Refine Your Search

Search Results

Technical Paper

Automotive HVAC noise reduction

2018-06-13
2018-01-1519
The Heating Ventilation and Air Conditioning system (HVAC) is a compact and complex system designed to provide thermal comfort inside the car cabin. The system is composed of various components : fan, flaps, thermal exchangers, filters and specific turned ducts allowing thermal conditioning and airflow distribution to car cabin areas. Nowadays, as thermal engine noises are reduced and electrified car sales are increasing, the HVAC could be a major noise source inside the car cabin that could induce significant discomfort to passengers. HVAC noise issues are well known and solved. Many of them are related to electrical motor of the fan, such as ticking and harmonic noises. The remaining noises are mainly aeroacoustic linked to the fan and interactions between HVAC components and airflow. HVAC behavior also consists of transfer paths and acoustic transparency responsible of emerging noises.
Technical Paper

Experimental Investigation of Low-Frequency Vibration Patterns in Automotive Disk Brake Systems: Utilization Study for Modal Simulation Methods

2018-06-13
2018-01-1513
Increasing demands on automotive comfort as well as diminishing vehicle noise levels draw new attention towards low-frequency vibration and noise issues of disk brake systems such as creep groan and moan. In view of this problem, the experimental investigation of relevant phenomena is within the scope of this article. The related experiments concerning two different setups have been performed at a drum driven suspension and brake test rig. Both assemblies consisted of a front axle corner including all parts of the integrated brake system. In order to gain understanding of characteristic triggering mechanisms and fundamental subsystem interactions, and moreover, to verify the suitability of modal methods for simulative evaluations of creep groan or moan, specifically elaborated Operating Deflection Shape (ODS) techniques have been applied. Via analyses of four different creep groan emergences, global stick-slip cycles between disk and pads are revealed.
Technical Paper

Efficient Prediction of Flow-Induced Sound Sources and Emission from a HVAC Blower

2018-06-13
2018-01-1518
The most commonly used method for prediction of flow-induced sound emission of rotating systems is the Ffowcs Williams-Hawkings method. A shortcoming of this method in the application to blowers is, however, that only the rotation of the impeller can be included in the calculation, but not reflections of the sound from the housing, rotor blades and attached ducts. This paper introduces a Finite Element method that correctly maps both the sound sources rotating with the impeller and the reflections of the sound from the rigid surfaces of the components of the blower. For the prediction of flow-induced sound a hybrid approach is employed using separate CFD and acoustic simulations. It is based on a decomposition of flow (incompressible part) and acoustic (compressible part) quantities and is applicable to high-Reynolds-number and low-Mach-number flows. It features only a scalar unknown (i.e. the acoustic velocity potential), thus reducing the computational effort significantly.
Technical Paper

Application and Simulation of Microperforated Panels in HVAC Systems

2018-06-13
2018-01-1514
By applying the Finite Element method in combination with non-matching inter- faces, we demonstrate the potential of the widely used Johnson-Champoux-Allard (JCA) porous absorber model to mimic the characteristics of microperforated pan- els (MPPs) up to a frequency of 8 kHz. Usually a MPP is connected in series with an air cavity of certain length against a hard backed boundary to be acoustically effective. Although the panel itself can be seen as a locally reacting material, the combination of MPP and air volume is not locally reacting anymore. As soon as the sound waves impinge at an oblique angle, the generally used impedance boundary condition to model porous behavior produces more and more unrealistic results. Thus, to overcome these limitations in the higher order mode frequency regime, we resolve the entire geometry of the acoustic domain by solving a modified Helmholtz equation and modeling the MPP as an equivalent fluid.
Technical Paper

Convected Wave Equation for a Moving Body in an Inhomogeneous Flow

2018-06-13
2018-01-1517
Sound field around a moving body in a mean flow of fluid is commonly estimated with Ffowcs Williams and Hawkings equation. Similarly as Lighthill’s aeroacoustic analogy, Ffowcs Williams and Hawkings equation includes sound propagation phenomena in moving and inhomogeneous media, such as convection and refraction, implicitly within the source terms on the right-hand side of the equation. Consequently, the equation is primarily applicable when the surrounding fluid is quiescent everywhere outside the source region. In this work, we follow the approach of Phillips and derive an exact aeroacoustic equation for a moving body in an inviscid and isentropic flow, which separates source and propagation terms on the two sides of the equation. As such, the equation can be used even when the sound propagation effects have a significant influence on the sound field.
Technical Paper

