Modeling noise generated by industrial chiller systems using a hybrid statistical energy simulation based on experimental and finite element methods.
Open Access
- Author:
- Wells, Stephen Matthew
- Graduate Program:
- Acoustics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- March 02, 2020
- Committee Members:
- Stephen A Hambric, Dissertation Advisor/Co-Advisor
Stephen A Hambric, Committee Chair/Co-Chair
Timothy A Brungart, Dissertation Advisor/Co-Advisor
Karl Martin Reichard, Committee Member
George A Lesieutre, Outside Member
Dennis K Mc Laughlin, Special Member
Victor Ward Sparrow, Program Head/Chair - Keywords:
- Acoustics
Vibration
Vibroacoustics
Hybrid Modeling
Acoustic Radiation
Industrial Chillers
Noise
Noise Modeling
Statistical Energy Analysis
Finite Element
Acoustic Measurements
Vibration Measurements
Compressor
Statistical Model
Physics - Abstract:
- A modeling methodology is developed to predict the acoustic radiation from a Carrier 19XR industrial chiller using a hybrid statistical energy simulation approach, based on experimental and finite element methods. Currently, the driving structural dynamics, forcing functions, and resulting vibroacoustic responses of large industrial chillers are not well understood due to the structure’s vibroacoustic complexity. The ability to model, simulate, and mitigate the noise generated from a 19XR chiller would introduce the opportunity to provide high capacity chillers to low-noise applications, thus eliminating the need for remotely located facilities built specifically to contain the chiller equipment. The underlying physics and sources responsible for noise generation are identified using vibroacoustic measurements captured from a 19XR chiller that provides space cooling and dehumidification across the western part of the University Park campus at The Pennsylvania State University. Mobility and acoustic intensity measurements indicate that the 19XR chiller radiates sound efficiently near the ring frequency of the condenser. Additionally, the vibroacoustic potential of the discharge pipe is largest in the frequency ranges where the compressor impeller generates strong blade passing frequency tonal forcing functions. As the compressor speed is adjusted to maximize the chiller performance, multiple discharge pipe modes have the potential to be driven, further amplifying the acoustic radiation. Moreover, structural resonances that radiate significant energy are driven above the critical frequency of both the condenser and discharge pipe structures, enabling efficient acoustic radiation into the surrounding environment. A statistical model consisting of six (6) subsystems and four (4) forcing functions is used to represent the vibroacoustic behavior and simulate the noise generated by the 19XR chiller. The subsystem parameters used to model the flow of vibroacoustic energy through the structure (i.e., the modal densities, loss factors, and coupling loss factors) are generated using finite element, statistical element, and experimental methods. The coupling loss factors used to represent the transfer of energy between the discharge pipe and condenser structures could not be adequately represented using traditional methods. The complexity of this joint requires an experimental statistical energy approach, where measured conductances, energies, and internal loss factors are used to infer actual coupling loss factors. The accuracy of this approach is confirmed by comparing model simulations to discharge pipe and condenser measurements. The forcing functions induced by the compressor could not be measured directly, nor predicted. Inference methods are used first to estimate the structure-borne forces at the flanged interface between the compressor and discharge pipe, and next, to estimate the fluid-borne power injected into the refrigerant. The inferred forces are heavily dependent on the operating condition of the chiller, therefore, a database of forcing functions are developed for a broad range of operating conditions. Initial model simulations indicate that the structure-borne and fluid-borne compressor sources have roughly equal contribution to the chiller vibroacoustic response. Moreover, model simulations show that forces generated by the jet of refrigerant impinging on the internal structure within the condenser are not significant contributors to chiller vibration and noise generation. Comparisons between the model simulations and a database of measurements show that a model comprised of a statistical representation of the 19XR chiller, predicts the acceleration and radiated sound pressure spectra within three (3) decibels. This fidelity is enough to support design-level decision making and simulate the effects that material, geometric properties, and acoustic treatments have on the vibroacoustic performance of the structure. The simulations suggest that the discharge pipe and condenser structural resonances must be addressed to reduce the amount of noise generated by the 19XR chiller. In addition, a software application based on the 19XR vibroacoustic model, has been developed to quickly evaluate design changes and possible noise mitigation strategies.