MIRA Model Research Articles

Wake Flow Investigation on Notchback MIRA Model by PIV Experiments

To deepen our understanding of the flow field and flow mechanism of a car-like model, in this paper, an experimental investigation of the flow field of MIRA notchback 1/8 scale model is carried out using Particle Image Velocimetry (PIV) method. The tests are conducted in an open circuit wind tunnel at a Reynolds number of 9.16×105. In order to obtain the detailed flow field structure of the notchback model, the PIV method was used to capture the flow field images from three orthogonal directions. By studying the vorticity and velocity vector figures of both the time-averaged and instantaneous states, a three-dimensional flow field schematic of the notchback model is summarized, and the formation mechanism and development process of the vortices are analyzed. This study not only provides an intuitive display of the three-dimensional flow field structure of the MIRA notchback model but, more importantly, it provides a reference for the development of automobile aerodynamic drag reduction by analyzing the flow mechanism, which is beneficial to energy conservation.

Simulation Analysis for Effect of Rear Structure of Hatchback Car on Rear Field Characteristics

The tail shape of the hatchback car is crucial to the rear field. To improve the tail aerodynamic design of the hatchback car, the orthogonal optimization method is used to reveal the rule of different tail structures affecting the aerodynamic drag and lift force considering their interference with each other. First, the different tail structures, such as the top, the side, the bottom and the tail structures, are analysed to reveal the influence of the wake based on the MIRA model. Then, the orthogonal optimization method is applied to investigate the tail shape optimal design considering the mutual influence of each tail structure. The aerodynamic drag coefficient and the lift coefficient are calculated to evaluate the aerodynamic characteristics in the orthogonal analysis. The results show that the angles of the rear windshield and the diffuser has a great influence on the aerodynamic drag. While the diffuser angle have the greatest influence on the lift coefficient. The influence of the rear windshield angle and roof angle is also noteworthy. In a word, the diffuser angle, the rear windshield angle and the roof angle are the key structures for the aerodynamic optimization of the tail of hatchback cars.

A research on aerodynamic characteristics of non-pneumatic tire

Application of non-pneumatic tire (NPT) has been increased during the last decade. The aerodynamic characteristics of the wheel with NPT has been studied due to significance on improvement of handling and reduction of fuel consumption. In this paper, first, an original NPT model was simulated by CATIA software, and the influence of NPT structural parameters on aerodynamic characteristics was studied by Fluent software. The simulation calculation results showed that: the reduction of tire width and spoke length, and the increase of spoke thickness can effectively decrease aerodynamic coefficient. Then, the MIRA model was used to study the influence of NPT on aerodynamic characteristics of the whole vehicle under driving conditions. Studies showed that: NPT increased the resistance of the whole vehicle, and 63.1% of the resistance at the wheels was provided by the front wheels. Finally, the wind tunnel test was conducted to study aerodynamic characteristics of the optimized NPT model under static conditions and verify the simulation calculation.

Aerodynamic Drag Reduction and Optimization of MIRA Model Based on Plasma Actuator

Active flow control of surface dielectric barrier discharge (SDBD) plasma is a technology that converts electrical energy into kinetic energy to achieve flow control. Its main application areas are concentrated in the aviation field. Undoubtedly, few studies have applied it in the field of automobile flow control. Meanwhile, during high-speed driving, there is a serious airflow separation phenomenon at the rear of notch-back cars, which brings a large area of negative pressure to the back of the cars. Due to the huge pressure difference between the front and end of the cars, it will increase the driving drag and fuel cost of the car. In this context, we seek to discuss the control effect on the airflow separation at the rear of the notch-back by using the phenomenological numerical simulation method of plasma flow control. Firstly, the plasma actuator is arranged separately on the rear end of the roof, c-pillar, upper and side of the trunk to study the control effect of airflow separation. After that, the plasma actuators at each position are combined and actuated simultaneously. We try to observe the control effect of airflow separation and select the combination with the best drag reduction effect. In the third stage, an efficient global optimization (EGO) algorithm based on kriging response surface is applied to optimize the supply voltage of the best combination that has been obtained before and obtain the driving voltage parameter of each actuator optimized under this combination. The results show that when plasma actuation is applied at four locations, only the actuation applied to the side of the luggage compartment has a significant drag reduction effect, while in other cases, the drag coefficient will increase. Specifically, drag reduction is better when the actuation is applied at four positions simultaneously. The maximum drag reduction coefficient of the car is reduced by 13.17%.

