A Study On Fluid Excitation Effect On Tightly Packed Tube Bundle

With the application of the large scale of production,the increase in flow rate and the high strength material,the large scale,high efficiency and low cost requirements of heat exchanger are proposed,where the problem about fluid induced vibration is becoming more and more prominent.The fluid induced vibration force can cause the vibration of the tube bundle,which may cause fretting wear or fatigue damage to the equipment used for a long time.The vortex shedding force and turbulence are the initial conditions for the instability of the tube bundle,and the study of the fluid excitation effect is also important for the fluid solid coupling.At present,the study on the effect of fluid induced vibration on a packed tube bundle has been widely concerned by scholars in this field.First of all,this paper takes the method of water tunnel experiment to study the fluid force of the rigid tube bundle with a pitch ratio of 1.28.The experimental tube bundle includes four kinds of common arrangement: the regular triangle arrangement,the corner square arrangement,the triangle arrangement and the square arrangement.With the fluid force measured on a packed tube bundle,we analysis the influence of time domain and frequency domain characteristics,the composition structural characteristics of fluid force and flow calculation and analysis of the physical convection,providing experimental data for the bounded noise analysis model and numerical calculation.On a packed tube bundle,the fluid forces are out of order in the time domain,while they can reflect more characteristics of the amplitude and components in the frequency domain,especially the relative amplitude of periodic component and random component.The fluid turbulence is stronger in the square tube,which has no quasi periodic characteristics;the periodic characteristics are stronger square in the rotated square bundle,which are much more obvious in the first few rows of periodic quasi periodic degree;those are between the former for the normal triangle and rotated normal triangle in the bundle.For the same pipe,in the range of Reynolds number,the turbulence excitation force coefficient is not sensitive to the variation of the flow condition.Secondly,based on the large eddy model of commercial software ANSYS Fluent,the flow field and periodic vortex shedding in four configurations and three kinds of pitch ratios(1.28,1.50 and 2.00)are calculated and analyzed.At the same time,the calculated results are compared with the corresponding experimental data,and the feasibility of the numerical method is verified.From the analysis of the flow field contours with different arrangement,the influence of composition on flow field between the tube bundle arrangement is mainly off the formation of wake interference to the adjacent downstream periodic vortex tube locates the position and angle.And this phenomenon is particularly evident in the corner of a normal square arrangement and a rotated normal square arrangement of tube bundle.With the increase of the tube spacing,the vortex shedding disturbance weakened.Correspondingly,with pitch diameter ratio increases,Strouhal number has a certain degree of decrease or from scratch.With the study on Strouhal number,a similar conclusion has been reached with the above conclusion.On a packed tube bundle,the periodic component of the fluid force is not sensitive to the Reynolds number.Finally,based on the experimental data of the tube pitch to diameter ratio of 1.28 tubes,the applicability of the bounded noise model in the low frequency region of the power spectrum density of the fluid exciting force is studied.For the bounded noise model of the fluid exciting force,it is necessary to carry on the preliminary optimization processing: the dimensionless transformation of the power spectral density and the noise reduction of the power spectral density;In the parametric analysis of bounded noise model,the parameters of bounded noise model include peak frequency,signal amplitude and noise intensity.In the study of the fluid forces on a packed tube bundle,they correspond to the number of the equivalent values of the hydrodynamic force and the equivalent energy.Through the analysis of the applicability of the bounded noise model,it is found that the bounded noise model is more suitable than the normal one because of the quasi periodic characteristics of the flow in the staggered tube bundle.