畢 業(yè) 設(shè) 計（論 文）任 務(wù) 書設(shè)計（論文）題目：轎車驅(qū)動橋設(shè)計 學(xué)生姓名：發(fā)任務(wù)書日期：2015年12月30日 任務(wù)書填寫要求1．畢業(yè)設(shè)計（論文）任務(wù)書由指導(dǎo)教師根據(jù)各課題的具體情況填寫，經(jīng)學(xué)生所在專業(yè)的負責(zé)人審查、系（院）領(lǐng)導(dǎo)簽字后生效。此任務(wù)書應(yīng)在畢業(yè)設(shè)計（論文）開始前一周內(nèi)填好并發(fā)給學(xué)生。2．任務(wù)書內(nèi)容必須用黑墨水筆工整書寫，不得涂改或潦草書寫；或者按教務(wù)處統(tǒng)一設(shè)計的電子文檔標(biāo)準格式（可從教務(wù)處網(wǎng)頁上下載）打印，要求正文小4號宋體，1.5倍行距，禁止打印在其它 上 。3．任務(wù)書內(nèi)填寫的內(nèi)容，必須 學(xué)生畢業(yè)設(shè)計（論文） 的情況 一 ， ，應(yīng) 經(jīng) 所在專業(yè) 系（院） 領(lǐng)導(dǎo)審 后 可 填寫。4．任務(wù)書內(nèi) 學(xué)院 、 專業(yè) 名 的填寫，應(yīng)寫 文 ，不 寫 字 。學(xué)生的 學(xué)號 要寫號，不 寫?后2￠或1￠ 字。 5．任務(wù)書內(nèi) 要￡?文￥ 的填寫，應(yīng)按?§currency1'“?學(xué)院?“畢業(yè)設(shè)計（論文）?寫fifl 的要求書寫。6． 年月日 日期的填寫，應(yīng) 按?–標(biāo)GB/T 7408—94§ 據(jù)? ?·格式、 ??·、日期 ???”? fi…的要求，一‰用 ? 字書寫。` 2002年4月2日 或 2002-04-02”。畢 業(yè) 設(shè) 計（論 文）任 務(wù) 書1．?畢業(yè)設(shè)計（論文）課題應(yīng)′?的目的：1.? ?畢業(yè)設(shè)計ˉ學(xué)生?˙、¨ ??所學(xué) ?,?ˇ — 學(xué)生 用所學(xué)專業(yè) ? ? 工 題的 。2.?設(shè)計? 根據(jù)所 車 發(fā)動 、 ￡ 動 要求 ，查? a、書 ， …驅(qū)動橋 體設(shè)計 ，設(shè)計其 要???，并o行 ，ˉ學(xué)生學(xué) a的 、? 、整 正 ˉ用工具， ? 、? “學(xué) ?的?? ?；— 學(xué)生 用? 設(shè)計 ? 工 題的 ， 立正 的設(shè)計思想。同??ˇ學(xué)生獨立 處 專業(yè) 題的 ，ˉ學(xué)生初步具 工 設(shè)計 從事“學(xué) ?的 。為從事?專業(yè)工作打下堅 的?礎(chǔ)。 2．?畢業(yè)設(shè)計（論文）課題任務(wù)的內(nèi)容 要求（包括原始 據(jù)、? 要求、工作要求 ）：要內(nèi)容 要求：汽車驅(qū)動橋??功用是增扭、降 ，改 轉(zhuǎn)矩的傳遞 向，同?驅(qū)動橋還要承受作用于路面車架或車身之?的垂直 、縱向 橫向 ，以 制動 矩 反作用 矩 。汽車驅(qū)動橋一般由 減 、差 、半軸、驅(qū)動橋殼 組 。要求 ：根據(jù)所 車 發(fā)動 、 ￡ 動 要求 ， …驅(qū)動橋 體設(shè)計 ；校核滿載?的驅(qū)動 ，對汽車的動 o行 算；對 要???` 減 、差 o行設(shè)計 強度計算；繪制??圖 圖。工作要求：結(jié)合 習(xí) 開?， 設(shè)計。所需條?： ?工具 手段（儀 、儀? ）； 的手冊文￥ a； 車輛 設(shè)備；電腦 CAD軟?并 上網(wǎng)? a。 畢 業(yè) 設(shè) 計（論 文）任 務(wù) 書3．對?畢業(yè)設(shè)計（論文）課題 果的要求〔包括圖?、 物 硬?要求〕：對?畢業(yè)設(shè)計課題 果的要求為：1.在 、? a 的?礎(chǔ)上， …驅(qū)動橋 體設(shè)計 ，校核滿載?的驅(qū)動 ，對汽車的動 o行 算，對 要???` 減 、差 o行設(shè)計 強度計算。2.符合要求的??圖 圖。2.符合fifl的畢業(yè)設(shè)計說明書一份。3.翻譯一篇1萬印刷符以上 課題 的專業(yè)外文 a。 4． 要￡?文￥： [1] 陳家瑞.汽車構(gòu)造（上下冊）（第3版）[M].北京： 械工業(yè)出版社，2009.[2] 余志生.汽車 論(第5版)[M].北京： 械工業(yè)出版社，2009.[3] 王望予.汽車設(shè)計(第4版)[M].北京： 械工業(yè)出版社，2004.[4] 喻凡，林逸.汽車系統(tǒng)動 學(xué)[M].北京： 械工業(yè)出版社，2005.[5] 濮良貴，紀名剛. 械設(shè)計（第八版）[M].北京：高 教育出版社，2006.[6] 徐石安.汽車構(gòu)造——底盤工 [M].北京：清華大學(xué)出版社，2008.[7] 王–權(quán)，龔–慶.汽車設(shè)計課 設(shè)計指導(dǎo)書[M].北京： 械工業(yè)出版社，2010.[8] .汽車設(shè)計[M].北京：北京大學(xué)出版社.2008.[9] §汽車工 手冊 .汽車工 手冊（設(shè)計篇）[M].北京：人 ??出版社，2001.[10] 王 .汽車底盤設(shè)計[M].北京：清華大學(xué)出版社，2010.[11] 安.AutoCAD2011 文版 械設(shè)計 教 [M].北京： 械工業(yè)出版社，2010.[12] 林清安. ?Pro/ENGINEER 5.0 文版??設(shè)計?礎(chǔ) [M].北京：電子工業(yè)出版社，2010.[13] 王 .CATIA V5 械（汽車） CAD/CAE/CAM ?教 [M].北京：人 ??出版社，2007.[14] 陳 ， .驅(qū)動橋橋殼 ? 結(jié)構(gòu) [J].汽車 用? ，2011，07期.[15] .轉(zhuǎn)向驅(qū)動橋 ? [J].? ???，2011，05期.[16] 正 ，徐 .4WD 車驅(qū)動橋的設(shè)計 [J]. 北汽車工業(yè)學(xué)院學(xué) ，2011，03期. 畢 業(yè) 設(shè) 計（論 文）任 務(wù) 書5．?畢業(yè)設(shè)計（論文）課題工作o度計?：2015-11-04￠2015-12-312016-01-02￠2016-03-052016-03-06￠2016-03-202016-03-21￠2016-04-202016-04-21￠2016-05-052016-05-06￠2016-05-26題，查￡任務(wù)書，? 整 課題 ￡? a；o行畢業(yè)設(shè)計 ， 開題 ?，畢業(yè)設(shè)計外文 a翻譯，畢業(yè)設(shè)計￥?；驅(qū)動橋 體 設(shè)計，校核滿載?的驅(qū)動 ，對汽車的動 o行 算；對驅(qū)動橋 要???` 減 、差 o行設(shè)計 強度計算，繪制??圖 圖；￥?畢業(yè)設(shè)計草§，o行 期currency1查；畢業(yè)設(shè)計說明書…§?由指導(dǎo)'師審?，指導(dǎo)'師審核? 后，￥?畢業(yè)設(shè)計 “?a，準備??；根據(jù)學(xué)院統(tǒng)一要求，o行畢業(yè)設(shè)計（論文）??。所在專業(yè)審查fifl：? 負責(zé)人： 2016 年 1 月 22 日畢 業(yè) 設(shè) 計（論 文）開 題 報 告設(shè)計（論文）題目：轎車驅(qū)動橋設(shè)計 學(xué)生姓名：2016 年 1 月 8 日 開題報告填寫要求1．