Shock associated noise of inverted-profile coannular jets,part I: Experiments

The reduction of shock-associated noise in inverted-velocity-profile coannular jets is quantified and explained by (1) conducting extensive optical and acoustic measurements for a suitable range of outer and inner stream pressure ratio combinations, and (2) interpreting the measured noise results with the aid of new theoretical models. It is shown that the shock noise from the outer stream is virtually eliminated when the inner stream is operated at a Mach number just above unity, regardless of all the other jet operating parameters. Furthermore, this reduction can be achieved at inverted- as well as normal-velocity-profile conditions.     

Shock associated noise of inverted-profile coannular jets,part II: Condition for minimum noise

An experimental and theoretical investigation of shock-associated noise of inverted-profile coannular jets is described. For a fixed fan-stream Mach number, it is observed that the shock-associated noise often drops suddenly to a minimum as the reservoir pressure of the primary jet increases. When this happens, the almost periodic shock cell structure of the fan stream is found to nearly completely disappear. In this paper, an analytical model of this phenomenon is constructed and studied. It is theoretically established that this sudden change in the shock structure and hence the decrease in shock associated noise would occur when the primary jet flow is just slightly supersonic regardless of the Mach number and temperature of the fan stream. This minimum shock associated noise condition is confirmed in several series of experiments.     

Shock associated noise of supersonic jets from convergent-divergent nozzles

Results of experimental and theoretical studies of the characteristics of shock associated noise from imperfectly expanded supersonic jets over an extensive range of underexpanded and overexpanded operating conditions are described. This kind of broadband noise is believed to be generated by the weak but coherent interaction between the downstream propagating large scale turbulent flow structures in the mixing layer of the jet and the nearly periodic shock cell system. Theoretical reasoning based on this mechanism leads to the scaling formula that the intensity of shock associated noise varies as (M_j² ? M_d²)² where M_j and M_d are the fully expanded jet operating Mach number and nozzle design Mach number, respectively. This formula holds for underexpanded as well as overexpanded jet Mach numbers. In addition, a peak frequency formula is also derived from the same model. The noise intensity, directivity and spectra of supersonic jets from a convergent-divergent nozzle of design Mach number 1·67 were measured in an anechoic facility over the Mach number range of 1·1 to 2·0. The effect of jet temperature was investigated by operating the jet at three temperature conditions. These sets of data provide sufficient information for fully assessing the relative importance and characteristics of shock associated noise of supersonic jets from convergent-divergent nozzles. Comparisons between theoretical results and measurements show very favorable agreement.     

An experimental study of jet noise part II: Shock associated noise

The characteristics of the sound field of shock-containing under-expanded jet flows are studied by measuring the noise from a convergent nozzle operated over an extensive envelope of supercritical jet operating conditions. The measurements were conducted in an anechoic facility. They are complementary to the turbulent mixing noise experiments (described in Part I) for subsonic and fully-expanded (shock-free) supersonic jets. The overall results from shock-containing jets are compared directly with the corresponding results from shock-free jets, and the effects of nozzle pressure ratio and jet exhaust temperature on broadband shock-associated noise are assessed independently. For a supersonic jet, the regimes of jet operating conditions, observer angles, and frequencies over which the sound field is dominated by shock-associated noise are identified. Finally, the spectral results are compared in a preliminary manner with the spectra predicted by an existing theoretical model, and good agreement is obtained in most cases.     

The effects of site selected variables on human responses to traffic noise,part III: Community size by socio-economic status by traffic noise level

This paper reports the results of the third part of a field study of human responses to traffic noise. The influence of traffic noise level, community size, and socio-economic status were investigated in a controlled manner determined by subject selection procedures. Human responses were obtained from interviewer administered questionnaires, and were as spatially and temporally coincident with the noise measurements as possible. Noise measurements were obtained from several days of rapidly sampled digital recordings. Traffic noise level was the major predictor of the intensity of elicited responses. A number of other significant effects were observed largely related to community size. These were explained as due to parallel variations in the perceived necessity of vehicles, the annoyance with aircraft noise, and the logarithm of the vehicle flow rate. The results did demonstrate effects related to community size, and thus it is unwise to extrapolate the results of large city noise studies to small communities and rural areas.     

