{"id":557325,"date":"2024-11-05T18:17:40","date_gmt":"2024-11-05T18:17:40","guid":{"rendered":"https:\/\/pdfstandards.shop\/product\/uncategorized\/esdu-040232009\/"},"modified":"2024-11-05T18:17:40","modified_gmt":"2024-11-05T18:17:40","slug":"esdu-040232009","status":"publish","type":"product","link":"https:\/\/pdfstandards.shop\/product\/publishers\/esdu\/esdu-040232009\/","title":{"rendered":"ESDU 04023:2009"},"content":{"rendered":"

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

Background<\/strong><\/p>\n

The effects of flow instabilities on the liquid or gas within an
\nenclosed volume with an aperture open to a static or moving
\nexternal flow, or related matters, have been studied for at least
\nthe last 150 years. For example, Sondhaus in 1854 (Reference 1),
\nstudied the effects of a jet impinging upon an edge, producing an
\nacoustic effect known as an edge tone<\/i>, associated with the
\nproduction of sound in organ pipes and other musical instruments.
\nTyndall, in 1867 (Reference 2), studied the effect that sound had
\non the stability of jets, while in 1868 Helmholtz published
\n(Reference 3) the results of, among other things, his analysis of
\nthe natural frequency of an enclosed volume with a small aperture,
\nsubsequently called a Helmholtz resonator<\/i>. Later, in 1877,
\nLord Rayleigh (John William Strutt) published (Reference 4) a
\nwidely used book on the theory of sound, including the effects of
\nsound on the stability of vortex sheets and the development of a
\ntheory for the resonant conditions of an open-ended pipe. Much of
\nthe work in References 1 to 4 has provided a foundation for the
\nsubsequent development of the various theories associated with
\ncavity aerodynamics and aero-acoustics.<\/p>\n

The study of cavity acoustics in general, and jet impingement in
\nrelation to edge tones in particular, continued at a steady pace
\nfor the next 70 years, with various applications. However, in the
\nlate 1940s and early 1950s a particular problem in the aircraft
\nindustry spurred the accelerating growth of research into cavity
\naerodynamics, and especially acoustics, that has occurred over the
\nlast 50 years. At that time there was an increasing awareness of
\nthe effects that the oscillation of the airflow in and around open
\ncavities such as wheel wells and bomb bays were having on the
\naerodynamics, and even the structural integrity* of such cavities
\nand their contents. Early work in this area was carried out in
\nrelation to the bomb bays of the English Electric Canberra
\n(References 6, 8, 9, 13, 19, 21, 29 and 39) and Boeing B47
\n(Reference 10). At the same time as this work on specific aircraft
\nwas being carried out in the 1950s and 1960s, a number of
\ninvestigations, mainly wind tunnel and flight tests, involving more
\ngeneral research into the unsteady aerodynamics and noise due to
\ncavities were also under way (for example, References 7, 11, 14 to
\n18, 20, 22 to 28 and 30 to 38). All these areas of research
\nprovided a firm basis for the rapidly expanding work, both
\nexperimental and theoretical, including computational fluid
\ndynamics (CFD), from the 1970s onwards.<\/p>\n

Although nearly all the research on the unsteady aerodynamics
\nand acoustics of cavities has been in relation to weapons bays,
\nmuch of the resulting information could also be applied to
\nundercarriage bays or wheel wells. However, in that application
\nthere is usually less of a problem due to the unsteadiness and
\nnoise arising from the flow within such cavities (although drag is
\nobviously a concern), and more of a problem in relation to the
\nfar-field noise generated by the wheel bay and the extended
\nundercarriage unit (for example, References 44, 48, 49, 51 and 68).
\nSuch considerations are outside the scope of this Data Item and are
\nmore relevant to the work of the ESDU Noise Committee, see ESDU
\n90023 (Reference 95) for example.<\/p>\n

The main problems involving the use of rectangular planform
\ncavities for weapons carriage are twofold.<\/p>\n

(a) Flow unsteadiness and the possibility of self-sustained
\noscillations and the likelihood of acoustic phenomena for deep to
\nmoderately deep cavities with open<\/i> or
\ntransitional<\/i> flow (see ESDU 00007 \u2013 Reference 97).<\/p>\n

(b) Weapon release difficulties from shallow cavities with
\nclosed<\/i> flow (see ESDU 00006 \u2013 Reference 96) arising from
\nthe strong upwash at the forward end of the cavity coupled with the
\nequally strong downwash at the rear. The flow is, however,
\ncomparatively steady compared to that in transitional or open
\nflow.<\/p>\n

Of the two, problem area (a) has attracted by far the most
\nresearch effort, not least because it poses the greater challenge
\ndue to the complexity of the unsteady flow involved.<\/p>\n

The adverse cavity flow effects affecting weapons carriage and
\nrelease can be alleviated by various means, both active and
\npassive, see Parts IIIA to IIID (References 99 to 102)*. However,
\nin order for the alleviation mechanism to be effective, a knowledge
\nof the nature of the unsteady flow is essential, and the primary
\npurpose of the present Data Item is to provide wide-ranging
\ninformation on that aspect.<\/p>\n

* Acoustic peaks as high as 180 dB are possible, implying
\npressures around 2 \u00d7 104<\/sup> N\/m2<\/sup> (418
\nlbf\/ft2<\/sup>); even levels of 160 dB can cause damage
\n(Reference 71).<\/p>\n

* This Data Item forms Part II of a series on cavity flows. All
\nthe Parts are listed in Section 2.2 of Part I (Reference 98)<\/p>\n","protected":false},"excerpt":{"rendered":"

Aerodynamics and Aero-Acoustics of Rectangular Planform Cavities – Part II: Unsteady Flow and Aero-Acoustics<\/b><\/p>\n\n\n\n\n
Published By<\/td>\nPublication Date<\/td>\nNumber of Pages<\/td>\n<\/tr>\n
ESDU<\/b><\/a><\/td>\n2009-05-01<\/td>\n127<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n","protected":false},"featured_media":557333,"template":"","meta":{"rank_math_lock_modified_date":false,"ep_exclude_from_search":false},"product_cat":[2675],"product_tag":[],"class_list":{"0":"post-557325","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\/557325","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\/557333"}],"wp:attachment":[{"href":"https:\/\/pdfstandards.shop\/wp-json\/wp\/v2\/media?parent=557325"}],"wp:term":[{"taxonomy":"product_cat","embeddable":true,"href":"https:\/\/pdfstandards.shop\/wp-json\/wp\/v2\/product_cat?post=557325"},{"taxonomy":"product_tag","embeddable":true,"href":"https:\/\/pdfstandards.shop\/wp-json\/wp\/v2\/product_tag?post=557325"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}