Experimental Analysis on the ‘Exact’ Cremer Impedance in Rectangular Ducts

2018-06-13
2018-01-1523
Cremer impedance, first proposed by Cremer (Acustica 3, 1953) and then improved by Tester (JSV 28, 1973), refers to the locally reacting boundary condition that can maximize the attenuation of a certain acoustic mode in a uniform wave guide. One limitation in Tester’s work is that it simplified the analysis on the effect of flow by only considering high frequencies or the well cut-on modes. This approximation is reasonable for large duct applications, e.g., aero-engines, but not for many other cases of interest, with the vehicle intake and exhaust system included. A recent modification done by Kabral et al. (Acta Acustica united with Acustica 102, 2016) has removed this limitation and investigated the ‘exact’ solution of Cremer impedance, which reveals a huge difference between the ‘exact’ and classic solution in the low frequency range. Consequently, the ‘exact’ solution can lead to a much higher low-frequency attenuation level.
Technical Paper

Stop whistling! A note on fluid driven whistles in flow ducts.

2018-06-13
2018-01-1524
The generation mechanism and possible counter measures for fluid driven whistles in low Mach number flow duct networks are discussed. The vortex sound model, where unstable shear layers interact with the acoustic field and act as amplifiers under certain boundary conditions, is shown to capture the physics well. Further, for the system to actually whistle an acoustic feedback to the amplifying shear layer is also needed. The demonstration example in this study is a generalized resonator configuration with annular volumes attached to a straight flow duct via a number of small holes, perforations, around the duct’s circumference. At each hole a shear layer is formed and the acoustic reflections from the resonator volumes and the up and downstream sides provides a possible feedback to them.
Technical Paper

A fluid-structure interaction scheme for prediction of flow-induced low frequency buffeting noise

2018-06-13
2018-01-1521
The analysis of the acoustic behavior of flow fields has gained importance in recent years, especially in the automotive industry. The comfort of the driver is heavily influenced by the noise levels and characteristics, especially during long distance drives. Simulation tools can help to analyze the acoustic properties of a car at an early stage of the development process. This presentation focuses on the low-frequency booming noise which can be a significant noise component under certain operating conditions. As a first step in the fluid-structure interaction workflow, the flow around a series-production vehicle is simulated, including passenger cabin and underhood flow. The complexity of this model poses extensive demands on the simulation software, concerning meshing, turbulence modeling and level of parallelism. We conducted a transient simulation of the compressible fluid flow, using a hybrid RANS/LES approach.
Technical Paper

Modeling of HVAC noise in a simplified car model

2018-06-13
2018-01-1522
To assure high comfort for vehicle passengers, the interior noise has to be designed to be low in volume as well as in a pleasant way. Vehicle’s HVAC (heating, ventilation and air-conditioning) noise becomes increasingly audible when the main sound sources are acoustically optimized. Thus, the Sound Quality of HVAC noise needs to be evaluated early in the development process. For assessing the Sound Quality of HVAC noise, suitable evaluation criteria as well as the knowledge of the acoustics of the new HVAC system are required. Suitable evaluation criteria were identified using a listening test. In a second step HVAC noise was investigated in a simplified car model. The model was designed acoustically similar to a series vehicle. Thus, the size as well as the interior paneling of a series vehicle was approximated by using sound-absorbing and -reflecting material.
Technical Paper

A Steady-state based Investigation of Automotive Turbocharger Compressor Noise

2018-06-13
2018-01-1528
The present work aims at a physics-based understanding of the aerodynamically generated noise in centrifugal compressors, and its propagation in turbocharging systems such as those typically employed in the automotive industry. Given the unsteady nature of acoustics, the project this work is part of will have to develop towards correlation of acoustic sources and far field noise by means of LES investigations, with the final aim of addressing noise suppression technologies. However, simpler steady state investigations prove to be a valuable means of tackling the technical challenge, as well as a solid base for more in-depth future unsteady analyses. In this initial phase of the work, a steady state RANS (Reynolds Averaged Navier-Stokes) analysis is carried out on a specific compressor geometry, and acoustic data are extracted by means of the aeroacoustics models available in a commercial software (such as Curle and Proudman).
Technical Paper

