{"id":250251,"date":"2025-03-09T19:23:14","date_gmt":"2025-03-09T19:23:14","guid":{"rendered":"https:\/\/mecheng.iisc.ac.in\/fpl\/?p=250251"},"modified":"2025-03-09T19:27:20","modified_gmt":"2025-03-09T19:27:20","slug":"bubbly-turbulent-flow","status":"publish","type":"post","link":"https:\/\/mecheng.iisc.ac.in\/fpl\/bubbly-turbulent-flow\/","title":{"rendered":"Bubbly Turbulent Flow"},"content":{"rendered":"\n<p>There has been a lot of recent interest in reducing drag on surfaces using bubbles with potential applications ranging from drag reduction of underwater vehicles to pressure drop reduction in liquid pipelines. This includes primarily two broad methods, one utilizing \u201ctextured hydrophobic\u201d surfaces, and the other more classical approach is to inject small bubbles from the surface into the flow. We have done work related to both approaches as detailed below.<\/p>\n\n\n\n<p><\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>1. Bubble injection into the flow<\/strong><\/h2>\n\n\n\n<p><\/p>\n\n\n<div class=\"foogallery foogallery-container foogallery-carousel foogallery-lightbox-none fg-carousel-hide-nav-arrows fg-carousel-hide-progress-bar fg-carousel fg-light fg-border-thin fg-round-large fg-shadow-medium fg-loading-default fg-loaded-fade-in fg-caption-always fg-hover-fade fg-transparent-overlays fg-ready\" id=\"foogallery-gallery-250243\" data-foogallery=\"{&quot;item&quot;:{&quot;showCaptionTitle&quot;:false,&quot;showCaptionDescription&quot;:true},&quot;lazy&quot;:true,&quot;template&quot;:{&quot;maxItems&quot;:1,&quot;scale&quot;:0.12,&quot;gutter&quot;:{&quot;min&quot;:-40,&quot;max&quot;:-20,&quot;unit&quot;:&quot;%&quot;},&quot;autoplay&quot;:{&quot;time&quot;:5,&quot;interaction&quot;:&quot;pause&quot;},&quot;centerOnClick&quot;:true}}\" >\n\t<button type=\"button\" class=\"fg-carousel-prev\"><\/button>\n\t<div class=\"fg-carousel-inner\">\n\t\t<div class=\"fg-carousel-center\"><\/div>\n\t\t<div class=\"fg-item fg-type-image fg-idle\"><figure class=\"fg-item-inner\"><a data-caption-desc=\"Ring-bubble (top-view): Idealization of bubbly turbulent flows: Interactions of a single air bubble with a vortex ring in water (top-view)\" data-attachment-id=\"250244\" data-type=\"image\" class=\"fg-thumb\"><span class=\"fg-image-wrap\"><img fetchpriority=\"high\" decoding=\"async\" width=\"1000\" height=\"667\" class=\"skip-lazy fg-image\" data-src-fg=\"https:\/\/mecheng.iisc.ac.in\/fpl\/wp-content\/uploads\/cache\/2025\/03\/Bubbly-Turbulent-Flow-1\/2844606038.png\" src=\"data:image\/svg+xml,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20width%3D%221000%22%20height%3D%22667%22%20viewBox%3D%220%200%201000%20667%22%3E%3C%2Fsvg%3E\" loading=\"eager\"><\/span><span class=\"fg-image-overlay\"><\/span><\/a><figcaption class=\"fg-caption\"><div class=\"fg-caption-inner\"><div class=\"fg-caption-desc\">Ring-bubble (top-view): Idealization of bubbly turbulent flows: Interactions of a single air bubble with a vortex ring in water (top-view)<\/div><\/div><\/figcaption><\/figure><div class=\"fg-loader\"><\/div><\/div><div class=\"fg-item fg-type-image fg-idle\"><figure class=\"fg-item-inner\"><a data-caption-desc=\"Ring-bubble (side-view): Idealization of bubbly turbulent flows: Interactions of a single air bubble with a vortex ring in water (side-view)\" data-attachment-id=\"250245\" data-type=\"image\" class=\"fg-thumb\"><span class=\"fg-image-wrap\"><img decoding=\"async\" width=\"1000\" height=\"667\" class=\"skip-lazy fg-image\" data-src-fg=\"https:\/\/mecheng.iisc.ac.in\/fpl\/wp-content\/uploads\/cache\/2025\/03\/Bubbly-Turbulent-Flow-2\/3065600530.png\" src=\"data:image\/svg+xml,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20width%3D%221000%22%20height%3D%22667%22%20viewBox%3D%220%200%201000%20667%22%3E%3C%2Fsvg%3E\" loading=\"eager\"><\/span><span