開題報告（含“文獻綜述”）作為畢業(yè)設(shè)計（論文）答辯委員會對學(xué)生答辯資格審查的依據(jù)材料之一。此報告應(yīng)在指導(dǎo)教師指導(dǎo)下，由學(xué)生在畢業(yè)設(shè)計（論文）工作前期內(nèi)完成，經(jīng)指導(dǎo)教師簽署意見及所在專業(yè)審查后生效；2．開題報告內(nèi)容必須用黑墨水筆工整書寫或按教務(wù)處統(tǒng)一設(shè)計的電子文檔標(biāo)準格式打印，禁止打印在其它紙上后剪貼，完成后應(yīng)及時交給指導(dǎo)教師簽署意見；3．“文獻綜述”應(yīng)按論文的框架成文，并直接書寫（或打印）在本開題報告第一欄目內(nèi)，學(xué)生寫文獻綜述的文獻應(yīng) 15 （ ）；4． 年月日 日期的填寫，應(yīng) 按 標(biāo)GB/T 7408—94 據(jù) 交 格式 交 日期 時 的要求，一?用￠￡? ￥書寫。?“2004年4月26日”或“2004-04-26”。5 開題報告（文獻綜述）￥§currency1按'§ “??書寫，? fi1.5fl。畢 業(yè) 設(shè) 計（論文） 開 題 報 告 1． –畢業(yè)設(shè)計（論文）?題?·， 據(jù)所查?的文獻資料，???寫 1000￥”?的文獻綜述： 一 前…‰車驅(qū)動橋 ‰車的?要 成之一，驅(qū)動橋處 動`′動?的?ˉ，?要由?˙¨ ?¨ ，車?′動 ?驅(qū)動橋? ˇ成，其—本 由′動 或 ¨ ′ 的 ，并 – 的 給”?驅(qū)動車?，? 作用 a 車架或車 之 的 直`， ?` ??`[1]。‰車車橋的 ?o式 設(shè)計 對‰車的 ? ?要 ，?對‰車的? ?動` 經(jīng) ?? ?? 動 及 作 直接 [4]。隨著近年來油價上漲，‰車的運輸成本?越來越高，因此在保證‰車動` 的前提下，提高其燃油經(jīng) 就顯得尤為?要。為 降低油耗， 僅要在發(fā)動 環(huán)節(jié)上節(jié)油，而且?要在′動?中˙ 量損耗。這就必須在發(fā)動 的動`輸出之后，在從發(fā)動 —′動 —驅(qū)動橋這一動`輸送環(huán)節(jié)中尋找 量的損耗。在這一環(huán)節(jié)中，發(fā)動 動`輸送者，? 整個 的心臟，而驅(qū)動橋則 動` 化為 量的最終執(zhí)?部 。因此，采用 優(yōu)良且與發(fā)動 匹 比較高的驅(qū)動橋便成 效的節(jié)油措施之一[2]。隨著‰車工業(yè)的發(fā)展及‰車技術(shù)的提高，驅(qū)動橋的設(shè)計 制造工藝都在日益完善。二 ?題研究領(lǐng)域的現(xiàn)狀 動態(tài)及發(fā)展方?在新政策 ‰車產(chǎn)業(yè)發(fā)展政策 中，在2010年前，我 就要成為世界?要‰車制造 ，‰車產(chǎn)品滿足 內(nèi)市場 部 需求并批量進入 際市場；2010年，‰車生產(chǎn)企業(yè)要o成若干馳名的‰車 摩托車 零部件產(chǎn)品品牌；??市場競爭o成幾家具 際競爭`的 型‰車企業(yè)集團，`爭到2010年跨入世界500強企業(yè)之列，。同時，在這個新的‰車產(chǎn)業(yè)政策描繪的藍圖中， 含許多涉及產(chǎn)業(yè)素質(zhì)提高 市場環(huán)境改善的綜–目標(biāo)，著 ? 。 而， 的 ， 內(nèi)‰車產(chǎn)業(yè)的現(xiàn)狀 產(chǎn)業(yè)政策的目標(biāo) 的fi 。 1994年 ‰車工業(yè)產(chǎn)業(yè)政策 并執(zhí)? 來， 內(nèi)‰車產(chǎn)業(yè) ? 顯 化，企業(yè) 效益 顯改善，產(chǎn)業(yè)集中 一 提高。 ， 期 來 中 ‰車產(chǎn)業(yè)發(fā)展的 低水?? 設(shè) 題， 從 本上得到 。多 企業(yè)家 計，在新的‰車產(chǎn)業(yè)政策的 下， 會 越來越多的‰車生產(chǎn)企業(yè)按 市場 ?ˇ成企業(yè) ， 現(xiàn)優(yōu)?￠￡ 資?￥?。驅(qū)動橋 ‰車的一§?要 成，因此currency1'研究優(yōu)化驅(qū)動橋設(shè)計對 改善目前 內(nèi)的‰車產(chǎn)業(yè)具 “ ?要的作用。 內(nèi)生產(chǎn)??式驅(qū)動橋的?家較多，品? 格?較fi，其 質(zhì)量—本上 fl滿足 產(chǎn)工 的–用要求。 內(nèi)驅(qū)動橋多采用?式或?式制動 ，?式制動 · 為 ?式 fi?式???型，與 ?進產(chǎn)品比， 內(nèi)驅(qū)動橋??′動 ?技術(shù)水?”較低， 足之處?要 ?方 ：一 ??， ?，?§ 零件材料與制造工藝與 產(chǎn)品 比?在一 ?fi，?在整§?量 §…較 ，–用‰ ? `；二 技術(shù) 對′后，?? 采用 ˉ式?˙?¨ ¨式制動 ?進 ?。在??式工 驅(qū)動橋中 ? ˉ式?˙?¨ ¨式制動 ， 提高工 驅(qū)動橋產(chǎn)品技術(shù)水?的? 之一。 ˉ式?˙?¨ 動 現(xiàn) 在”?車? 的 ， ? ?用車ˇ的— `， 顯提高??驅(qū)動工 的越 經(jīng) ，目前用的最多的 式fi 動?¨ˉ，這? 產(chǎn) 驅(qū)動橋技術(shù)發(fā)展的必 ?。文獻：[1] 家 .‰車?造（上下 ）（第3 ）[M]. ： 工業(yè)出 ，2009.[2] 生.‰車 論(第5 )[M]. ： 工業(yè)出 ，2009.[3] .‰車設(shè)計(第4 )[M]. ： 工業(yè)出 ，2004.[4] ? ，a .‰車?統(tǒng)動`學(xué)[M]. ： 工業(yè)出 ，2005.[5] .‰車?造——??工 [M]. ：?? 學(xué)出 ，2008.[6] o， .‰車設(shè)計? 設(shè)計指導(dǎo)書[M]. ： 工業(yè)出 ，2010.[7] .‰車設(shè)計[M]. ： 學(xué)出 .2008.[8] ‰車工 ?委員會.‰車工 （設(shè)計 ）[M]. ：? 交?出 ，2001.[9] .‰車??設(shè)計[M]. ：?? 學(xué)出 ，2010.[10] ? .‰車車 設(shè)計[M]. ： 工業(yè)出 ，2007.[11] ??,? ?.‰車動`?統(tǒng)計 匹 及 價[M]. ： 工 學(xué)出 ，2009.[12] 良 ，紀名剛. 設(shè)計（第八 ）[M]. ：高 教育出 ，2006.[13] 范欽珊，殷雅俊.材料`學(xué)（第2 ）[M]. ：?? 學(xué)出 ，2008.[14] ? .AutoCAD2011中文 設(shè)計 例教 [M]. ： 工業(yè)出 ，2010.[15] a? .完fi精?Pro/ENGINEER 火5.0中文 零件設(shè)計—礎(chǔ)入門[M]. ：電子工業(yè)出 ，2010.[16] 登 .CATIA V5 （‰車）產(chǎn)品CAD/CAE/CAMfi精?教 [M]. ：? 交?出 ，2007.[17] 豐 .‰車驅(qū)動橋虛擬設(shè)計?統(tǒng)研究[J]. 設(shè)計與制造，2009，04期.畢 業(yè) 設(shè) 計（論文） 開 題 報 告 2．本?題要研究或 的 題 擬采用的研究 段（? ）： 一 本?題要研究或 的 題本?題?要研究的對象 家用轎車的驅(qū)動橋設(shè)計?！胲囼?qū)動橋一般由?˙¨ ?¨ 半 驅(qū)動橋? ˇ成。 據(jù)發(fā)動 ¨ 及動` 要求 ，并 文獻來確 驅(qū)動橋 §設(shè)計方案，對 零件的`學(xué)特 驅(qū)動橋的動` 進?校核計 ，繪制 零件及其 圖， 此完成本次設(shè)計方案。二 擬采用的研究 段（? ）?要技術(shù)a線 ：1.查?