelines.
Fuel tank design: Baffles are used to reduce oil return impact and bubbles; ventilation design is optimized; the fuel tank structure is strengthened to reduce radiation.
Summarize
The noise sources of the test bench are more complex and have greater power, so noise reduction focuses on soundproof enclosures, overall vibration isolation (pump station, motor, foundation), large sound absorbers, and air duct silencers.
Noise control in aircraft hydraulic systems focuses more on source suppression (low-pulsation pumps, vibration dampers, valve optimization) and transmission path blocking (pump vibration isolation, pipe damping, local sound insulation/absorption), and must strictly consider aviation constraints such as weight, space, fire protection, and heat dissipation.
Commonalities: Both are highly dependent on comprehensive measures such as 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 often requires a combination of multiple 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 aviation, weight and space constraints make source control and efficient damping/isolation technologies particularly important.
Of course, we are professional in all of the above. Sanyuan Environment is a professional sound environment comprehensive service provider , providing you with one-stop noise control solutions.