Considering the hazards of noise pollutions and their increasing trend, nowadays, sound insulations are of the utmost importance. Some available insulating blankets in the market are made of foam and absorb moisture, while the other types of common insulations are fragile and vulnerable. Most of the insulations cannot be used in available construction materials and decrease the beauty of atmosphere. The insulations, which do not have the mentioned problems, are expensive. The current study aims at introducing an insulation, which does not have these problems and resists moisture at a reasonable price. This insulation is made of natural rubber and polyester fibers. It has a considerable flexibility and can be combined with other construction materials. In this experimental study, different samples of one-layer and two-layer natural rubbers with 2.2 mm thickness for each layer were produced with and without fibers in compression molding method. They were tested in various frequencies and compared with the results of common XPS sound insulation. Each of the samples had a good performance in a specific frequency. All samples exhibited an acceptable behavior compared with their peers in the market. Each of the samples performed better at a certain frequency. In conclusion, the best performance is related to the two-layer rubber sample with fibers and the present insulation in the market is in the second rank.

The sound emission of airplanes has some applications such as localization, classification, and detecting fault. Therefore, investigation of issues, which affects the airplanes sounds, is important. In recent years, pollution of dust in all cities of the Iran shows an increasing trend. In the literature, all variables affecting the sound emission such as temperature, pressure, and relative humidity have been investigated, but there are not any researches about the influence of dust on the atmospheric attenuation coefficient. The experimental tests have been carried out with 3 sensitive microphones, 950m away from the takeoff area of Imam Khomeini international airport for 6 different airplanes, including Airbus 320, 319, 321, Boeing 747, 777, and Embraer 190 at different atmospheric conditions. The air temperature was in the range of 20-40˚C and the relative humidity was in the range of 2-34%. At first, the experimental setup was validated by available data, considering different temperatures and relative humidities. In this research, a new variable, β, has been introduced to detect the dust effect, which is defined as: the difference between the calculated sound pressure level at no dust and the measured sound pressure level while the dust density is 1μgr/m³. Airbus 320 has the minimum dust atmospheric attenuation coefficient value (0.01202db*m³/μgr) and its maximum is related to the Embraer 190 (0.0154db*m³/μgr). Finally, the obtained results show that increasing in dust concentration (PM2.5 and PM10) leads to increase in atmospheric attenuation coefficient between airplane and microphones area, and the measured sound pressure level decreases.

Turbofan engines are widely used in modern aircraft. Low-pressure turbines are the heaviest components of turbofan engines, and reduction of their weights is very effective in improving the specific fuel consumption and overall efficiency of these engines. One of the methods of decreasing the engine weight is to decrease the number of blades which is accompanied by an increase of the blade loading. For this purpose, high-lift airfoils can be used. As the occurrence of flow separation is very probable in high-lift blades, the recognition of the location and size of the separation bubble is important to assess the energy loss of flow. In this research, T106D-EIZ high-lift cascade is simulated by two-dimensional Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations with Shear Stress Transport (SST) turbulence model and γ-Re_θ transition model in two Reynolds numbers 200,000 and 60,000 at a constant isentropic exit Mach number of 0.4, which represent a typical flow condition in low-pressure turbine. The results show that when Reynolds number is high, the separation bubble remains small on the suction side and the separated shear layer returns to the blade surface, and the energy loss of flow decreases. On the other hand, at a low Reynolds number, the separation bubble grows and energy loss increases. Separation bubble is not directly detectable in an evaluation of pressure distribution. However, proper orthogonal decomposition of the pressure field provides the capability to identify flow structures including vortex stretching, the onset of flow separation, and flow reattachment. When the separation bubble is long, large vortical structures are formed on the suction surface. Release of these large vortices can increase the profile loss by more than 50 percent.

Turbocharger turbine blade thickness is restricted by blockage and trailing edge losses and it is exposed to damage due to aerodynamic loads. Proper designing of the blade needs to full recognition of loads on the blade. Therefore, the force from the fluid to the blade should be calculated. Although, thickening the blade results to the more resistance to fracture and cracks, but it affects the aero-structural performance of each section of the blade differently. So, turbocharger turbine blades are exposed to pulsating flow which should be considered in thickness distribution selection. This article reports a comprehensive fluid-solid interaction study of the turbine blades with different thickness distribution which could beneficially investigates the effect of each part thickness on the aerostatic efficiency. Leading edge and trailing edge thickness, maximum thickness and its location, trailing edge shape, hub, and tip blade thickness were the variables which their effects were investigated. Using dual turbocharger turbines leads to lower dissipation of kinetic energy of pulsating charge from the engine. In such turbines, each sector of rotor accepts a different charge from upper and lower entries. The flow distribution of every passage is the difference from the others. Therefore, to the evaluation of the flow, modeling of the entire turbine is needed. 3D CFD model in ANSYS CFX for fluid side and an FEA model in ANSYS Static Structural module for the blade structural responses were used then the results were coupled. Validation was performed by reference to experimental data carried out in imperial college London on a dual turbocharger turbine.
 