轎車驅(qū)動橋 資料，深入 驅(qū)動橋 成，確 驅(qū)動橋 §設(shè)計方案；2. 熟悉CATIA，Pro/E,CAD 繪圖軟件；3. 校核驅(qū)動橋滿載時的驅(qū)動`，對‰車的動` 進?驗 ，對?要零部件??˙¨ ?¨ 進?設(shè)計與強 計 ；4.?用計 輔助繪圖軟件繪制三維零件及其 圖。畢 業(yè) 設(shè) 計（論文） 開 題 報 告 指導(dǎo)教師意見：1．對“文獻綜述”的 語：學(xué)生 fl在收集查?畢業(yè)設(shè)計（論文）?題 文獻資料的—礎(chǔ)上 ?寫文獻綜述，文獻綜述調(diào) ?晰 格式 范，符–文獻綜述的特點與要求。2．對本?題的深 ? 及工作量的意見 對設(shè)計（論文） 果的 測：本?題深 ? 適中，工作量符–畢業(yè)設(shè)計要求；經(jīng)? 真? 的準備工作，應(yīng) fl?期完成畢業(yè)設(shè)計（論文）工作。3. 同意開題：√ 同意 □ 同意指導(dǎo)教師： 2016 年 03 月 13 日所在專業(yè)審查意見：同意 負責(zé)?： 2016 年 04 月 07 日畢 業(yè) 設(shè) 計（論 文）外 文 參 考 資 料 及 譯 文譯文題目： 方程式賽車的空氣動力制動裝置 學(xué)生姓名：專 業(yè)：所在學(xué)院：指導(dǎo)教師：職 稱：年 1 月 20 日Aerodynamic Brake for Formula Cars Abstract:In the last years,in formula racing cars championships, the aerodynamic had reached an ever more important stance as a performance parameter. In the last four seasons, Red Bull Racing Technical Officer had designed their Formula 1 car with the specific aim to generate the optimal downforce, in relation to the car instantaneous setup. However, this extreme research of higher downforce brings some negative effects when a car is within the wake of another car; indeed, it is well known that under these condition the aerodynamic is disturbed, and it makes difficult to overtake the leading car. To partially remedy this problem, Formula 1 regulations introduced the Drag Reduction System (DRS) in 2011, which was an adjustable flap located on the rear wing; if it is flattened, allowing to reduce the downforce, increasing significantly the velocity and, therefore, the chances to overtake the leading car. Vice versa, when the flap is closed, it ensures a higher grip, which is very useful especially in medium-slow speed turns. Keeping the focus on the rear wing, but by shifting attention from the increased top speed to increase the grip in the middle and slow speed curves, we decided to study a similar device to the DRS, but with the opposite effect. The aim is to design an aerodynamic brake integrated with the rear wing. In particular, the project idea was to sculpt, on the upper surface of the wing (pressure side), a series of “C“ shaped cavity, nor-mally covered by adequate sliding panels. These cavities, when they are discovered, at the begin-ning of the braking phase, produce a turbulence and additional increase downforce, lightening the load on the braking system and allowing the pilot to substantially reduce slippage and to delay the braking. Since it seems that the regulations adopted by the FIA Formula 1 Championship do not allow such a device, it has been decided to apply the concept on a Formula 4 vehicle. This paper describes the design and analyzes the effects of these details on a standard wing cavity, using acommercial CFD software.Keywords: Aerodynamic Brake, Cavity, Dynamic Effects, Fluid Dynamic Simulation1 Problem FormulationIn this paper, the realization of an aerodynamic brake integrated in a rear wing of a formula car has been consi-dered. The first step consists in the choice of an appropriate aerodynamic appendix. In particular, it was decided to study an Italian Formula 4 race car [1], being a category in the first stages of development. Also, the regula-tion of this championship is easy to find and the car is characterized by uniformity of the mechanics and the air-foils. Therefore, taken note of the technical regulation on FIA website, it was decided to study the upper airfoil, of which was shown