{"title":"A simple model of shock cell noise generation and its reduction","authors":"Y. Chan","doi":"10.1121/1.1913631","DOIUrl":"https://doi.org/10.1121/1.1913631","url":null,"abstract":"Based on the data of near field surveys of the sound pressure from a choked jet, a simple model is proposed for the mechanism of the screech generation. A convected wave propagates downstream along the jet boundary and is modulated by its interaction with the shock-expansion waves of the jet. These interactions generate strongdipoleradiations. Using this model, an excellent reproduction of the essential features of the experimental results is obtained. By preventing the formation of shock waves inside the jet, the strong dipole radiation and hence the screech noise can be eliminated. Design data for perforated nozzles to achieve fuU expansion of the jet are provided. This avoids the mechanical complication of an adjustable convergent-divergent nozzle.","PeriodicalId":165529,"journal":{"name":"National Research Council, Aeronautical Report LR","volume":"23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1972-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134387760","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"An investigation of the near noise fields of a choked axisymmetric air jet","authors":"R. Westley, J. Woolley","doi":"10.3138/9781487582869-009","DOIUrl":"https://doi.org/10.3138/9781487582869-009","url":null,"abstract":"An experimental investigation was completed of the near sound field of a choked axisymmetric air\u0000jet of 2.25-in diameter. The results include surveys of tbe sound pres sure levels in the area surrounding the jet and the identification of various screech frequencies.\u0000A schlieren system with stroboscopic spark synchronisation was used to photograph an axisymmetric\u0000mode and a spiralling mode of the jet oscillations.","PeriodicalId":165529,"journal":{"name":"National Research Council, Aeronautical Report LR","volume":"35 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1968-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124993093","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Stability derivatives of sharp cones in viscous hypersonic flow","authors":"R. Kind, K. Orlik-Rückemann","doi":"10.2514/3.3712","DOIUrl":"https://doi.org/10.2514/3.3712","url":null,"abstract":"Using approximate forms of the existing pressure relations for an inclined flat plate, a theory has been developed for the determinat ion of static and dynamic stability derivatives of steady and oscillating sharp wedges in viscous laminar hype rsonic flow. The pressure field over the wedge has been assumed to consist of directly intersecting and suitably matched regions of weak and strong viscous pressure interactions. The concepts of static and dynamic viscous pressure interactions have been introduced, which are related to the effective change of the deflection angle and the normal velocity, respectively, of the wedge surface due to the presence of boundary layer. Closed expressions have been derived for the stability derivatives using a generalized form of the piston theory in which the regions of simple-shock or weak-shock approximations were graphically matched to the region of st rong-shock approximation. Static derivatives, which are affected only by the static viscous interaction, are given partly in the fonn of viscous derivatives, obtained by use of the piston theory, and partly in the form of viscous correction factors, which can be applied to inviscid derivatives obtained by arbitrary means. Viscous effects are shown to act in a stabilizing manner for moments taken about axes forward of the one-third chord position and a destabilizing manner for more rearward axis positions. Dynamic de rivatives are affected by both the static and dynamic viscous interactions. The effect of the static interaction on the damping-in-pitch derivative is shown to be always positive.","PeriodicalId":165529,"journal":{"name":"National Research Council, Aeronautical Report LR","volume":"28 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1965-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116798264","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Flow of heat from a wedge into a surrounding medium","authors":"P. Mandl","doi":"10.3138/9781487584443-016","DOIUrl":"https://doi.org/10.3138/9781487584443-016","url":null,"abstract":"In this report the transient temperature field due to the cooling of a thin, liquid wedge by a surrounding infinite solid is calculated. It is shown that there exists a self-similar solution which is a function of two indepedent variables, namely, the angular co-ordinate and a combination of radial distance, time and diffusivity. \u0000On the assumption that the change in phase of the medium may be ignored, a solution in infinite series for the temperature field is derived, using a step-by-step procedure. When the theory is applied to a practical case, the step-by-step calculations converge rapidly everywhere, except near the tip of the wedge. The predicted motion of the isothermal surfaces is displayed graphically for an arbitrary time sequence. From these results it may be inferred that solidificatlon proceeds from the vertex primarily in the radial direction.\u0000An attempt is made in the appendix to extend the theory by allowing for a change in the state of the medium. Certain applications of the theory to other heat conduction problems are suggested.","PeriodicalId":165529,"journal":{"name":"National Research Council, Aeronautical Report LR","volume":"87 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1961-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122085857","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}