Transient Simulation Research on Automobile Aerodynamic Lift Based on LBM Method

In order to improve the limitation of steady-state automobile aerodynamic lift characteristics in finite volume method, the Lattice Boltzmann Method (LBM) was conducted on transient simulation of automobile aerodynamic lift. This proposed method utilized adaptive wake refinement feature to obtain a series of regular fluid particles for macroscopic fluid and combined large eddy simulation (LES) with wale-viscosity model to study the transient characteristics of automobile aerodynamic lift. In this numerical investigation, using the international standard automobile MIRA model, the temporal and spatial characteristics of rear velocity field and vorticity field were analyzed, whose results had agreement with the wind tunnel test data. It was showed that the elaborate information of flow field around the car-body and the aerodynamic lift could be more accurately described. A pair of asymmetric non-periodical and inward twisting rear vortexes in the car rear flow field was found, while it squeezed and dragged each other in different eddy scales. This result also indicated the aerodynamic lift to oscillate in a certain amplitude scope, markedly different from the simulated result of steady state automobile aerodynamic lift, which is more close to real driving conditions. DOI: http://dx.doi.org/10.5755/j01.mech.23.6.19847

Revisit Language Modeling Competition and Extinction: A Data-Driven Validation

Understanding language competition and extinction is an interdisciplinary challenge, and math models provide a tool for interpreting linguistic census data and possibly predict the language shift trend at the population scale. In this study, new data from previously examined areas were modeled, specifically Catalan and Spanish in Catalonia, Spanish and English in Houston, Texas, Dutch and French in Brussels, Euskera and Spanish in Spain and French and English in Canada. Three mathematical models of the language competition have been validated. The first is the Abrams-Strogatz model, which treats populations as having two monolingual groups. The second is the Castello model, which considers bilingual speakers. The third is the Mira model, which considers language competition when the two languages have high similarities. It was found that the some of the data matched Abrams-Strogatz original model, but some divergences could still be addressed. It was also found that the Mira model needs some improvement in how it treats the differences between languages.

Optimization and design method for a rough rear surface on the notchback MIRA model

In order to explore the optimization and design method of the rough surface on a vehicle body, a pitted rough surface, a convex rough surface and a grooved rough surface are respectively arranged at the rear of the MIRA model. Computational fluid dynamics and wind tunnel tests are adopted to analyse the relationships between the aerodynamic drag and the factors of the rough surface. The distance L and the height H of the surface roughness are considered as the design variables, and the aerodynamic drag coefficient CD is the objective evaluation function. Sample points are obtained by the Latin hypercube sampling method, and the kriging approximate model is set up according to the sample points and the response values. Then the multi-island genetic algorithm is used as the optimization algorithm to find the optimum solution. The aerodynamic effects of the rough surface model, with optimization and without optimization, are compared and analysed. Experimental and simulation results show that the aerodynamic drag coefficient further decreases after parameter optimization and that the optimization method is valid and general. The results obtained may provide a helpful reference and guidance for future rough surface applications on a vehicle body.

Effect of Car Rear Shape on Pollution Dispersion in Near Wake Region

Dispersion of vehicle exhaust gas is a primary source of air pollution in urban areas. Thus, it has become an important subject in the automotive field. This paper consists of two parts. First, the fastback MIRA model was selected as study object and a standardκ-εtwo-equation turbulence model was used. The simulation results were compared and analyzed with experimental data. The feasibility of the turbulence model and grid strategy was then verified, and the results were used in the next research step. Second, we used propane as tracer gas while ignoring the effect of the vehicle wake field force on this gas. The tracer gas diffusion in the wake flow field was then simulated through fastback, notchback, and square-back MIRA models. This study focuses on analyzing the characteristics of wake field diffusion effects, particularly in the near wake of a vehicle.