Mechanical Retractor Noise Evaluation on Electrodynamic Shaker: Test Procedure

2018-06-13
2018-01-1532
Modern vehicles are driven with various speeds over specific rough road tracks to detect the presence of annoying buzz, squeak and rattle sounds. As known in the occupant safety industry, the mechanical locking systems of seat belt retractors can be significant noise sources when excited by road vibrations. Along with the retractor integration into the vehicle (interface stiffness, efficiency of trims) the retractors affinity to rattle has an important impact on the perceived loudness. A reliable bench test procedure is necessary to quantify the acoustic performance of retractors, verify production quality, and derive realistic acoustic product targets. The vibration input in this specification has been defined as a horizontal 60Hz bandlimited broadband excitation, while the N10 instationary loudness metric has been selected to characterize the retractor acoustic performance.
Technical Paper

Flow noise generation in a pipe bend

2018-06-13
2018-01-1525
Noise generated by low Mach number flow in duct networks is important in many industrial applications. In the automotive industry the two most important are the ventilation duct network and the engine exhaust system. Traditionally, design is made based on rule-of thumb or slightly better by simple semi-empirical scaling laws for flow noise. In many cases, strong curvatures and local deviations from circular cross-sections are created due to outer geometry restrictions. This can result in local relatively high flow velocities and complex flow separation patterns and as a result, rule-of thumb and scaling law methods can become highly inaccurate and uncertain. More advanced techniques based on time domain modelling of the fluid dynamics equations together with acoustic analogies can offer a better understanding of the local noise generation, the propagation and interaction with the rest of the system.
Technical Paper

Influence of compressor recirculation valve and piping design on the acoustic response of a turbocharger

2018-06-13
2018-01-1527
Turbochargers are nowadays, with the emerging technology of downsized combustion engines, an essential part of automotive engines. Turbocharged engines must provide full boost pressure at low engine speed but also avoid over boost at high engine speed. This can only be achieved with a boost pressure control system, as it is the case by multi-stage boosting systems (e.g. R2S), which combine two or more Turbochargers with regulations valves. An integrated recirculation valve in the compressor housing (CRV) acts as a regulating feature in R2S systems. The recirculation process and the piping of such valves can be the root cause of various aero-acoustic problems. The aim of this paper is to conduct an acoustical comparison between three different CRV designs, as a part of centrifugal compressor stage. Investigated are different CRV and piping designs aiming at a compromise in terms of aero-acoustics and performance.
Technical Paper

Localization of BSR Noise Source Using the Improved 3D Intensity Method

2018-06-13
2018-01-1530
A three-dimensional sound intensity probe is employed to identify the components generating the buzz, squeak, and rattle (BSR) noise in the vehicle interior. The 3D intensity probe is advantageous compared to the beamforming or TDOA method: compact overall size, small number of microphones, low-frequency detection capability. Although the 3D sound intensity has been not popular due to various bias errors, but the recent error compensation method is adopted in the work, improving the estimate precision substantially. The filtered cross-power spectral density is used to calculate the intensity avoiding the spectral bias error, and an error map for spatial angles is used to compensate the difference in directivity index around the microphone array. An intensity probe with an even microphone spacing of 30 mm in tetrahedral arrangement is selected for the source localization.
Technical Paper

From Theory to Three-Dimensional Finite Element Models: An Innovative Method for Validation

2018-06-13
2018-01-1536
As a key part of numerical analysis, the modeling process has a tremendous influence on the quality of the results. While there is general awareness concerning uncertainties that arise during modeling, their quantity and sensitivity are rarely known. Hence, modeling can quickly become inaccurate and inefficient. The scope of the present paper is to innovate predictive modeling processes concerning the dynamics of real complex structures by means of linear modal analysis with the finite element method (FEM). The aim is to offer a transparent design catalog relating specific uncertainties to each model component in order to achieve error prevention for engineers dealing with comparable systems. A complex system is simplified and investigated for different levels of detail. Only after the model uncertainties for one level of detail are obtained, the next level of complexity is approached.
Technical Paper