a dimensioned drawing (Figure 1). It is an aluminum alloy wing, with a chord line of 237.9 mm and a height of 54.2 mm.Formula 4 championship will provide the use of a 4T heat engine(Otto/Beau de Rochas cycle): it can be na-turally aspirated or turbocharged, with maximum power in the order of 120 kW (160 HP). Considering the weight of the car and the race tracks of the championship, it is predicted a maximum speed of 230 km/h (64 m/s). Regarding the operating conditions, an air temperature of 300K was assumed at atmospheric pressure.Briefing Description of Airfoil BehaviorConsidering an airfoil, there are several elements that have a specific nomenclature:1) Mean camber line: locus of points halfway between the upper and lower surface as measured perpendicular to the mean chamber line itself;2) Leading edge: the most forward point of the mean camber line;3) Trailing edge: the rearmost point of the mean camber line;4) Chord: the straight line joining the leading edge with the trailing edge; 5) Upper surface: the upper boundary of the profile; 6) Lower surface: the lower boundary of the profile; 7) Thickness: the distance between the lower surface and the upper surface.The different airfoil shapes are marked by a logical numbering system which was introduced by the U.S. federal agency NACA. This system consists of four digits which have a definite meaning: the first digit indicates the maximum camber in hundredths of chord; the second digit represents the location of maximum camber along the chord from leading edge in tenths of chord; the third and fourth give the maximum thickness in hundredths of chord.When an airfoil is moving relative to the air, it generates an aerodynamic force, in a rearward direction at an angle with the direction of relative motion. This aerodynamic force is commonly resolved into two components: lift and drag. Lift is the force component perpendicular to the direction of relative motion while Drag is the force component parallel to the direction of relative motion. These forces are studied at different angles of attack which is the angle at which an airfoil cleaves fluid. The experimental data show that CL varies with the angle of attack: more precisely, at low angles of attack the lift coefficient CL varies linearly with α. In a region characterized by a linear trend, the flow moves smoothly over the airfoil and is attached to the back of the wing. As soon as α increases, the flow tends to separate from the surface of the airfoil, creating a region of “dead air” behind the profile. A briefing flow analysis of the physical phenomenon in question in order to understand better what is happening in the latter case is reported. It is clear from Figure 2 that the speed at the trailing edge tends to increase, with a strong reduction of the pressure, while in the stagnation point the speed tends to be zero and pressure rises sharply. It creates an adverse pressure gradient, thus particles of fluid move from the trailing edge to the stagnation point, and then it has a rapid separation of the boundary layer below. Stagnation point does not have a stable position in these conditions because there is not pressure recovery. The recirculation generated by the detachment of the boundary layer creates first vortex that causes a wake vortex. It is necessary to study the turbulent behavior of the fluid that meets the wing, through the Navier-Stokes