In this research, the vibration of a beam treated with a viscoelastic constrained-layer-damping has been studied and the effects of thermal variations and the attached lumped mass on the variation of the optimal design of the constrained layer have been investigated. For modeling the core, the second and third order polynomials were used respectively for out-of-plane and in-plane displacements, and for outer layers, the Euler-Bernoulli beam theory was used. With this modeling, the effect of the through-the-thickness normal strain in the mid-layer (core) can be included in the analyses, and the model will be applicable for studying the cases with moderately thick cores. The finite element method with 3-node elements has also been used for the solution purpose. Moreover, the viscoelastic material is assumed to be isotropic and its constitutive behavior is described by a complex shear modulus dependent on temperature and frequency. This dependence on frequency and temperature has been obtained by using the graphs of the experimental results presented in the relevant references. Numerical studies have been carried out to investigate the variation of the damping and harmonic response amplitude with the thickness of the core and the constraining layer at different temperatures. The results showed that the thermal variation could considerably change the region associated with the optimal design and the maximum damping. This implies that the range of thermal variations in the operating environment of the structure should be considered in designing a viscoelastic-damping layer. In the numerical studies, the effect of added rigid masses on changing the optimal design was investigated. The results show the necessity to consider all the added masses before designing the constrained layer damping.

The intensity of sound in most industries and processes is a disturbing factor. Sound absorbers are a means of reducing noise. There are various types of sound absorbers with different designs and materials, but sound absorbers that can have a high absorption coefficient will be effective. The design of the manger sponge with fractal structure will be a good solution to this problem. Various factors such as composition type, step, and frequency affect this adsorbent. In this research, each of these factors was investigated and analyzed. The effects of the absorption coefficient and changes in sound level influenced by composition type, step and frequency factors were investigated and analyzed. Investigation of the step factor revealed that the amount of absorption coefficient in step 2 had better results compared to the step 1. The absorption coefficient in steps 1 and 2 were 0.3 and 0.38, respectively. Among the effective factors on the amount of absorption coefficient of manger sponge, the composition type was more effective. The results showed that the adsorbent with harder texture has a lower absorption coefficient and the adsorbent with a lighter texture has a higher absorption coefficient. Among the composition type used for this adsorbent, the sponge has a maximum absorption coefficient of 0.4 and MDF has a minimum absorption coefficient of 0.3.

The study of turbulent boundary layer trailing edge noise as one of the most important aerodynamic sound generation mechanisms is a fundamental issue in design and production of equipment with minimum noise. In the present study, the utilization of finlets as a turbulent boundary layer trailing edge noise control technique is investigated. For this purpose, a flat-plate model, equipped with surface pressure transducers has been designed and built and the main parameters of trailing edge noise including the surface pressure spectra, the spanwise length scale, and eddy convection velocity in the trailing edge region have been measured. Moreover, in order to study the structure of the boundary layer flow downstream of the surface treatments, a single hot-wire anemometer has been used. The results showed that the presence of finlets leads to a significant reduction in the surface pressure spectra at all frequency ranges except for frequencies close to the maximum surface pressure spectrum. Furthermore, passing the flow structures through the finlets, although did not create significant changes to the spanwise length scale at high frequencies, however, they have led to an increase at low to mid frequencies. Finally, the Amiet-Roger model has been used to evaluate the changes in far field trailing edge noise due to the presence of the finlets and the results show the effectiveness of finlets in reducing trailing edge noise over a wide range of frequencies.

Thermoacoustic engine is an energy conversion device that uses the energy carrying capacity of sound waves to generate sound power from thermal energy. Although it is not difficult to build thermoacoustic engines due to having no moving parts, many researchers have always tried to reduce the temperature difference required to run thermoacoustic engines, so that these devices can be used in most industries. To investigate the onset conditions of the system, temperature changes in the stack section of a standing wave Thermoacoustic engine were investigated. Numerical analysis of temperature changes along the stack, was performed using the rotts thermoacoustic equations. The temperature was calculated instantaneously along the stack, and this process continued until the thermal equilibrium was established in the system. A standing wave with an open end was designed and built to validate the temperature curves obtained at different moments. This thermoacoustic engine was able to display the temperature instantaneously along the stack with parallel plates structure. The data obtained from the experimental tests and the temperature changes diagram resulting from the numerical solution method, showed a good agreement with each other for the onset process in the system.