Prediction of interior vehicle noise by means of NARX Neural Networks

2018-06-13
2018-01-1538
In recent years, great interest on NVH characteristics of vehicles has been paid by all the big automotive manufacturers. Interior acoustic comfort is now one of the main key factors in vehicle development process, since it contributes to improved product overall quality. Therefore, in automotive industry advanced NVH refinement needs to work in synergy with all research activities. Assessing the level of experienced noise in interior cabin requires particular arrangements for ensuring adequate measurement accuracy (AC system off, closed window, etc.). The use of parameters such as the level of seat vibration, not affected by the acoustic field conditions inside the vehicle, could facilitate experiments in parallel with engine/vehicle calibration activities.
Technical Paper

Influence of clutch tribodynamics on drivetrain Noise, Vibration and Harshness, (NVH), phenomena

2018-06-13
2018-01-1537
In the modern automotive drivetrain limiting problematic Noise, Vibration and Harshness (NVH) phenomena is a critical task. The result of such phenomena is the aggravation of the driver and in turn a reduced perception of vehicle quality. Each phenomenon is characterised by a distinct irritable frequency range. The aim of the current study is to assess the influence of the surface characteristics of the dry friction clutch components on the drivetrain dynamic behaviour. The dynamics of the system are studied numerically. Surface specific data from the clutch components are critical to understanding the complex engagement process. The coefficient of friction was measured using a pin on disc rig at representative slip speeds, contact pressures and temperatures. To aid the analysis a coordinate measuring machine and infinite focus microscope were used to measure the geometric properties of the constituent components of the drivetrain.
Technical Paper

Vibration Analysis for a 12-DOF Full Car Model with Hydraulic Engine Mounts of Frequency Dependent Stiffness and Damping

2018-06-13
2018-01-1540
Instead of rubber mount, hydraulic mounts have been used underneath power train of vehicles to achieve better ride comfort for a long time. A lumped mass-spring-dashpot model is often used to model a hydraulic mount in vibration analysis of vehicles in the previous studies. While, it was found that modeling the hydraulic mounts as the lumped mass-spring-dashpot model can be justified just when bottom of the hydraulic mount is fixed, which is not the case in a real vehicle where the body with a power train on it is vibrating itself. In this study, another model, to be called a transfer function model, for the hydraulic mount derived based on hydraulic dynamics will be adapted and compared with the lumped mass-spring-dashpot model via vibration analysis of a 12-degree of freedom (DOF) full car model.
Technical Paper

Optimizing Vehicle NVH using Multi-Dimensional Source Path Contributor Paradigm.

2018-06-13
2018-01-1542
Automotive Community is moving towards lightweight vehicle design with more powerful engines. This is increasing the demand for more optimized NVH design. Source-Path-Contributor (SPC) analysis is one of the ways to draw a holistic picture of any NVH problem. In this paper we have studied a very common NVH problem i.e. “Low Frequency Booming Noise and Steering Vibration “, in one of our development model. We have studied all the three dimensions of SPC paradigm and proposed a feasible and optimized solution at the Source, Path as well as the Contributor. For source we focused on driveline optimization. This was done by studying torsional fluctuations. Transfer Path Analysis is done to identify the Critical Paths. Optimization of suspension bush parameter is done using the Dynamic Elastomer Testing machine for improved performance. Finally for the Contributor, Operation Deflection Shape was studied to identify the major panels responsible for deterioration in NVH Quality.
Technical Paper

Comparing Airborne Interior Noise Contribution Analysis Using Exhaust-near Sound Pressure or Volume Acceleration as Source Strength Description

2018-06-13
2018-01-1541
The correct quantification of airborne sources and their transfer to the vehicle interior noise enables vehicle manufacturers to set system targets and to assess interior noise effects of new or modified systems. Measurements on complete vehicles and on test-beds for body, engine, exhaust, tire, HVAC etc. can then be used to estimate interior noise contributions and choose an optimal level of solutions. This study addresses exhaust tailpipe airborne noise emission in a highly controlled situation; indoors and with an exhaust simulator. Two methods of characterization are compared. One method uses the sound pressure very close to the active source as a source strength combined with pressure transmissibility to estimate the interior noise contributions. The other method uses an inverse estimate of the source volume acceleration and the pressure over volume acceleration transfer for the same purpose. The methods of airborne contribution analysis are briefly described.
X