Обґрунтування моделі турбулентної в’язкості для дослідження характеристик співвісного гвинтовентилятора і вхідного пристрою ГТД

The issues of substantiation of the most rational, based on adequacy, model of turbulent viscosity for mathematical modeling of the flow near the propfan and in the inlet of the turbine-propeller engine are considered. It was found that at present there is no universal turbulence model for determining the parameters of the boundary layer, energy loss in the flow, and laminar-turbulent transition. Analysis of the results of previous studies showed that there is a need to select and justify a turbulent viscosity model for each type of research object. The task of modeling the flow near the propfan and in the inlet device of the power plant was performed using the ANSYS CFX software product, which allows using various standard mathematical models and tools for modeling turbulent flow. The object of research is an annular axial inlet device, in front of which there is a coaxial propfan with two rows of propellers: the first row has eight blades, the second - six. 7 types of models of turbulent viscosity, which most fully describe the phenomena in the flow around the propfan and the inlet device, have been investigated: k-ωmodel; SSТ (shear stress transport) SST Transitional №1 Fully turbulence; SST Transitional №2 Specified Intermittency; SST Transitional №3 Gamma model; SST Transitional №4 Gamma theta model; SST Transitional №5 Intermittency. The results of mathematical modeling of the flow near the propfan and in the inlet device at the corresponding operating mode of the turbopropfan engine using the selected models of turbulent viscosity, the total pressure value in front of and behind the inlet device was obtained to determine the total pressure recovery coefficient in it and the value of the propfan thrust. The value of the recovery factor of the total pressure in the inlet device and the propfan thrust are compared with the flight test data of the prototype. An analysis of the comparison of the values of the total pressure recovery factor in the inlet device and the propfan thrust showed that the use of the SST Transitional №4 Gamma theta model allows obtaining the value of the total pressure recovery factor in the inlet device and the propfan thrust that is closest to the flight test results.

Удосконалення характеристик кільцевого вхідного пристрою авіаційної силової установки з гвинтовентилятором

The article considers the method of improving the characteristics of the ring inlet device, taking into account the influence of the propeller of an aircraft power plant with a turboprop engine. It is shown that increasing the total pressure loss in the inlet device by 5% increases, approximately, the specific fuel consumption by 3% and reduces engine thrust by 6%, and uneven flow at the inlet to the engine is the cause of unstable compressor of the turboprop engine. It is proposed to improve the characteristics of the input device by modifying the shape of its shell and channel. Evaluation of the influence of the shape of the shell and the channel of the annular axial VP on its main aerodynamic characteristics, taking into account the non-uniformity of the flow on the fan in the calculated mode of operation of the SU is carried out by calculating the full pressure recovery factor. The object of the study is an annular axial input device in front of which is a coaxial fan turboprop fan. The process of modeling the influence of the shape of the shell and the channel on the recovery factor of total pressure, circular and radial non-uniformity of the flow through the input device is implemented in the software system of finite element analysis ANSYS CFX. Geometric models of coaxial screw fan, fairing and inlet device are built in ANSYS SpaceClaim and transferred using the built-in import function in ANSYS Workbench. Block-structured grid models of air propellers of the first and second rows of the fan in the amount of 1.9 million, fairing and inlet device, in the amount of 3.9 million, are built in the ANSYS TurboGrid environment. The standard Stern (Shear Stress Transport) Gamma Theta Transition was used to close the Navier-Stokes equation system. Based on the results of mathematical modeling of flow in coaxial fans and subsonic ring inlet device on the maximum cruising mode of the turboprop engine, the full pressure recovery factor is calculated and it is established that the most influential factor that increases its full pressure recovery factor.

DEGREE OF REGENERATION OPTIMIZATION FOR CYCLES OF MICROGAS TURBINE PLANTS

A consideration subject in article is the mathematical model of pressure recovery factor of microgas turbine plants (MGTP) regenerators which considers dependence of hydraulic resistance of the heat–exchanger on the its surface area. Optimization of a regenerative cycle of MGTP and a cycle with regeneration and the turbocompressor utilizer for the purpose of further increase in their profitability is performed. It is established that use of the offered model of pressure recovery factor on the air and gas side allows to find degree of regeneration heattechnical optimum. This model can be used at simplified and predesign of MGTP.