equations in order to consider the stall of the wing:where u(x, t) is the instantaneous velocity, ρ the medium density, μ the viscosity and f the applied force.This system of equations is a system of partial differential equations that describe the behavior of a Stokesian fluid: the fluid can be considered to be continuous. There is an analytical solution only in simplified cases, while solutions in the other cases can be obtained using simplified methods of numerical analysis. The most straightforward method for the numerical simulation of turbulent flows is direct numerical simulation DNS which discretizes the Navier-Stokes equations. It resolves the entire range of turbulent length scales thus the description of the flow is so detailed that the validity of the simulation is similar to an experiment. The computational cost is proportional to Re3, thus it is necessary to use a different solution studying turbulent flows at high Reynolds, because the computational resources required by a DNS would exceed the capacity of the most powerful computer currently available. In practical applications, the knowledge of the average quantities is enough to solve the problem of a turbulent flow; the basic idea of the technique RANS (Reynolds Averaged Navier-Stokes Equations) is to derive only the average parameters (mediated in time) from Navier-Stokes equations, reducing the enormous computational cost required by DNS. In practice, the turbulent motion consists of a mean motion and fluctuation over time. Using the decomposition of Reynolds:Where u( x, t) is the instantaneous velocity, u( x, t) is the average velocity u′( x, t) is the speed fluctuating, through Navier-Stokes equations it’s possible to obtain the Reynolds averaged equations. The equations for the mean motion obtained are similar to Navier-Stokes equations with the exception of the divergence of the stress tensor Reynolds: the system resulting from the Navier-Stokes equations is closed, while the system resulting from the RANS simulation is not open because Reynolds tensor introduces 6 additional unknowns. The problem mentioned is known as the problem of closure of turbulence which is solved by introducing models for the turbulent fluctuations which have to reproduce the action of fluctuating terms on mean motion.The K-ε model is one of the most common models of turbulence, even if it is not appropriate in the case of strong adverse pressure gradients. It is a model with two equations: it includes two additional transport equations to represent properties of the turbulent flow and effects such as convection and diffusion of turbulent energy. The first variable transported is the turbulent kinetic energy, k. The second variable transported is the turbulent dissipation, ε; the second variable determines the scale of turbulence, while the first variable k determines the energy in the turbulence. There are two formulations of the K-ε models: the standard k-epsilon model and the RNG k-epsilon model.In the standard k-epsilon model, eddy viscosity is determined by single length scale turbulence, so the turbulent diffusion is calculated only through a specified scale, whereas in reality all scales of motion will contribute to turbulent diffusion.The approach RNG (Re-Normalisation Group), a mathematical technique that can be used to obtain a model similar to the k-epsilon turbulence, presents a modified equation