class=\"fg-image-overlay\"><\/span><\/a><figcaption class=\"fg-caption\"><div class=\"fg-caption-inner\"><div class=\"fg-caption-desc\">Ring-bubble (side-view): Idealization of bubbly turbulent flows: Interactions of a single air bubble with a vortex ring in water (side-view)<\/div><\/div><\/figcaption><\/figure><div class=\"fg-loader\"><\/div><\/div><div class=\"fg-item fg-type-image fg-idle\"><figure class=\"fg-item-inner\"><a data-caption-desc=\"Bubbly turbulent flow: Bubble injection into a turbulent channel flow for drag reduction\" data-attachment-id=\"250246\" data-type=\"image\" class=\"fg-thumb\"><span class=\"fg-image-wrap\"><img decoding=\"async\" width=\"1000\" height=\"667\" class=\"skip-lazy fg-image\" data-src-fg=\"https:\/\/mecheng.iisc.ac.in\/fpl\/wp-content\/uploads\/cache\/2025\/03\/Bubbly-Turbulent-Flow-3\/93262062.png\" src=\"data:image\/svg+xml,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20width%3D%221000%22%20height%3D%22667%22%20viewBox%3D%220%200%201000%20667%22%3E%3C%2Fsvg%3E\" loading=\"eager\"><\/span><span class=\"fg-image-overlay\"><\/span><\/a><figcaption class=\"fg-caption\"><div class=\"fg-caption-inner\"><div class=\"fg-caption-desc\">Bubbly turbulent flow: Bubble injection into a turbulent channel flow for drag reduction<\/div><\/div><\/figcaption><\/figure><div class=\"fg-loader\"><\/div><\/div><div class=\"fg-item fg-type-image fg-idle\"><figure class=\"fg-item-inner\"><a data-caption-desc=\"Top wall air injection into channel: Air layer formation near the wall\" data-attachment-id=\"250247\" data-type=\"image\" class=\"fg-thumb\"><span class=\"fg-image-wrap\"><img decoding=\"async\" width=\"1000\" height=\"667\" class=\"skip-lazy fg-image\" data-src-fg=\"https:\/\/mecheng.iisc.ac.in\/fpl\/wp-content\/uploads\/cache\/2025\/03\/Bubbly-Turbulent-Flow-4\/2467373590.png\" src=\"data:image\/svg+xml,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20width%3D%221000%22%20height%3D%22667%22%20viewBox%3D%220%200%201000%20667%22%3E%3C%2Fsvg%3E\" loading=\"eager\"><\/span><span class=\"fg-image-overlay\"><\/span><\/a><figcaption class=\"fg-caption\"><div class=\"fg-caption-inner\"><div class=\"fg-caption-desc\">Top wall air injection into channel: Air layer formation near the wall<\/div><\/div><\/figcaption><\/figure><div class=\"fg-loader\"><\/div><\/div>\t<\/div>\n\t<div class=\"fg-carousel-bottom\"><\/div>\n\t<div class=\"fg-carousel-progress\"><\/div>\n\t<button type=\"button\" class=\"fg-carousel-next\"><\/button>\n<\/div><style type=\"text\/css\">.fg-caption-desc{\r\ncolor: #1a1a1a;\r\ntext-align:center;\r\npadding-bottom: 40px;\r\n}<\/style>\n\n\n<p><\/p>\n\n\n\n<p>In the approach using injected bubbles into the flow, drag reduction by bubbles can either be caused by direct modification of fluid properties like density and viscosity, or through the relatively more complex interaction of bubbles with turbulent structures within the boundary layer. <\/p>\n\n\n\n<p>In this broad area, we have studied:<\/p>\n\n\n\n<ol style=\"list-style-type:lower-roman\" class=\"wp-block-list\">\n<li>Single bubble \u2013 Vortex ring studies: An idealization of the interaction of bubbles with turbulent structures is the interaction of a single bubble with a single vortical structure, namely a vortex ring (formed in water). In these studies, measurements of both the bubble dynamics and vorticity dynamics have been done to help understand the two-way coupled problem over a large range of vortex ring and bubble parameters. The results from these studies show that they exhibit many phenomena also seen in bubbly turbulent flows such as reduction in enstrophy, suppression of structures, enhancement of energy at small scales and reduction in energy at large scales. These similarities suggest that results from the present experiments can be helpful in better understanding interactions of bubbles with eddies in turbulent flows.