145,978 research outputs found
Assessment of LES, IDDES and RANS approaches for prediction of wakes behind notchback road vehicles
No full textThe capability of Large Eddy Simulations (LES), Improved Delayed Detached Eddy Simulations (IDDES) and Reynolds-Averaged Navier–Stokes Equations (RANS) to predict the flow behind notchback Ahmed body is investigated in the present paper. Simulations consider two specific models, with effective backlight angles of β1=17.8\ub0 and β2=21.0\ub0, respectively. The focus of the study is on the prediction of the expected lateral asymmetry or symmetry of the near-wake flows. Results show that IDDES using coarse computational grids predicts the flow in agreement with LES using finer computational grids. RANS results in inaccurate flow predictions, attributed to its steady formulation relying on turbulence modelling being incapable of dealing with the studied flow. Modal analysis applying Proper Orthogonal Decomposition (POD) suggests the consistency of the wake dynamics between IDDES and LES. The presence of the wake bi-stability is validated by the wind tunnel experiment
On state instability of the bi-stable flow past a notchback bluff body
No full textThe wake of a notchback Ahmed body presenting a bi-stable nature is investigated by performing wind tunnel experiments and large-eddy simulations. Attention is confined to the Reynolds number (Re) influence on the wake state instability within 5 x 10(4) <= Re <= 25 x 10(4). Experimental observations suggest a wake bi-stability with low-frequency switches under low Re. The wake becomes \u27tri-stable\u27 with the increase of Re with the introduction of a new symmetric state. The higher presence of the symmetric state can be considered as a symmetrization of the wake bi-stability with an increasing Re. The wake symmetry under high Re attributed to the highly frequent switches of the wake is extremely sensitive to small yaw angles, showing the feature of bi-stable flows. The wake asymmetry is confirmed in numerical simulations with both low and high Re. The wake asymmetries are indicated by the wake separation, the reattachment and the wake dynamics identified by the proper orthogonal decomposition. However, the turbulence level is found to be significantly higher with a higher Re. This leads to a higher possibility to break the asymmetric state, resulting in highly frequent switches showing symmetry
Impact of the bogies and cavities on the aerodynamic behaviour of a high-speed train. An IDDES study
No full textThis study investigates the effects of bogie cavities and bogies on the aerodynamic behaviour of a high-speed train (HST) using improved delayed detached eddy simulation (IDDES) at Re = 3.3
7 105. The main aim of this work is to identify the individual influence of bogies and cavities on the surrounding flow, thereby revealing aspects to further improve the HST aerodynamic performance. The accuracy of the numerical method has been validated against the experimental data obtained from a previous reduced-scale moving-model test, a wind tunnel test and a full-scale field test. The underbody flow, wake flow, slipstream velocity, aerodynamic drag and the computational costs are compared for three cases. The results show that installing the bogies around the cavities in Case 1 and sealing the cavities in Case 3 can effectively reduce the turbulence kinetic energy (TKE) and slipstream velocity around the HST. The cavities in Case 2 produce the highest level of TKE and slipstream velocity distribution in both underbody flow region and the wake region, compared to other two cases. This presents the largest scales of the shear vortices in the cavities and longitudinal vortices in the wake. Compared to Case 2, the TSI values of the slipstream velocity at the trackside position decreases by about 18.9% in Case 1 and 56.9% in Case 3, respectively. The cavities account for approximately 65% of the aerodynamic drag of the HST. Installing bogies in Case 1 and sealing cavities in Case 3 gives a 24% and 56% drag reduction for the overall HST. It is recommended to invest 10% higher resources to achieve an accurate surrounding flow prediction of a HST in presence of bogies