ε, which attempts to explain the different scales of turbulence through changes at the term of production of turbulence. The equations used are: a) Kinematic Eddy Viscosity b) Turbulence Kinetic Energyc) Dissipation RateClosure coefficient for standard k-epsilon model:1. Project DescriptionThe purpose of this project is to improve the race performance, reducing the breaking distance and increasing the bending speed.So, we decided to intervene on the drag generated by the wing during the breaking, and also on the grip provided by downforce, function of velocity. To explain the lift, and then the downforce, reference may be made to the wing of an airplane, observing its section. The latter is asymmetric, the top has a profile longer than the bottom: when the wing moves, it separates the relative flow in two parts, so the air layers scroll faster in the top. The outflow over the wing undergoes a boost and then is aerodynamic brake for formula cars accelerated towards the tail at a higher velocity than the air under the wing, which follows a shorter path. So the two currents are reunited in the tail after a same time interval, without creating imbalances. This is not just the facts, but as a first approximation, we can refer to this model. In reference to the Bernoulli trinomial law, since in the lower flow velocity is lower than in the upper, the pressure under the wing has to be greater than that above the wing. Therefore, the difference between the two pressures generates a resultant directed upwards, that is the lift, which holds the aircraft in the air. In detail, lift can be expressed as:where: ? ρ is the medium density; ? V is the air velocity; ? A is the reference surface; ? Clis a lift dimensionless coefficient; ? α is the wing angle of attack.In racing cars, the wing is mounted upside down and the vertical thrust towards the ground (downforce): this is correlated to the tires grip coefficient. The running resistance depends on its front section, its forward speed, the density of the medium and a drag coefficient. The drag coefficient (Cd) depends on the object shape and size of the object, the medium density and viscosity, the surface roughness, and the object velocity. The aerodynamic resistance (in general fluid dynamics), or drag, is related to a large number of factors, as shown by the formula:where: ? ρ is the medium density of the; ? V is the air velocity; ? A is the reference surface (in case of aircraft is the wing surface, the car front surface); ? Cd is a drag dimensionless coefficient; ? α is the wing angle of attack.The overall resistance opposed by a fluid medium to the object forward movement is given, in first approximation, by the sum of the frictional resistance, the wake resistance and the induced resistance of lift. In particular, for a tapered body, the flow resistance is given by friction (laminar and/or turbulent), that is the rubbing of the surface against the medium. For this purpose we introduce the concept of boundary layer: it’s the dynamic range, laminar or turbulent, in which internal current speed is subject to strong gradients (continuous changes), due to the viscosity of the fluid. It can be considered as the area that undergoes a disorder, and the velocity is zero on the layer surface (Figure 3).The thickness of the boundary layer is very small, and it is of one order of magnitude lower than the overall dimensions of the