Simulation of Interference Characteristics of the Model Supporting Beams with Different Forms of Section in Wind Tunnel Test

In order to study the effects of the supporting beams with different forms of section on the aerodynamic characteristics of car models. Model supporting beams with three different forms of section were designed based on standard MIRA model. The commercial CFD software - Ansys Fluent was used to simulate the three-dimensional flow field around the standard MIRA model installed with three different kinds of supporting beams. With comparisons between the drag coefficients, pressure distributions and velocity distributions around the wheels with the different supporting beams, the reasons for the differences in aerodynamics are analyzed and advices were given for helping choosing the supporting beam with minimal disturbance to reduce the correction error.

Numerical Optimization Research on Rear Characteristic Angles Based on MIRA Model for Aerodynamic Drag Reduction

The rear characteristic angles of the passenger car in this study were defined as the inclination angle of rear window and the bottom inclination angle of aft based on the MIRA model. The numerical optimization method was used to analyze the influence of combined variation of two angles on the external flow field and the CD of the passenger car, in which we combined genetic algorithm with the CFD simulation to reduce aerodynamic drag by seeking the relatively optimal combination of two parameters above. The study reveals that when the combination of the inclination angle of rear window and bottom inclination angle of aft is 25oand 0.067o, the total pressure and streamline distribution in the flow fields of the MIRA model are improved greatly and the CD is reduced compared with the worst combination. This conclusion will have profound guiding significance in the aerodynamic design of the rear styling and shape of a car.

Research on Aerodynamic Characteristics of a Simplified SUV Model

The aerodynamics characteristics of square Mira model were researched by simulation, the drag coefficient and the aerodynamic characteristics around model were achieved with analysis of velocity and pressure distribution. Based on results, the angle of rear wind window, the angle of underbody diffuser and the front transition radius were changed, the drag and lift coefficients were achieved. The conclusions provide reference for how to reduce drag coefficient of SUV

Design for Wind Tunnel Testing of Scaled Model by CFD Method

The numerical investigations presented in this paper deal with wind tunnel testing scheme design for 1/4 scaled MIRA model including supporting system. Based on the structure of aerodynamic and aero-acoustic full scale wind tunnel, using computational fluid dynamics (CFD), focus on MIRA model and supporting system, the drag force of scaled models and supporting system were calculated. By comparing with the wind tunnel testing results and drag force coefficient of reference, it is certain that the wind tunnel testing scheme is available and effective and that the value calculated by CFD is in good agreement with experiments.

Parallel large eddy simulation of turbulent flow around MIRA model using linear equal‐order finite element method

AbstractA parallel large eddy simulation code that adopts domain decomposition method has been developed for large‐scale computation of turbulent flows around an arbitrarily shaped body. For the temporal integration of the unsteady incompressible Navier–Stokes equation, fractional 4‐step splitting algorithm is adopted, and for the modelling of small eddies in turbulent flows, the Smagorinsky model is used. For the parallelization of the code, METIS and Message Passing Interface Libraries are used, respectively, to partition the computational domain and to communicate data between processors. To validate the parallel architecture and to estimate its performance, a three‐dimensional laminar driven cavity flow inside a cubical enclosure has been solved. To validate the turbulence calculation, the turbulent channel flows at Reτ = 180 and 1050 are simulated and compared with previous results. Then, a backward facing step flow is solved and compared with a DNS result for overall code validation. Finally, the turbulent flow around MIRA model at Re = 2.6 × 106 is simulated by using approximately 6.7 million nodes. Scalability curve obtained from this simulation shows that scalable results are obtained. The calculated drag coefficient agrees better with the experimental result than those previously obtained by using two‐equation turbulence models. Copyright © 2007 John Wiley & Sons, Ltd.

The K-band intensity profile of R Leonis probed by VLTI/VINCI

We present near-infrared K-band interferometric measurements of the Mira star R Leonis obtained in April 2001 and January 2002 withVLTI/VINCI. The April 2001 measurements indicate a center-to-limb intensity variation (CLV) that is clearly different from a uniform disk (UD) intensity profile. We show that these measured visibility values are consistent with predictions from recent self-excited dynamic Mira model atmospheres. We derived high-precision Rosseland diameters for the two epochs and, together with literature estimates of the distance and the bolometric flux, we find linear radii of 350+50 -40 R_⊙ and 320+50 -40 R_⊙ andeffective temperatures of 2930 ± 270 K and 3080 ± 310 K, respectively.