<\/li>\n\n\n\n<li>Drag reduction using bubbles in turbulent channel: We have also studied actual drag reduction in a turbulent channel flow by the injection of bubbles. We have systematically mapped out the effect of different rates of bubble injection, on the drag reduction (pressure drop) achieved within a turbulent channel. These results show that there exist many different regimes of bubble dynamics in the flow depending on the rate of bubble injection and the channel Reynolds numbers. The measured drag (or pressure drop) is found to be greatly dependent on the bubble dynamics regime with possibilities of both enhanced drag and reduced drag compared to the reference no bubble case. When the conditions are right, very large drag reductions of up to 60 % were achieved.<\/li>\n<\/ol>\n\n\n\n<p><\/p>\n\n\n\n<h2 class=\"wp-block-heading\">2. <strong>Trapped bubbles on the surface \u2013 Superhydrophobic surfaces:<\/strong><\/h2>\n\n\n\n<p><\/p>\n\n\n<div class=\"foogallery foogallery-container foogallery-carousel foogallery-lightbox-none fg-carousel-hide-nav-arrows fg-carousel-hide-progress-bar fg-carousel fg-light fg-border-thin fg-round-large fg-shadow-medium fg-loading-default fg-loaded-fade-in fg-caption-always fg-hover-fade fg-transparent-overlays fg-ready\" id=\"foogallery-gallery-250250\" data-foogallery=\"{&quot;item&quot;:{&quot;showCaptionTitle&quot;:false,&quot;showCaptionDescription&quot;:true},&quot;lazy&quot;:true,&quot;template&quot;:{&quot;maxItems&quot;:1,&quot;scale&quot;:0.12,&quot;gutter&quot;:{&quot;min&quot;:-40,&quot;max&quot;:-20,&quot;unit&quot;:&quot;%&quot;},&quot;autoplay&quot;:{&quot;time&quot;:5,&quot;interaction&quot;:&quot;pause&quot;},&quot;centerOnClick&quot;:true}}\" >\n\t<button type=\"button\" class=\"fg-carousel-prev\"><\/button>\n\t<div class=\"fg-carousel-inner\">\n\t\t<div class=\"fg-carousel-center\"><\/div>\n\t\t<div class=\"fg-item fg-type-image fg-idle\"><figure class=\"fg-item-inner\"><a data-caption-desc=\"Trapped bubbles on the surface Textured superhydrophobic surfaces: Trapping air on the surface for drag reduction\" data-attachment-id=\"250248\" data-type=\"image\" class=\"fg-thumb\"><span class=\"fg-image-wrap\"><img decoding=\"async\" width=\"1000\" height=\"667\" class=\"skip-lazy fg-image\" data-src-fg=\"https:\/\/mecheng.iisc.ac.in\/fpl\/wp-content\/uploads\/cache\/2025\/03\/Bubbly-Turbulent-Flow-5\/2967510026.png\" src=\"data:image\/svg+xml,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20width%3D%221000%22%20height%3D%22667%22%20viewBox%3D%220%200%201000%20667%22%3E%3C%2Fsvg%3E\" loading=\"eager\"><\/span><span class=\"fg-image-overlay\"><\/span><\/a><figcaption class=\"fg-caption\"><div class=\"fg-caption-inner\"><div class=\"fg-caption-desc\">Trapped bubbles on the surface Textured superhydrophobic surfaces: Trapping air on the surface for drag reduction<\/div><\/div><\/figcaption><\/figure><div class=\"fg-loader\"><\/div><\/div><div class=\"fg-item fg-type-image fg-idle\"><figure class=\"fg-item-inner\"><a data-caption-desc=\"Towards sustaining underwater Cassie state of wetting: Controlling the solubility of air in water through changes in the absolute pressure\" data-attachment-id=\"250249\" data-type=\"image\" class=\"fg-thumb\"><span class=\"fg-image-wrap\"><img decoding=\"async\" width=\"1000\" height=\"667\" class=\"skip-lazy