船舶螺旋桨叶片与艉部湍流场互作用噪声的预报研究

低噪声特性是螺旋桨设计者所追求的目标之一。当船尾的螺旋桨周期性旋转在空间和瞬时随机的非均匀流场中时,在螺旋桨叶片上就会产生升力脉动,从而辐射出离散谱噪声和低频宽带噪声。利用湍流谱和FfowcsWilliams-Hawkings方程可以获得低频宽带噪声级。这种方法可用于实船螺旋桨噪声预报和低噪声设计,这对提高舰船安静化程度有重要的现实意义。     

Effects of finite inner and outer scales on the scintillation index of turbulent slant path

In this paper, the effects of nonzero inner scales and finite outer scales are investigated, in the context of Gaussian beam propagation along a slant path under general turbulence conditions. Theoretical expressions for the cut-off spatial frequencies are derived with an approach method, and thereby a modified scintillation model is developed to incorporate inner scale and outer scale parameters in the analysis. Then, inner and outer scale effects on the downlink are analysed with respect to the zenith angle, the altitude of the transmitter, the initial beam radius, as well as the turbulence strength. Numerical results indicate that the effects of a finite outer scale mainly influence transmission that occurs at large zenith angles or high altitudes, while the inner scale effects are more prevalent. This study may be helpful to improve the accuracy of calculation of slant-path scintillation index, and thus benefit the characterization and optimization of space/air-ground laser communication systems.     

Effect of rotor cage's outer and inner radii on the inner flow field of the turbo air classifier

The effects of rotor cage's outer and inner radii on flow field of the turbo air classifier are comparatively analyzed by numerical simulation using ANSYS-FLUENT. The results of quantitative analysis show when the rotor cage's outer and inner radii are increased, the tangential velocity, radial velocity and upward axial velocity decrease in the annular region and near the entrance of the rotor cage. However, when the rotor cage's outer and inner radii are too large or too small, the tangential velocity and radial velocity will be fluctuated greatly. Moreover, the rotor cage's outer and inner radii directly influence the radial velocity distribution in the rotor cage channel. The rotor cage's outer and inner radii should not be too large or too small. Therefore, in the seven contrast rotor cage models, model 100–70 and 90–60 are selected to carry out the calcium carbonate classification experiments due to their small tangential velocity and radial velocity fluctuations and well-distribution in the rotor cage channel. The experimental results reflect the characteristics of the numerically simulated flow field in the classifier.     

Calculation of electric arc interaction with a turbulent gas flow

The characteristics of an electric arc in a turbulent gas flow are studied. Relationships for calculating turbulent transport are presented.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 54, No. 4, pp. 550–557, April, 1988.     

Analysis of interaction of single-layer monolithic damping coatings with turbulent flow

The article analyzes the effect of the spectral-energy and phase-frequency oscillation characteristics of damping coatings on the friction coefficient and on turbulent pressure pulsations.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 51, No. 6, pp. 959–965, December, 1986.     

Fully developed turbulent flow with macrovortices in an annular channel with rotating inner cylinder

The author has made an experimental study of the process of heat and mass transfer associated with the evaporation of a liquid from an open surface in a rarefied gas medium. The total gas pressure was varied from 1·10⁵ to 1.33·10³ N/m².     

The effect of Brownian motion on collisions between aerosol particles in turbulent flow

A statistical model is given for determining the kernel of collisions of small aerosol particles in homogeneous isotropic turbulence in view of Brownian motion. The suggested model is based on the kinetic equation for the probability density function of distribution of relative velocity of two particles. Analysis is performed of the effect of Brownian motion on the relative velocity of two particles (transport effect) and on the radial distribution function (accumulation effect).     

The spatiotemporal field of turbulent flow pulsation

Relations describing the spatiotemporal field of pulsation of the hydrodynamic parameters of a turbulent flow have been derived based on the wave model of turbulence. The process of chaotization of the pulsation field is analyzed. The results of calculations of the longitudinal and transverse velocity pulsation components are compared to the results of measurements reported by H. Reichardt.     

Edge states intermediate between laminar and turbulent dynamics in pipe flow

We studied the dynamics near the boundary between laminar and turbulent dynamics in pipe flow. This boundary contains invariant dynamical states that are attracting when the dynamics is confined to the boundary. These states can be found by controlling a single quantity, in our case the energy content. The edge state is dominated by two downstream vortices and shows intrinsic chaotic dynamics. With increasing Reynolds number the separation between the edge state and turbulence increases. We can track it down to Re=1900, where the turbulent lifetimes are short enough that spontaneous decay can also be seen in experiments.     

