Search Results

Noise inside the passenger cabin is made up of multiple sources. A significant reduction of the major sound sources such as the engine, wind and tire noise helped to improve comfort for passengers. Therefore, HVAC noise (heating, ventilation and air-conditioning) is unmasked as a primary noise source inside the passenger cabin and has to be taken into consideration when designing passenger cabin sound. While HVAC sound is often evaluated at stop, the most common situation of its use is while driving. In case of fresh air as mode of operation, the HVAC system connected to the environment through the air intake. Any change in the boundary conditions due to on-road driving events and gusts of wind affects the flow field in the HVAC system and in turn influences HVAC noise. This study investigates the effect of mass flow and pressure fluctuations on HVAC noise. In a first step, major influences on the HVAC system are identified in an on-road test.

We present a recently developed computational scheme for the numerical simulation of flow induced sound for rotating systems. Thereby, the flow is computed by scale resolving simulations using an arbitrary mesh interface scheme for connecting rotating and stationary domains. The acoustic field is modeled by a perturbation ansatz resulting in a convective wave equation based on the acoustic scalar potential and the substational time derivative of the incompressible flow pressure as a source term. We use the Finite-Element (FE) method for solving the convective wave equation and apply a Nitsche type mortaring at the interface between rotating and stationary domains. The whole scheme is applied to the numerical computation of a side channel blower.

New power train concepts in the automobile industry will decisively change the familiar car acoustics. Secondary acoustic noise sources will be unmasked and dominate the driver's sound experience. The most important secondary noise source is the air conditioning (AC) system. Before a favorable AC sound can actively be designed, it is necessary to identify the acoustic noise sources and find means to influence them. This paper focuses on the AC outlet module which is, apart from the control unit, the only part visible to the customer. Typical acoustic spectra of flowed-through outlets show a characteristic tonality at about 3000 Hz. The knowledge of its aeroacoustic source mechanisms, the inherent implications for the customer and corrective measures especially in automobile surroundings has been limited so far. To analyze this phenomenon in detail, a simplified model outlet that shows the basic aeroacoustic behavior of a series production outlet was constructed and investigated.

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 listening tests. In a second step HVAC noise was investigated in different environments: HVAC as a component, HVAC as a system (including air ducts and vents) and HVAC system integrated 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.

Reliable tools for the prediction of aeroacoustic noise are of major interest for the car industry and also for the vendors of heating, ventilation and air conditioning (HVAC) systems whose aim is to reduce the negative impact of HVAC noise onto passengers. In this work a hybrid approach based on the acoustic perturbation equations is tested for this purpose. In a first step, the incompressible flow field is computed by means of a commercial finite volume solver. A large eddy simulation turbulence model is used to obtain time resolved flow data, which is required to accurately predict acoustic phenomena. Subsequently, the aeroacoustic sources are computed and conservatively interpolated to a finite element grid, which is used to calculate the sound radiation. This procedure is tested for an HVAC unit, a radial blower and finally for a complete system, which combines these two components.

In electrified vehicles, auxiliary units can be a dominant source of noise, one of which is the refrigerant scroll compressor. Compared to vehicles with combustion engines, e-vehicles require larger refrigerant compressors, as in addition to the interior, also the battery and the electric motors have to be cooled. Currently, scroll compressors are widely used in the automotive industry, which generate one pressure pulse per revolution due to their discontinuous compression principle. This results in speed-dependent pressure fluctuations as well as higher-harmonic pulsations that arise from reflections. These fluctuations spread through the refrigeration cycle and cause the vibration excitation of refrigerant lines and heat exchangers. The sound transmission path in the air conditioning heat exchanger integrated in the dashboard is particularly critical. Various silencer configurations can be used to dampen these pulsations.