{"id":557420,"date":"2024-11-05T18:17:58","date_gmt":"2024-11-05T18:17:58","guid":{"rendered":"https:\/\/pdfstandards.shop\/product\/uncategorized\/esdu-080122009\/"},"modified":"2024-11-05T18:17:58","modified_gmt":"2024-11-05T18:17:58","slug":"esdu-080122009","status":"publish","type":"product","link":"https:\/\/pdfstandards.shop\/product\/publishers\/esdu\/esdu-080122009\/","title":{"rendered":"ESDU 08012:2009"},"content":{"rendered":"

INTRODUCTION<\/strong><\/p>\n

This Data Item is the second in the series of four Items (Parts
\nIIIA to IIID) comprising Part III of the wider five-part series
\n(Parts I to V) dealing with the aerodynamics and aero-acoustics of
\nrectangular planform cavities, see Section 2.2 in Part I (Reference
\n108). The general subject area of Part III is the alleviation of
\nunsteady flow effects and is introduced in Part IIIA (Reference
\n110). The present Data Item (Part IIIB) deals with acoustic
\nsuppression using passive devices. The use of active devices is
\nconsidered in Part IIIC (Reference 111), while the alleviation of
\nstore deployment conditions is dealt with in Part IIID (Reference
\n112).<\/p>\n

The very wide range of passive devices employed in both
\nwind-tunnel and flight tests can be separated into seven main
\ntypes. In the discussion of the various types tested, even the less
\nsuccessful ones are mentioned, since ineffectiveness in one
\nsituation should not be taken to imply ineffectiveness in all
\nsituations – although that may be true of some. In this Item the
\nparticular types of passive device (or actuator*) covered are
\nfences or spoilers (Section 3), vortex generators (Section 4),
\nfront and\/or rear wall geometry changes (Section 5), the
\nrod-in-crossflow (Section 6), passive resonance tubes (Section 7),
\nHelmholtz resonators (Section 8), and baffles and absorptive
\nmaterials (Section 9). The work is prefaced, in Section 2.1, by a
\nconsideration of the various means whereby passive devices affect
\nthe cavity shear flow. The first four device types, on which a
\nconsiderable amount of research has been carried out, are tackled
\nin Sections 3 to 6 in a common fashion involving firstly a
\nhistorical overview of the research, secondly an assessment of the
\neffectiveness of the device in terms of acoustic suppression, and
\nthirdly whatever can be said concerning the drag of the combined
\ncavity-plus-device compared to the cavity baseline drag,
\ni.e.<\/i> the drag of the cavity without the device. Cavity
\nbaseline drag (gross drag), and its relationship with the drag (net
\ndrag) predicted using ESDU 00006 (Reference 106) for closed flow
\nand ESDU 00007 (Reference 107) for open and transitional flows, is
\noutlined in Section 6.2 of Part IIIA (Reference 110). Each of
\nSections 3 to 6 contains a list of overall conclusions concerning
\nthe device under consideration. The final three device types,
\nconsidered in Sections 7 to 9, have had relatively little research
\nattention compared to the first four, and so are dealt with in a
\nmore general way, with conclusions being given where possible.<\/p>\n

Section 10 contains the overriding conclusions concerning the
\nuse of each passive device and may be consulted prior to a
\nconsideration of the reviews of device performance and the fuller
\nconclusions set out in Sections 3 to 9. In summary, carefully
\ndesigned spoilers and rear wall ramps have been found to be
\nsuccessful cavity noise suppression devices at subsonic speeds, and
\nsatisfactory at low supersonic speeds, as evidenced by their
\nwidespread past and present use on military aircraft. The newer
\nrod-in-crossflow concept shows considerable promise in modal and
\nbackground noise alleviation over a wide Mach number range. Of the
\nother devices, the small amount of available data suggests that
\nrearward-facing steps ahead of the front wall, vortex generators,
\nHelmholtz resonators and acoustic liners could be successful in
\nappropriate situations, or perhaps in combination with another
\ndevice. The particular question of the intrinsic drag of the
\nvarious devices and the overall drag of a cavity before and,
\nespecially, after suppression requires more research.<\/p>\n

Finally, the inclusion of the rod-in-crossflow in the device
\ntypes considered, being a high frequency (HF) suppression device,
\nrequired more information on the physical processes involved, and
\nAppendices A and B outline those processes, while Appendix C
\nconsiders the characteristic signature of effective (and
\nineffective) HF devices.<\/p>\n

* It might reasonably be thought that an actuator would be
\ncapable of some form of actuation other than deployment. However,
\nin the literature the term "actuator" is commonly used for any
\ndevice, whether active or passive.<\/p>\n","protected":false},"excerpt":{"rendered":"

Aerodynamics and Aero-Acoustics of Rectangular Planform Cavities – Part IIIB: Alleviation of Unsteady Flow Effects – Acoustic Suppression Using Passive Devices<\/b><\/p>\n\n\n\n\n
Published By<\/td>\nPublication Date<\/td>\nNumber of Pages<\/td>\n<\/tr>\n
ESDU<\/b><\/a><\/td>\n2009-06-01<\/td>\n174<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n","protected":false},"featured_media":557427,"template":"","meta":{"rank_math_lock_modified_date":false,"ep_exclude_from_search":false},"product_cat":[2675],"product_tag":[],"class_list":{"0":"post-557420","1":"product","2":"type-product","3":"status-publish","4":"has-post-thumbnail","6":"product_cat-esdu","8":"first","9":"instock","10":"sold-individually","11":"shipping-taxable","12":"purchasable","13":"product-type-simple"},"_links":{"self":[{"href":"https:\/\/pdfstandards.shop\/wp-json\/wp\/v2\/product\/557420","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pdfstandards.shop\/wp-json\/wp\/v2\/product"}],"about":[{"href":"https:\/\/pdfstandards.shop\/wp-json\/wp\/v2\/types\/product"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/pdfstandards.shop\/wp-json\/wp\/v2\/media\/557427"}],"wp:attachment":[{"href":"https:\/\/pdfstandards.shop\/wp-json\/wp\/v2\/media?parent=557420"}],"wp:term":[{"taxonomy":"product_cat","embeddable":true,"href":"https:\/\/pdfstandards.shop\/wp-json\/wp\/v2\/product_cat?post=557420"},{"taxonomy":"product_tag","embeddable":true,"href":"https:\/\/pdfstandards.shop\/wp-json\/wp\/v2\/product_tag?post=557420"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}