Weber electrodynamics: part III. mechanics,gravitation

Weber electrodynamics predicts the Kaufmann-Bucherer experiments and the fine structure energy level splitting of the H-atom (neglecting spin) without mass change with velocity (i.e., mass ). The Weber potential for the gravitational case yields Newtonian mechanics, confirming Mach's principle. It provides a cosmological condition yielding an estimated radius of the universe of 8 × 10⁹ light years. Despite these successes, the independent evidence for Kaufmann mechanics, where mass changes with velocity (i.e., mass ) is convincing. Perhaps a slight alteration may make the Weber theory compatible with Kaufmann mechanics.     

Propeller aircraft interior noise model,part I: Analytical model

Theoretical results are given for a basic propeller aircraft interior noise model. Results allow prediction of tonal levels in the cabin of a propeller-driven airplane at the blade passage frequency and its harmonics. Part I of this paper contains the analytical model, and in Part II scale-model and flight test comparisons are considered.     

An experimental study of jet noise part I: Turbulent mixing noise

The characteristics, both spectral and directivity, of turbulent mixing noise in the far field from subsonic and fully-expanded supersonic jet flows have been studied experimentally over an extensive envelope of jet operating conditions (jet exit velocity and temperature). The measurements were conducted in an anechoic room which provides a free-field environment. The results are presented in a systematic manner, and the observed trends and dependencies are discussed in detail. In particular, the changes in detailed jet noise features with varying velocity and exhaust temperature are assessed independently. Empirical prediction schemes or comparisons with recent theoretical investigations are not attempted here. However, the isothermal jet noise results are compared with those predicted by the freely-convecting quadrupole theories (that is, in the absence of any mean flow shrouding effects). The discrepancies between this model and the measurements, many of which have been recently shown to occur due to the presence of mean velocity and temperature gradients surrounding the sources, are obtained accurately over all jet operating conditions of interest.     

Propeller aircraft interior noise model,part II: Scale-model and flight-test comparisons

Part I [1] of this paper contains the theory used to create a basic propeller aircraft interior noise model. The model predicts tonal levels of blade passage harmonics in the cabin of a propeller driven aircraft. Part II presents the results of validation studies based on scale-model and flight comparisons.     

The NLO jet vertex for Mueller-Navelet and forward jets: The quark part

We calculate the next-to-leading corrections to the jet vertex which is relevant for the Mueller-Navelet-jets production in collisions and for the forward jet cross section in ep collisions. In this first part we present the results of the vertex for an incoming quark. Particular emphasis is given to the separation of the collinear divergent part and the central region of the produced gluon. Received: 16 January 2002 / Published online: 5 April 2002     

The NLO jet vertex for Mueller-Navelet and forward jets: the gluon part

In this paper we complete our calculation of the NLO jet vertex which is part of the cross section formulae for the production of Mueller Navelet jets at hadron hadron colliders and of forward jets in deep inelastic electron proton scattering. Received: 2 September 2002 / Revised version: 16 January 2003 / Published online: 2 June 2003 RID="a" ID="a" Supported by the TMR Network "QCD and Deep Structure of Elementary Particles" RID="b" ID="b" Supported by the Alexander von Humboldt Stiftung     

Amplitude and frequency characteristics of acoustic jets

The prerequisites to formation and the characteristics of a jet that occurs at the open end of a waveguide guiding an intense sound wave are studied. The velocity field is measured by a hot-wire anemometer. The previously developed method of separating the jet velocity V_jet from the amplitude of the oscillating particle velocity V_osc, which is applicable only when V_jet>V_osc, is supplemented with the method of oscillogram processing applicable for V_jet≤V_osc. Thus, a full picture of the jet evolution in space, starting from the waveguide outlet, is obtained. The experimentally determined spatial distribution of the jet velocity is found to agree well with the numerically simulated dependences reported by other authors. For the oscillating velocity amplitude at the open end of the waveguide, a threshold value, beyond which the formation of the acoustic jet takes place, is revealed. The frequency dependence of this threshold value is determined. The dependence of the maximal jet velocity on the oscillating velocity amplitude in the outlet waveguide cross section is found to be close to linear.     

主变压器噪声特性分析及复合隔声结构设计*

超高压变电站的主变压器的噪声影响已引起广泛关注。以某典型化设计的500kV变电站A的主变压器为例,进行了现场测试,得到其主变压器噪声能量主要集中在中低频范围内,且具备明显的线谱噪声特征。针对该噪声特点,提出了一种内插微穿孔板的双层带孔板型声学超材料的复合隔声结构。使用传递矩阵理论对该复合结构进行了分析,并在阻抗管中进行了实验验证。实验结果表明：该复合隔声结构具备针对性隔声要求,理论与实验传递损失曲线基本吻合。