object, that generates the viscose perturbation. Then, inside the boundary layer, the tangential shear stress is “dense”. For this reason in the layer is exerted an intense dissipative braking action, converting part of the movement in thermal agitation. The dissipative action limits the relative velocity between the object and the fluid, which surrounds it. In a turbulent boundary layer, the viscous stresses are added also the stresses, due to the exchange of transverse momentum; these actions increase with the fluid density. The chaos of the turbulent fluid motions implies higher thermal dissipation, so the braking opposing force, in turbulent flow conditions, is greater than that of the laminar regime. The resistance generated, in this way, is affected by the surface roughness: moreover, the rougher surfaces ignite earlier and more easily the turbulent condition in the flow, and then, determine higher resistances. Therefore, it was decided to design some ducts, on the pressure side of the wing, initially covered by special sliding plates, for increasing the aerodynamic drag and downforce [2].2. Wing DesignThe first phase of the design is to draw the profile of the wing with a CAD software. In this way, it is possible to make a CFD simulation, to evaluate the aerodynamic performance of the wing, in terms of downforce and drag, and estimate the useful angles of attack before stall phenomenon occurs [3]. In fluid dynamics the stall is a reduction of the lift coefficient due to an increase of the angle of attack or due to the incident velocity decrease on an aerodynamic profile, such as an airfoil, a propeller blade or a turbomachinery rotor. The minimum value of the angle of attack for which the stall occurs is called critical angle of attack. This value which corresponds to the maximum lift coefficient, changes significantly, depending on the particular profile or on the considered Reynolds number [4]. Similarly, the profile of the active cavities has been reported, and appropriate simulations were performed. In this way it was possible to estimate the sizes and configurations to achieve the project target. Based on the data collected, the application of these cavities on the wing is studied, evaluating the performance on the different possible arrangements of these cavities. At this moment only 2D simulations have been performed, and a 3D series is considered as future improvement of the project. The models, the different configurations and the results obtained from all the cases mentioned above, will be shown in detail in the following paragraphs.Geometry ModelingTo approximate the operating conditions of the wing, a control conduit with the dimensions shown in Figure 4(a)has been chosen. Regarding to the active cavity, the geometry is illustrated in Figure 4(b). The space surrounding the geometry of the aerodynamic and the cavities was discretized using a special dedicated software available as ANSYS package. Furthermore, to observe the progress of the boundary layer, it was built on a reference mesh of 5 layers, with growth factor 1.1, starting from the adjacent profiles of height 0.18 mm (Figure 5). To this purpose, a sizeable set of data was created by means of sufficiently accurate numerical simulations, to derive initial values. The simulations were performed on 3-D models in kinematic similarity using a commercial CFD simulation code, ANSYS/Fluent. The