fg-image\" data-src-fg=\"https:\/\/mecheng.iisc.ac.in\/fpl\/wp-content\/uploads\/cache\/2025\/03\/Bubbly-Turbulent-Flow-6\/1868103806.png\" src=\"data:image\/svg+xml,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20width%3D%221000%22%20height%3D%22667%22%20viewBox%3D%220%200%201000%20667%22%3E%3C%2Fsvg%3E\" loading=\"eager\"><\/span><span class=\"fg-image-overlay\"><\/span><\/a><figcaption class=\"fg-caption\"><div class=\"fg-caption-inner\"><div class=\"fg-caption-desc\">Towards sustaining underwater Cassie state of wetting: Controlling the solubility of air in water through changes in the absolute pressure<\/div><\/div><\/figcaption><\/figure><div class=\"fg-loader\"><\/div><\/div>\t<\/div>\n\t<div class=\"fg-carousel-bottom\"><\/div>\n\t<div class=\"fg-carousel-progress\"><\/div>\n\t<button type=\"button\" class=\"fg-carousel-next\"><\/button>\n<\/div><style type=\"text\/css\">.fg-caption-desc{\r\ncolor: #1a1a1a;\r\ntext-align:center;\r\npadding-bottom: 40px;\r\n}<\/style>\n\n\n<p><\/p>\n\n\n\n<p>In contrast to the injection of bubbles, another mechanism for drag reduction is the use of \u201ctextured hydrophobic surfaces\u201d as channel walls. The ability of these surfaces to provide substantial drag reduction has been attributed to the presence of air bubbles trapped on the surface cavities. However, this drag reduction cannot be sustained due to gradual dissolution of trapped air into water. In our recent work, we have explored the possibility of sustaining the underwater Cassie state of wetting in a microchannel by controlling the solubility of air in water; the solubility being changed by controlling the local absolute pressure near the surface. We show that using this method, we can in fact make the water locally supersaturated with air thus encouraging the growth of trapped air pockets on the surface. In this case, the water acts as a pumping medium, delivering air to the crevices of the hydrophobic surface in the microchannel, where the presence of air pockets is most beneficial from the drag reduction perspective.<\/p>\n\n\n\n<p><\/p>\n","protected":false},"excerpt":{"rendered":"<p>There has been a lot of recent interest in reducing drag on surfaces using bubbles with potential applications ranging from drag reduction of underwater vehicles to pressure drop reduction in liquid pipelines. This includes primarily two broad methods, one utilizing \u201ctextured hydrophobic\u201d surfaces, and the other more classical approach is to inject small bubbles from [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","inline_featured_image":false,"footnotes":""},"categories":[1],"tags":[],"class_list":["post-250251","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/mecheng.iisc.ac.in\/fpl\/wp-json\/wp\/v2\/posts\/250251","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/mecheng.iisc.ac.in\/fpl\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mecheng.iisc.ac.in\/fpl\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mecheng.iisc.ac.in\/fpl\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/mecheng.iisc.ac.in\/fpl\/wp-json\/wp\/v2\/comments?post=250251"}],"version-history":[{"count":1,"href":"https:\/\/mecheng.iisc.ac.in\/fpl\/wp-json\/wp\/v2\/posts\/250251\/revisions"}],"predecessor-version":[{"id":250252,"href":"https:\/\/mecheng.iisc.ac.in\/fpl\/wp-json\/wp\/v2\/posts\/250251\/revisions\/250252"}],"wp:attachment":[{"href":"https:\/\/mecheng.iisc.ac.in\/fpl\/wp-json\/wp\/v2\/media?parent=250251"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mecheng.iisc.ac.in\/fpl\/wp-json\/wp\/v2\/categories?post=250251"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mecheng.iisc.ac.in\/fpl\/wp-json\/wp\/v2\/tags?post=250251"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}