Cascade and through-flow theories as inner and outer expansions

Through-flow theory and cascade flow theory are well known techniques used as efficient tools in order to build approximations to the actual flow in an axial turbomachine. Here we use a technique of matched asymptotic expansions in order to glue together these two kinds of approximations. Throughflow theory forms the basis for the outer expansion while cancade theory forms the basis for the inner one: matching provides boundary conditions for both flows. It appears that for the downstream throughflow, a technique of multiple scales is necessary, in the vibrating case, in order to deal with the unsteady wakes, generated by the vibrating blades, and slowly modulated, downstream by the steady part of the throughflow.     

The coagulation of aerosol particles in turbulent flow

A statistical model is given for determining the kernel of coagulation in the presence of turbulent, Brownian, gradient, and gravitational mechanisms of collisions in view of accumulation effect.     

The metastability of low-pressure water in turbulent flow

Results are given of an experimental investigation of superheating of water at low pressures of 32–170 kPa, which rises up the thrust adiabatic region (d = 0.05 m, H ≈ 20 m) of circulation loop at a velocity of 0.05–0.42 m/s (Re = ((9?72) × 10³). The values of maximal superheating of water relative to the saturation temperature in the cross section being treated are determined, as well as their dependences on the parameters of water flow. Based on the experimental results, closing relations are suggested.     

The interaction between gas-dynamically accelerated particles and a body subjected to flow

Based on the published experimental data, heuristic expressions are suggested for the recovery factors of velocity of particles colliding with the surface of a solid body, which are suitable in the region of rebound (from adhesion to erosion). Numerical investigations are performed of a supersonic gas flow past a sphere, this flow issuing from a nozzle with a wide angle of the diffuser part which provides for a wide range of angles of collision of the particles being accelerated with the body.     

Effect of particle-wall interaction on triboelectric separation of fine particles in a turbulent flow

Triboelectric separation is an effective way to separate fine powders with particle sizes and densities in the same order of magnitude. Many relevant process variables influence the charging behaviour; however, the corresponding effects on the subsequent separation of particles remain unknown. To utilize triboelectric separation as a powerful tool for fine powder separation, process parameters such as the choice of contact wall materials in the charging region have to be investigated. We report for the first time the influence of the tube’s wall material, in which particle charging took place, on triboelectric separation of fine protein-starch mixtures. Different electrically insulating materials along the triboelectric series were tested. No significant influence of the wall material on the separation selectivity and efficiency was found. In addition, particle-wall interaction was inhibited using an experimental setup which allows to control the flow boundary-layer by blowing out air through the tube wall. Also the results obtained by this novel setup showed no significant differences compared to the setup with particle-wall interactions. Additionally, CFD simulations were used to confirm the absence of particle-wall interactions in the boundary-layer control setup. A variation of the boundary-layer thickness leads to a constriction of the particle-containing flow region in the centre of the pipe. Experiments show that this compression of the particle flow zone results in no further increase in selectivity and efficiency of separation. Thus, particle-particle interaction is the prevalent triboelectric charging mechanism of fine powders charged in a turbulent flow regime.     

The 1999 James Lighthill Memorial Paper: Scaling laws for turbulent wall-bounded shear flows at very large Reynolds numbers

Deep ideas of Sir James Lighthill concerning turbulent flows are discussed in the beginning. The scaling laws for large-Reynolds-number flows are presented in their historical development. The underlying hypotheses are discussed and compared with experiments. Special attention is given to non-universal Reynolds-number-dependent scaling laws that reveal the incomplete similarity of the flows. Recent results concerning scaling laws for boundary layers are presented in more detail and discussed.     

Excitation of 3D-disturbances in wall-bounded shear flow with adverse pressure gradient

Summary The excitation of 3D disturbances by a time-harmonic Dirac point source at the wall in a decclerated and a flat-plate boundary layer is compared. It is demonstrated that the linearized parallelflow theory including the receptivity problem can capture the main features of unstable 3D wavetrains found in previous experiments. Depending on the exciting frequency, three different types of wavetrains are identified.     

A numerical study of partitioned fluid-structure interaction applied to a cantilever in incompressible turbulent flow

This study presents an approach for partitioned fluid-structure interaction (FSI) applied to large structural deformations, where an incompressible turbulent solver is combined with a structural solver. The implementation is based upon two different open-source libraries by using MPI as a parallel communication protocol, the packages and OpenFOAM. FSI is achieved through a strongly-coupled scheme. The solver has been validated against cases with a submerged cantilever in a channel flow to which experiments, numerical calculations and theoretical solutions are available. The verification of the procedure is performed by using a solid-solid interaction (SSI) study. The solver has proven to be robust and has the same parallel efficiency as the fluid and the solid solver stand-alone.