turbulence model was the k-ε realizable, with second order accuracy. Each model was meshed to ensure a y+max~ 5, a necessary condition for adopting the enhanced wall treatment, since the quality of the grid has a relevant importance on the accuracy and stability of the numerical simulation.Commercial software allows the “plastering” of cell layers to the critical boundaries of the control volume, which are obviously, in this case, the wall surfaces of the hub, casing and blades. In these zones the usual practice is that of creating a completely structured boundary layer, specifying whenever possible both the height of the first row of cells and the “growth ratio”, i.e. the rate that determines the height of the successive cells. In this process, the height of the first row of cells is usually determined via an empirical formula that gives the value of a wall-based local Reynolds number, denoted by y+ (y+ = u*·y/v where u*= (τwall/ρ)1/2, with τwall being the wall shear stress). For the wing analysis control volume was split in several smaller sub-volumes, to achieve a more consistent set of faces and to better exploit the possibility of creating a locally more refined grid. The choice of the boundary conditions was made as follows: it was performed heuristically, starting from the preliminary sizing data, calibrating them by means of a first simulation, adjusting the values by iteratively resetting the outlet static pressure on the near-wake radial area downstream of the trailing edge. Through subsequent simulations the values of the inlet total pressure and temperature were refined as well in order to ensure conservation of the mass flow rate (the so-called “mass flow inlet condition” was adopted). The turbulent parameters were the turbulence intensity I =( k) U . Rotational periodicity was imposed on all lateral channel surfaces. The number of cells is about 65,000 elements. Finally, the starting boundary conditions are:? fluid: it is considered air as an ideal gas at constant viscosity; ? input data: the pressure of 101325 Pa and temperature of 300 K represent the operating conditions. boundary conditions: ? inlet → mass flow rate; ? outlet → pressure outlet; ? for both, the conditions relating to the model were set on intensity and length scales, with values of 5% and 0.03 m (?1/10 of the rope)respectively; ? on the upper and lower walls of the duct it has set the periodicity condition; ? for wing, are set on the condition stationary wall and no slip; ? for the solution a simple high order term and relaxation has been chosen, by setting for all variables a relaxation factor of 0.25.3. Conclusions and Possible ImprovementsThe CFD simulations indicate the effectiveness of active cavities, practiced on a formula car rear wing, in order to achieve an aerodynamic brake. Specifically, we can assert that the configuration with the best balance between downforce and drag is that with extended ducts over the entire top surface of the aerodynamic (Fl= ?365.172N, Fd= 65.88N). Finally, by exploiting the selectivity of sliding panels, as previously explained, it can be realized different wing configurations, depending on the needs required by the race and the sensitivity of the driver.As regards any improvements, to be made on the performance testing of the brake (the object of study of this paper), more CFD simulations could perform, using a vertical bulkhead on the