Metallicity effects in Mira variables: a model study

AbstractM-type Mira models with a moderate deviation from solar metallicity (2x and 0.5 x) have been computed and compared to solar-metallicity models. Selected effects of abundance changes on pulsation properties, atmospheric stratifications, spectral features (colours) and surface brightness distributions are discussed.

Effects of molecular contamination of IR near-continuum bandpasses on measurements of M-type Mira diameters

We study the contamination of six near-continuum bandpasses (0.82, 0.92 and 1.04 μm, H, K, L*) that are commonly used for interferometric measurement of diameters of M-type Mira variables. Centre-to-limb variations (CLVs)of intensity predicted by Mira models of Bessell, Scholz & Wood and Hofmann, Scholz & Wood show slight to substantial effects of molecular absorption by H 2 O (H, K, L*), OH (H), CO (H), TiO (0.82, 0.92, 1.04), VO (0.82) in different models which may lead to spurious observed 'continuum diameters'. In particular, two-component-type CLVs in H, K and L*, composed of the continuum light of the inner disc and the light emitted by H 2 O molecules in the outer atmosphere may affect visibilities in such a way that UD fits result not only in strongly wavelength-dependent but also, in case of single-baseline observations, in baseline-dependent diameters. Similar effects occur when sub-intervals of the H, K and L* bandpasses are considered. Continuum contamination depends on parameters of the Mira models and may vary substantially with variability phase and cycle. Observational evidence supporting model predictions is assembled, and strategies of deriving physically meaningful Mira diameters are outlined. The period-radius relation and consequences for the pulsation mode of Miras have to be rediscussed.

From wind to superwind - The evolution of mass-loss rates for Mira models

Dynamical atmosphere models were calculated for a large grid of variables with Mira-like properties satisfying the Iben radius-luminosity-mass relationship for evolving AGB stars. Their masses ranged from 0.7 to 2.4 solar masses, and their periods from 150 to 800 days. All were fundamental-mode pulsators, had solar metallicity, and included effects of dust. The mass-loss rate increases as an approximately exponential function of time, reaching 0.00001-0.0001 solar masses/yr. Further evolution is dominated by the powerful wind, which strips the star's envelope from the core. This 'superwind', a remarkably robust effect, occurs for all initial stellar masses and all modeling parameters that have been tested. Models with very low metallicity also show the effect, but at higher luminosities, which has intriguing implications for the number of supernovae in early low-metallicity populations and for the chemical evolution of galaxies.

Photospheres of Mira Variables

Mira variables form an important subgroup of the red giant stars which are typical representatives of stars showing burnt material at their surfaces. Since the photospheres of Miras are not in hydrostatic equilibrium but are characterized by spherically very extended density stratifications, their properties and emitted spectra differ substantially from those of non-Miras, and any attempts to analyse Mira spectra by means of conventional techniques must fail. Non-hydrostatic models are needed for analysis work.We computed a small set of exploratory M type (solar abundances) Mira model photospheres whose density distributions were taken from an improved modification of a pulsation model proposed by wood (1979). Besides the fundamental model parameters, i.e. mass, luminosity and radius (or effective temperature), the parameters of the density stratification (e.g. the heights of the density discontinuities at the shock front positions, or the effective gravity acting between two successive shock fronts) must be treated as free parameters within certain limits, owing to insufficient knowledge of the velocity stratification entering the pulsation model. Typical density and temperature stratifications are shown in Fig. 1 of Scholz (1987). Both CO lines, measuring the outflow and infall velocities of matter between the shock fronts, and selected moleculer band features (colors) were found to react sensitively to adjustments of the model parameters. As an example, Fig.1 shows the differences between CO line profiles computed from the near-maximum model of Fig.1 of scholz (1987) (Fig.1a) and those computed from a model in which the effective gravity between the shock fronts was increased by a factor of 1.5 (Fig. 1b). The same velocity stratification was adopted in of monochromatic radii proves to be a powerful tool of diagnostics of Mira photospheres (Scholz and Takeda 1987; Bessell et al. 1987).

Mira model photospheres

The temperature stratifications and the emitted fluxes of Mira model photospheres based upon the extended density distribution of a pulsation model differ substantially from those of conventional model photospheres based upon a hydrostatic density distribution. Hence, the interpretation of Mira spectra by means of hydrostatic models is inadequate, and the spectral characteristics of Miras may deviate significantly from those of non-Miras.