{"id":8459,"date":"2024-06-01T16:01:28","date_gmt":"2024-06-01T08:01:28","guid":{"rendered":"https:\/\/tommykwan.com\/blog\/?p=8459"},"modified":"2024-06-01T16:52:08","modified_gmt":"2024-06-01T08:52:08","slug":"why-turbofan-engine-needs-high-bypass-ratio-%e9%bb%9e%e8%a7%a3%e8%a6%81high-bypass-ratio","status":"publish","type":"post","link":"https:\/\/tommykwan.com\/blog\/aviation\/why-turbofan-engine-needs-high-bypass-ratio-%e9%bb%9e%e8%a7%a3%e8%a6%81high-bypass-ratio\/","title":{"rendered":"Why turbofan engine needs High bypass ratio? \u9ede\u89e3\u8981high bypass ratio?"},"content":{"rendered":"<p style=\"text-align: center;\"><span style=\"color: #ff0000;\"><strong>Force = mass x acceleration<\/strong><\/span><\/p>\n[Ref <a href=\"https:\/\/skybrary.aero\/articles\/turbofan-engine\">Turbofan Engine | SKYbrary Aviation Safety<\/a>]\n<p>High bypass engines usually have a single stage fan which generates a high volume but relatively low speed air stream. The <strong>fan airflow<\/strong>, referred to as the<strong> cold air stream<\/strong>, is accelerated by the fan and passes through the engine<strong> remaining outside of the engine core<\/strong>. The cold air stream moves much slower than the hot stream gas flow passing through the engine core. The cold stream serves to help cool the engine core and is then mixed with the hot stream exhaust to decrease both the temperature and the speed of the jet core exhaust flow. This speed reduction serves to both <strong>reduce the noise<\/strong> generated by the engine and to <strong>increase<\/strong> the engine <strong>efficiency<\/strong> by more closely matching the speed of the exhaust flow to the design speed of the aircraft.<\/p>\n<div class=\"embed-container\"><iframe loading=\"lazy\" title=\"How a High Bypass Turbofan Works\" width=\"1170\" height=\"878\" src=\"https:\/\/www.youtube.com\/embed\/xADjIAqJigI?feature=oembed\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share\" referrerpolicy=\"strict-origin-when-cross-origin\" allowfullscreen><\/iframe><\/div>\n<p>&nbsp;<\/p>\n<p><span style=\"text-decoration: underline;\">What&#8217;s bypass ratio (by-pass ratio)?<br \/>\n[Ref. <a href=\"https:\/\/www.grc.nasa.gov\/www\/k-12\/airplane\/aturbf.html\">Turbofan Engine (nasa.gov)<\/a>]\n<\/span><\/p>\n<p>The <b>bypass ratio<\/b> is the ratio of the air that goes around the engine to the air that goes through the core.<\/p>\n<p>&nbsp;<\/p>\n<p><span style=\"text-decoration: underline;\">Why high bypass ratio better?<br \/>\n<a href=\"https:\/\/www.grc.nasa.gov\/www\/k-12\/airplane\/turbfan.html\">[Ref. Turbofan Thrust (nasa.gov)<\/a>, <a href=\"https:\/\/www1.grc.nasa.gov\/beginners-guide-to-aeronautics\/thrust-force\/\">Thrust Equation | Glenn Research Center | NASA<\/a>]<\/span><\/p>\n<p>To move an\u00a0<a href=\"https:\/\/www.grc.nasa.gov\/www\/k-12\/airplane\/airplane.html\">airplane<\/a>\u00a0through the air,\u00a0<a href=\"https:\/\/www.grc.nasa.gov\/www\/k-12\/airplane\/thrust1.html\">thrust<\/a>\u00a0is generated by some kind of\u00a0<a href=\"https:\/\/www.grc.nasa.gov\/www\/k-12\/airplane\/bgp.html\">propulsion system<\/a>. Most modern airliners use\u00a0<a href=\"https:\/\/www.grc.nasa.gov\/www\/k-12\/airplane\/aturbf.html\">turbofan engines<\/a>\u00a0because of their high thrust and good\u00a0<a href=\"https:\/\/www.grc.nasa.gov\/www\/k-12\/airplane\/sfc.html\">fuel efficiency.<\/a><\/p>\n<p>There are<strong> two possible ways to produce high thrust<\/strong>. One way is to <strong>make the engine flow rate<\/strong> (m dot) <strong>as high as possible<\/strong>. As long as the exit velocity is greater than the free stream, entrance velocity, a high engine flow will produce high thrust. This is the design theory behind propeller aircraft and high-bypass turbofan engines. A large amount of air is processed each second, but the velocity is not changed very much. The <strong>other way to produce high thrust is to make the exit velocity very much greater than the incoming velocity<\/strong>. This is the design theory behind pure turbojets, turbojets with afterburners, and rockets. A moderate amount of flow is accelerated to a high velocity in these engines. If the exit velocity becomes very high, there are other physical processes which become important and affect the efficiency of the engine. These effects are described in detail on other pages at this site.<\/p>\n<p id=\"gas-turbine-engine\"><strong>High bypass gas Turbine<\/strong> <strong>Engine<\/strong> is literally <strong>make a balance and take the advantage of two extreme approach<\/strong> in application.<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p><a href=\"https:\/\/tommykwan.com\/blog\/aviation\/hot-topic-turbofan-engine\/\">Hot topic : Turbofan Engine \u2013 Tommy&#8217;s Diaries (tommykwan.com)<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Force = mass x acceleration [Ref Turbofan Engine | SKYbrary Aviation Safety] High bypass engines usually have a single stage fan which generates a high volume but relatively low speed air stream. The fan airflow, referred to as the cold air stream, is accelerated by the fan and passes through the engine remaining outside of<a class=\"read-more \" href=\"https:\/\/tommykwan.com\/blog\/aviation\/why-turbofan-engine-needs-high-bypass-ratio-%e9%bb%9e%e8%a7%a3%e8%a6%81high-bypass-ratio\/\" title=\"Read More\"> <span class=\"button default\">Read More<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[75,68,64],"tags":[],"class_list":["post-8459","post","type-post","status-publish","format-standard","hentry","category-agk-airframe-engine-system","category-atpl-knowledge","category-aviation"],"_links":{"self":[{"href":"https:\/\/tommykwan.com\/blog\/wp-json\/wp\/v2\/posts\/8459","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/tommykwan.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/tommykwan.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/tommykwan.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/tommykwan.com\/blog\/wp-json\/wp\/v2\/comments?post=8459"}],"version-history":[{"count":14,"href":"https:\/\/tommykwan.com\/blog\/wp-json\/wp\/v2\/posts\/8459\/revisions"}],"predecessor-version":[{"id":8478,"href":"https:\/\/tommykwan.com\/blog\/wp-json\/wp\/v2\/posts\/8459\/revisions\/8478"}],"wp:attachment":[{"href":"https:\/\/tommykwan.com\/blog\/wp-json\/wp\/v2\/media?parent=8459"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/tommykwan.com\/blog\/wp-json\/wp\/v2\/categories?post=8459"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/tommykwan.com\/blog\/wp-json\/wp\/v2\/tags?post=8459"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}