Abstract: In order to investigate the characteristic of the supersonic jet screech tones, an experimental bench of the supersonic jet was designed and a free field noise signal acquisition system was established. Effects of the nozzle size and jet Mach number on jet noise sound field distribution was analyzed, through the result comparison of supersonic jet noise experimental measurement. Results indicate that the field distribution of supersonic jet screech tones is characterized with very strong directivity. Peak value of the screech tones decrease and occurrence frequency of the screech tones increase with the decreasing jet exit Mach number; occurrence frequency of the screech tones decrease with the increasing nozzle size, but the peak value change very less. The experimental measurement of supersonic jet noise provides mechanism research of sound production with data supports and references; and also provides the numerical modeling of supersonic jet noise with validation criteria.
Abstract: In this paper a 3-D numerical model is used to investigate the thermal performance of a three aligned unit of NDDCT under crosswind condition. The computed results show that, there are major differences in computed velocity patterns and pressure fields around the cooling tower due to neighboring of a number of cooling towers will result considerable changes in computed flow parameters hence; the thermal performance losses for the single tower under crosswind are superior to those when this towers are incorporated in aligned arrangement. Results also show that the best thermal performance of the three aligned NDDCT is achieved when the crosswind is directed along the towers connection line.
Abstract: Compressor is a dynamic machine with complicated 3d aerodynamics. Dynamics creates an uncertain environment and induces the flow with instabilities, resulting in reduced performance. Motion being circumferential, flow is also subjected to rotational accelerations. Added to these complications are the tip gap and related vortex aerodynamics in the tip region, which also influence the passage flow of the rotor and thus complicates the flow field. The result of these implications is the generation of the turbulence in the flow field. Turbulence is a fluctuating characteristic of the flow, which extracts its energy from the mean flow field. Energy consumed by the turbulent nature of flow is a waste. Therefore it is very much important to understand about the influence of the turbulence and related kinetic energy compressor aerodynamics. In this paper work is presented to understand about the turbulence under such varying geometry conditions of flow, as well as blade. Results of nature of the turbulence and its growth are discussed for varying mass flow rates and different tip gaps of acceptable range.
Abstract: Wind tunnels are the experimental apparatuses which provide an airstream flowing under controlled conditions so that interesting items in aerospace engineering such as pressure and velocity can be tested. In this work, Shock wave passes through the intermittent blow-down wind tunnel at Mach=2,3,4 has been investigated. The shape of the nozzle contour for a given Mach number was determined using the method of characteristics. For this purpose MATLAB code was developed and this code was verified with Osher’s and AUSM methods, FORTRAN code and FLUENT software was used for these two methods, respectively. Dimensions of different parts of wind tunnel are determined and minimum pressure ratio for the starting condition has been founded using FLUENT software. Good agreement was considered compared with the data from eleven tunnels over their range of Mach number.
Abstract: Viscous drag on the internal surfaces of a notional scramjet engine model has been estimated through Reynolds analogy, using measured wall heat transfer rates, in a shock tunnel at a hypersonic Mach number of 8. The study has been carried out without fuel injection and at zero degree angle of incidence of the model with the freestream. The heat transfer rate measurements were carried out on the upper and lower internal surfaces of the engine employing fast response E-type thermocouples. Application of Reynolds analogy to the wall heat transfer rates yielded the skin friction coefficient, through which the viscous drag on the surfaces could be determined. The measurements predict the salient features of the flow field of the model and are a novel reference on the data to the researchers working in the area of slender-body, hypersonic aerothermodynamics.
Abstract: Hypersonic flow of Mach number 8 past a 25°-50° double cone geometry is numerically simulated at ReD=4.8E5. Complicated flow structures, including Type V shock-shock interaction, shock-boundary layer interaction, separation and reattachment at the corner are presented and discussed. The surface pressure and heat transfer rate distributions are also calculated and compared with the experimental data. Results show that both the 2nd order MUSCL and 5th order WENO could accurately reproduce the shock structures, while the higher order scheme could predict a more accurate size of separation zone. Generally, the size of the separation zone is underestimated with an overvalued pressure distribution after reattachment employing the full turbulent models. On the other hand, transition induced by the reattachment shock has been calculated using transition model and the results of pressure peak and the size of separation zone show good agreement with the experimental measurements.
Abstract: The geometrical optimization of dump diffusers are extremely demanding as the flow fields and stress fields are very complex and must be well understood to achieve the required design efficiencies. In this paper parametric analytical studies have been carried out for examining the aerodynamics characteristics of different dump diffusers for modern aircraft engines. Numerical studies have been carried out using SST K- ω turbulence model. This code solves SST k- ω turbulence equations using the coupled second order implicit unsteady formulation. In the numerical study, a fully implicit finite volume scheme of the compressible, Reynolds-Averaged, Navier-Stokes equations is employed. We concluded that in addition to the dump gap ratio, the aerodynamic shape of the flame tube case and the other geometric variables are also need to be optimized judiciously after considering the fluid dynamic constraints for controlling the pressure recovery and the losses.
Abstract: Aiming at the wind load evaluation in the mechanical structure design of solar photovoltaic power generation station with sun tracking, a numerical wind tunnel model was established based on the computational fluid dynamics theory and finite element method. The 8-level wind velocity was applied in the model considering the mal-condition of reef islands and Gobi desert where the solar photovoltaic power generation station usually installed. From the numerical simulation results, the influence of elevation angle of the solar cells on the wind load was presented. To decrease the maximum wind load on the power station, the gap between solar cells was proposed as air vent in this paper, which has been adopted in a prototype machine, and more than 20% of the equipment weight has been reduced.
Abstract: Ejectors are devices usually made of two convergent/divergent coaxial nozzles which are used to convert pressure energy into kinetic energy. These devices involve very complex phenomena which strongly affect their performance. Flow visualization methods are often used to provide precious information as for the nature of the flow within the ejectors and the comprehension of the physical phenomena encountered. Unfortunately, the visualization methods used successfully until now in these systems are primarily qualitative techniques. Some attempts at quantitative flow visualization by Particle Image Velocimetry have been carried out in quite specific applications but with mitigated results due to the complicated conditions of investigation. The objective of this paper is to present an attempt at PIV measurements in a supersonic air ejector. Several ejector operating conditions and flow seeding methods are taken into consideration. The velocity fields obtained are compared with CFD simulations of the flow and allow the rigorous validation of numerical models.
Abstract: At present, only the flat ground surface problem is investigated in most studies on ground effect, which is not effective for practical applications due to the universal existence of curved ground surface. In this paper, the lift calculation of a two-dimensional flat plate airfoil placed near a curved ground surface is investigated. In order to calculate the complex velocity in the flow field, the complex variable function theory is employed. The conformal mapping method is applied to transform the flat plate airfoil to a cylinder in the uniform flow. Moreover, the discrete vortices method is modified to convert the curved ground surface to a series of discrete boundary elements. Two kinds of curved ground surfaces are considered: semicylindrical hollows and semicylindrical hills. It is shown that the lift fluctuation of flat plate airfoil located near a hollow or a hill is considerably serious, which should be considered during the design of flight vehicles flying near the ground surface.