Wind noise from A-pillar and side view mirror of a realistic generic car model, DriAver

Interior noise of a production car is a total contribution mainly from engine, tyres and aerodynamics. At high speed, wind noise can dominate the total interior noise. Wind noise is associated with the unsteadiness of the flow. For most production cars, A-pillar and side view mirror are the regions where the highly separated and turbulent flows are observed. This study quantifies the wind noise contribution from A-pillar and side view mirror with respect to the interior noise of a generic realistic model, DrivAer. The noise sources are obtained numerically from the flow-structure interactions based on the unsteady Reynolds averaged Navier stokes (URANS) while the noise propagation is estimated using Curle's equation of Lighthill acoustic analogy. The sound pressure frequency spectrum of the interior noise is obtained by considering the sound transmission loss from the side glass by using the mass law for transmission loss. The study found that the noise from the A-pillar is higher than the noise from the side view mirror in the whole frequency range. Near the end of the A-pillar component contributes the highest radiated noise level with up to 20 dB louder than that at the front part of the A-pillar

Mathematical modelling of fineness ratio effects on aerodynamic characteristics of an airship design using computational analysis

Airships used to be the primary passengers' air transportation means before the jet aircraft took over their role. This happened due to the operational safety concerns after several fatal accidents involving the airships. In recent times however, modern airship designs have been improved and their operational efficiency is said to be better than jet aircraft in many areas. This leads to the idea that airships can be used to revolutionize the current mass public transportation means that are facing several issues of low operational effectiveness and worsened traffic congestion. Though recent airship designs have many advantages, they are not developed for use as a mass public transportation vehicle. To accommodate more passengers onboard, these airship designs might be required to be sized or scaled up and this subsequently affects their aerodynamic performance due to their modified external shape. Therefore, in developing successful airship designs for public transport purposes, it is important for designers to fully understand the effect of the design on the performance of the airship. The external shape design changes can be aptly captured by design fineness ratio parameter of the airship, which is defined as the ratio of the airship's length to its maximum width. Nonetheless, there is a general lack of aerodynamic models that are established for airship design purposes and this is the main identified gap to be addressed in this study. Specifically, the aim of this research work is to establish the effects of design fineness ratio of an airship towards its aerodynamic performance. The Atlant-100 airship is chosen as the reference design model for this study. An approximate computer-aided design (CAD) model of the Atlant-100 airship is constructed using CATIA software and it is applied in computational fluid dynamics (CFD) simulation analysis using StarCCM+ software. In total, 36 simulation runs are executed with different combinations of values for fineness ratio, altitude and velocity. The obtained CFD simulation results are then statistically analyzed using Minitab software to evaluate the significance of the design fineness ratio effects and formulate the mathematical model between the design fineness ratio and the aerodynamic lift and drag forces of the airship design. From the obtained simulation results, it has been found that smaller fineness ratio for Atlant-100 model will correspond to higher aerodynamic lift and drag forces. As in the case simulated in this study, the smallest fineness ratio of 0.93 has been shown to correspond to the highest value of generated lift coefficient while having similar comparable value of generated drag coefficient with the other fineness ratios. This highlights that a smaller fineness ratio of the airship design is more suitable for the mass public use. In addition, from the statistical analysis done, the effects of the fineness ratio to the generated aerodynamic lift and drag forces can be said to be significant. The constructed mathematical models to capture these effects have also been validated with a few goodness-of-fit tests. For the regression model of fineness ratio impact on the lift coefficient, it has R2 value of 0.941. When its predictive accuracy is tested with some simulated random cases, the maximum error obtained is only 6%. On the other hand, for the regression model of the fineness ratio impact on drag coefficient, the R2 value is 0.962 and the maximum predictive error from the simulation random cases test is only 9%. All in all, it can be concluded that the constructed regression models have a good predictive capability to predict the impact of the design fineness ratio on the aerodynamic performance of the airship. With the results from this study, designers can make use of the regression models to predict the right fineness ratio of the airship design for a given mission profile based on expected aerodynamic performance, or vice versa

Computational Fluid Dynamics (CFD) Study on a Hybrid Airship Design

International audienceThe aerodynamic lift and drag performance is one of the important considerations for hybrid airship configuration design. In conjunction with this, simulation study of aerodynamic characteristics can certainly benefit the process of deriving the best possible configuration for hybrid airship design. The aim of this study is to investigate the trend of aerodynamic lift and drag performance for an airship design in different velocities, altitudes and design fineness ratio using the Star CCM+ analysis tool. The airship model applied in this case study is an approximate model of the Atlant-100 airship. It is found that the airship model with low design fineness ratio typically generates much better aerodynamic lifting force in comparison to those with high design fineness ratio. On the other hand, while the range of estimated drag coefficient values is found to be rather insignificantly different, the presence of effects from the design fineness ratio is still evident. Generally, high design fineness ratio for the airship model seems to produce much lower drag force

Mathematical modelling for effects of fineness ratio, altitude and velocity on aerodynamic characteristics of an airship design using computational fluid dynamics

The external shape design change of an airship can be appropriately captured by design fineness ratio, which is defined as the ratio of airship's length to its maximum width. However, there is a lack of aerodynamic models that have been established for airship design purposes. In conjunction to this realization, the aim of this research work is to establish the effects of design fineness ratio of an airship towards its aerodynamic performance. The Atlant-100 airship is chosen as the reference design model for this study. In total, 36 simulation runs are executed with different combinations of values for the fineness ratio, altitude and velocity. The obtained CFD simulation results are then statistically analysed using Minitab software to evaluate the significance of the design fineness ratio effects. From the results, it has been found that smaller fineness ratio corresponds to higher aerodynamic lift and drag forces. As in the case simulated in this study, the smallest fineness ratio of 0.93 has been shown to correspond to the highest value of generated lift coefficient while having comparable value of generated drag coefficient with the other fineness ratios. This highlights that a smaller fineness ratio of the airship design is more suitable. The constructed mathematical models to capture these effects have also been validated with a few goodness-of-fit tests. For the regression model of fineness ratio impact on the lift coefficient, it has R2 value of 0.941. When its predictive accuracy is tested with few simulated random cases, the maximum error obtained is only 6%. On the other hand, for the regression model of the fineness ratio impact on drag coefficient, the R2 value is 0.962 and maximum predictive error from the simulation random cases test is only 9%. Overall, it can be concluded that the constructed regression models have good predictive capability on the impact of design fineness ratio on the aerodynamic performance of the airship under this study