汽車油箱燃油晃動CFD模擬分析

2016-08-31 by:CAE仿真在線來源:互聯(lián)網(wǎng)

汽車燃油系統(tǒng)是汽車至關(guān)重要的部件之一,它關(guān)系到每個乘客的生命安全。在剎車和啟動過程中,燃油對油箱壁撞擊所產(chǎn)生的壓力影響到整個燃油系統(tǒng)的穩(wěn)定性,壓力變化引起的振動噪聲也是衡量整車舒適性的重要指標(biāo)之一。因此,燃油晃動一直是燃油系統(tǒng)開發(fā)過程中需要研究的重點和難點問題。使用Fluent軟件運用VOF方法對汽車燃油箱進(jìn)行了汽車加速/剎車過程中的燃油晃動模擬,可以得到燃油晃動過程中油箱壁的壓力分布和壓力變化,為燃油系統(tǒng)的開發(fā)和優(yōu)化提供了指導(dǎo)和理論依據(jù)。

Automobile fuel system is one of the most part of automobile is one of the most important, it is related to the safety of all the passengers. In braking and starting process, the fuel to the fuel tank wall impingement generated pressure influence to the stability of the entire fuel system, pressure changes caused by vibration and noise is also weighs in the amount of vehicle comfort is one of the important indexes. Therefore, fuel sloshing has been fuel system in the process of developing the key issues. Through the use of software fluent with VOF method of automobile fuel tank for automobile acceleration / braking process of fuel sloshing simulation can fuel sloshing in the tank wall pressure distribution and pressure variation. It provides guidance and theoretical basis for the development and optimization of the fuel system.

VOF模型

volume of fluid model

所謂VOF模型是一種在固定的歐拉網(wǎng)格下的表面跟蹤方法。當(dāng)需要得到一種或多種互不相融流體間的交界面時,可以采用這種模型。在VOF模型中,不同的流體組分共用著一套動量方程,計算時在全流場的每個計算單元內(nèi),都記錄下各流體組分所占有的體積率。VOF模型的應(yīng)用例子包括分層流,自由面流動,灌注,晃動,液體中大氣泡的流動,水壩決堤時的水流,對噴射衰竭(jet breakup)(表面張力)的預(yù)測,以及求得任意液-氣分界面的穩(wěn)態(tài)或瞬時分界面。

Prediction failure examples include the application of.VOF in so-called VOF model is a fixed Eulerian mesh surface tracking method. When you need to get a species or variety of mutual incompatibility between fluids interface, can be used in the model. In the VOF model, different fluid components share a set of momentum equation and calculation in the whole flow field of each calculation unit, record the fluid group branch occupies the volume rate model of stratified flow, free surface flow, perfusion, sloshing, liquid bubble flow, the dam burst flow, the jet (jet breakup) (surface tension), and obtained for any liquid Gas interface steady or transient interface.

使用FLUENT軟件進(jìn)行啟動/剎車過程中燃油晃動的模擬,需要將空氣設(shè)置為多相流的主項,燃油設(shè)置為多相流的次相進(jìn)行計算。

Using FLUENT software to start / brake process of fuel sloshing simulation, the need to set the air as the main item of multiphase flow, fuel is set to multiphase flow calculation of the sub phase.

用戶自定義函數(shù)UDF

User defined function UDF

UDF(用戶自定義程序)是FLUENT提供的用戶編程環(huán)境,以解決標(biāo)準(zhǔn)FLUENT本身不能解決的問題。用戶自定義函數(shù)用C語言編寫,使用DEFINE宏來定義。UDF中可使用標(biāo)準(zhǔn)C語言的庫函數(shù),也可使用Fluent提供的預(yù)定義宏,通過這些預(yù)定義宏,可以獲得Fluent求解器得到的數(shù)據(jù)。

UDF (user defined function) is provided by fluent user programming environment, to solve the standard fluent itself will not solve the problem. User defined functions written by C language, using the define macros to define standard C language library functions can be used in the.UDF, also can be provided by fluent predefined macros, through these predefined macros can obtain data obtained in fluent solver.

使用FLUENT軟件進(jìn)行啟動/剎車過程中燃油晃動的模擬,根據(jù)試驗取得的油箱加速度數(shù)據(jù)制定了模型中液相的加速度值,并通過UDF中的DEFINE_SOURCE函數(shù)實現(xiàn)了液相加速度隨時間的變化。DEFINE_SOURCE函數(shù)包含c,t,ds和i四個參數(shù),其中c表示網(wǎng)格,t表示網(wǎng)格線,ds表示源項對所求運輸方程的標(biāo)量的偏導(dǎo)數(shù),用于對源項的線性化,i表示所定義源項對應(yīng)于整個輸運方程。

Using FLUENT software start / brake process of fuel sloshing simulation. According to the test results of tank acceleration data formulated the value of the acceleration of the liquid phase in the model, and through the UDF define source function to achieve the liquid phase acceleration with the change of time.DEFINE_SOURCE source function contains C, t, DS and I four parameters, where C said grid, t denotes the grid lines, DS said source term for the partial derivatives of the scalar transport equation for the source term linearization I defined source term corresponds to the transport equation.

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