## 1 Introduction  
The vehicle interior noise caused by high-speed external flow is one of the critical issues for product developers to consider in a design state. The improvement of the NVH (noise, vibration, and harshness) technologies has led to a significant reduction in vehicle noise caused by vibration from an engine, the interaction of tire/road, and transmission system [1]. The sound power of aerodynamic noise is known to increase in proportion with the sixth to eighth power of the vehicle speed. On the other hand, the structure-borne noise from the engine, tire/road interaction, and transmission system is only proportional to the first to third power of the speed [2]. This fact implies that the aerodynamic noise should be more dominant as the running speed of the vehicle increases. Aerodynamic noise becomes even more critical due to the rapid commercialization of electric vehicles without traditional combustion engine noise. The physical process of the interior transmission of external flow disturbances can be understood by three sequential mechanisms: external flow excitation on the windshields of a vehicle, the vibrational response of the vehicle windshields to the external flow disturbances, and the acoustic response of a cabin room to the windshield vibration. The external flow fluctuations can be categorized into two kinds of pressure fields. One is an incompressible pressure field due to convected turbulent boundary-layer flow, and the other is compressible pressure fluctuation due to aerodynamic noise. The former is called hydrodynamic pressure or pseudo-sound, and the latter is called acoustic pressure. A few studies focused on developing an effective algorithm to separate incompressible and compressible pressure fields to investigate the transmission characteristics of those through a cabin's wall panel. [PERSON] et al. [3] applied a direct noise computation code of the compressible three-dimensional Navier-Stokes equations to accurately predict external aerodynamic and acoustic wall pressure fluctuations due to a car side mirror over a flat plate. They separated the aerodynamic and acoustic components using the wavenumber-frequency diagram of the surface pressure field. However, there were significant differences in the power spectral density of surface pressure fluctuations between the predicted and measured ones. [PERSON] et al. [4] proposed an effective signal processing technique based on wavenumber-frequency transform. They also successfully decomposed the surface pressure field on the side window of an automobile into two distinct hydrodynamic and acoustics surface pressure fields by using the wavenumber-frequency diagram of the surface pressure field. [PERSON] et al. [5] applied the wavenumber-frequency transform to the external surface flow fields of a high-speed train running at a speed of 300 km/h in an open space to assess the relative power levels due to each pressure field. However, these studies did not compare with measured data to validate the predicted surface pressure fields. An appropriate test model is essential to quantitatively assess the indoor cabin noise of an automotive due to external flow disturbances in an actual situation. [PERSON] et al. [6] reported the numerical and experimental results on the interior noise due to the airflow around the A-pillar and the side mirror of a generic vehicle model developed by a consortium of German automotive manufacturers. The model is built in such a way that only the noise transmission through the front side window is relevant. This study used different CFD solvers to predict the transient pressure loading. [PERSON] et al. [7] also compared numerous numerical solvers of computational fluid dynamic and vibracooustic methods to accurately predict interior noise transmission excited by a pillar vortex of a simple land vehicle model, the Hyundai Simplified Model (HSM). These studies focused on benchmarking different numerical methods without a detailed analysis of related physical and numerical issues. [PERSON] et al.