Active wake-flow control for a notchback Ahmed body driven by a genetically inspired optimization
No full textThis paper explores active wake-flow control on a notchback Ahmed body using genetically inspired optimization. Hotwire and particle image velocimetry measurements record velocity data and flow structures in the wake. Pulsed jets at four actuation slots (two at the roof trailing edge, two at the side trailing edges) dynamically control the wake to minimize aerodynamic drag. The study achieves up to 9.2% (without consideration of energy consumption) drag reduction, primarily by manipulating vortices from the roof rear end. The paper elucidates the underlying flow mechanism and evaluates various actuation strategies, highlighting how optimal control leads to reattachment of wake separation at the rear slant, diminishing the slant bubble and promoting downstream reattachment for enhanced drag reduction
Influence of the rounded rear edge on wake bi-stability of a notchback bluff body
No full textThe wake bi-stability behind notchback Ahmed bodies is investigated by performing wind tunnel experiments and large eddy simulations (LESs). The focus of this study is on the suppression of bi-stable wakes achieved by rounding the roof\u27s trailing edge of the body. The suppression effect is found to depend on the Reynolds number (R e). The wake behind a sharp edge remains bi-stable for all tested R e. However, for a rounded edge with small radius, wake bi-stability at R e = 0.5
7 10 5 and wake symmetrization with 0.75
7 10 5 ≤ R e ≤ 1.5
7 10 5 are observed. Increasing R e with R e ≥ 1.75
7 10 5, the wake returns to the bi-stable state. Particularly, with R e ≥ 2
7 10 5, a stable asymmetric wake state with no switches is observed for long periods. Performing LES confirms the expected wake asymmetry at R e = 0.5
7 10 5 and symmetry at R e = 1
7 10 5 for the case of rounded edge with a small radius. Besides, another wake symmetry is observed for the rounded edge with a large radius at R e = 0.5
7 10 5. For the two wake symmetries shown in the LES results, the symmetrization is attributed to wake suppression in the notchback region, forcing the flow separation from the rear roof to attach to the slant on both sides of the body
Blockage influence on bi-stable flows of a notchback bluff body
No full textThe expected flow asymmetry behind a three-dimensional notchback Ahmed body is numerically investigated using large-eddy simulations with different blockage ratios of 0%, 5 %, 10 %, and 20 %. The focus of the study is on the natural bi-stable flow influenced by the blockage ratio. Although the wake asymmetry can be observed under the blockage ratio within 0 % - 10 %, the significant blockage influence on the sensitive bi-stability is indicated by the wake structures, pressure gradients, and wake dynamics achieved with the proper orthogonal decomposition. The higher blockage ratio increases the turbulence kinetic energy, velocity, and negative pressure in the near-wake region, resulting in the decrease in the asymmetry degree. The consistency of the asymmetric wake is found with blockage ratios between 0% and 5 %. However, a 20 % blockage ratio symmetrizes the bi-stable wake. Several existing drag corrections for the blockage influence are discussed. The wind tunnel experiment verifies the bi-stable flow with low blockage ratios and the wake symmetrization with a 20 % blockage ratio
He Yimen xian sheng ji
No full text吳蔭培校刊 ; 韓崇[等]輯.框17.9x13公分, 10行23字, 白口, 四周雙邊, 單黑魚尾, 版心上鐫題名, 中鐫卷次, 下鐫葉次.內封背頁牌記題"宣統元年己酉秋平江吳氏刊於廣州"卷末附"義門弟子姓氏錄"Wu Yinpei jiao kan ; Han Chong [deng] ji.Kuang 17.9x13 gong fen, 10 hang 23 zi, bai kou, si zhou shuang bian, dan hei yu wei, ban xin shang juan ti ming, zhong juan juan ci, xia juan ye ci.Nei feng bei ye pai ji ti "Xuantong yuan nian ji you qiu Ping Jiang Wu shi kan yu Guangzhou"Juan mo fu "Yimen di zi xing shi lu
Protecting Animals 36: Author Witi Ihimaera
No full textIn this very special episode of Knowing Animals I am joined by beloved New Zealand author Witi Ihimaera. Witi has written many books featuring nonhuman animals. He offers us a non-colonial lens through which to think about the human/nonhuman relationship
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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