Enhancing Fractional Flow Reserve Procedure in Stenosis Diagnosis

Stenosis is abnormal narrowing of blood vessels that causes a shortage in blood supply and a blockage of an artery Diagnosis of its severity guides the physician to determine the most appropriate treatment plan. Fractional flow reserve (FFR) is currently the most accurate procedure in stenosis diagnosis. It is a guidewire based technique that uses a small sensor on the tip of the wire to measure proximal and distal pressure of the stenosis. The difficulty of using such method is placing the guidewire precisely in centerline of blood vessel. Therefore, the main objective of the current study is to investigate how the measured pressure varies with the guidewire position. Accordingly, three different positions from the blood vessel centerline along with three degrees of severity are considered. The governing equations for blood flow are obtained and numerically simulated. Numerical results are validated using the available experimental and numerical data. A good agreement between predicted and measured values are obtained. Based on the predicted results, pressure drop coefficient (CDP) and pressure recovery factor (η) are computed. The predicted results with and without the effect of existing guidewire at different location are analyzed and the certainty of fractional flow reserve is reported and discussed. The current method is very helpful to increase the accuracy of fractional flow reserve procedure in stenosis severity estimation.

Steam Turbine Axial Exhaust Diffuser Investigation Using a Test Rig and its Numerical Model

Exhaust casings are one of the most important steam turbine components. The main purpose of the exhaust casing is to increase the last stage enthalpy drop, which results in an increase of the whole turbine output. It plays a significant role especially in turbines with lower outputs and in turbines whose condenser is cooled by air. In such cases, the exhaust casings with an axial diffuser is usually used. This paper deals with the investigation of the axial diffuser outlet part based on experimental measurements performed on a test rig installed in a wind tunnel in the Doosan Skoda Power laboratories and numerical simulations. The first part of the paper is about the general issues appearing the exhaust diffusers. Then, the design of the experimental test rig which aim is to simulate the flow conditions in real turbines is described. The last part of the paper is about experimental measurement as well as numerical results. The main observed phenomenon which is the effect of the circumferential angle on the inlet of the diffuser is described on different designs which were tested from the static pressure recovery factor point of view. For measuring flow parameters, a static wall pressure measurement was used together with multi-hole pneumatic probes. For numerical simulations, the commercial code ANSYS CFX 18.2 was used.

Numerical Investigation of the Circumferential Pressure Distortion Induced by a Centrifugal Compressor’s External Volute

It is well understood that a volute, depending on its operating point, acts either as a nozzle or diffuser. However, the resulting static pressure distortion at diffuser exit is rather considered as side effect and has rarely been investigated systematically in detail. Evidence whether this distortion is amplified or alleviated towards impeller exit is even contradictory in literature. In this work a thorough investigation of aerodynamic volute-impeller interaction is presented. First, a 1D-analysis is carried out in order to understand the fundamental relation between volute matching and pressure distortion. Then, one large external volute, coupled with different impellers, is investigated by means of CFD. These configurations feature different diffuser ratios and blade exit angles, while identical matching ensures comparable conditions. The results reveal that pressure distortion is directly related to the volute’s pressure recovery coefficient. Consequently, at diffuser exit, a local pressure recovery coefficient around circumference can be defined, which is widely independent from the impeller but rather depends on volute geometry and matching. It is this local pressure recovery factor that defines the static pressure distortion at diffuser exit, together with dynamic pressure. In a next step it is analysed, how the resulting pressure distortion evolves towards the impeller. Therefore, stand-alone CFD calculations of impellers around the entire circumference are performed, applying defined pressure distortions at diffuser exit and varying operational conditions carefully. In doing so, fundamental understanding of when distortion is amplified or alleviated towards the impeller is gained.

Assessing the Impact of the Inlet Total Pressure Distortion on the Turbofan Thrust

The paper considers techniques to develop a mathematical model using a method of «parallel compressors». The model is intended to estimate the impact of the air inlet distortion on the primary parameters of the aero-engine. The paper presents rated estimation results in the context of twin spool turbofan design for two typical cruiser modes of flight of the supersonic passenger jet. In estimation the base values σbase and the average values of the inlet ram recovery σave remained invariable. Thus, parametrical calculations were performed for each chosen relative value of the area of low-pressure region.The paper shows that an impact degree of the inlet distortion on the engine thrust for two modes under consideration is essentially different. In other words, if in the subsonic mode the impact assessment can be confined only to taking into account the influence of decreasing average values of the inlet total pressure, the use of such an assumption in the supersonic cruiser mode may result in considerable errors.With invariable values of the pressure recovery factor at the engine intake, which correspond to the speed of flight for a typical air inlet of external compression σbase, and average value σave, a parameter Δσuneven has the main effect on the engine thrust, and degree of this effect essentially depends on a difference between σave and σbase values.

Unsteady Numerical Simulation of Flow in Draft Tube of a Hydroturbine Operating Under Various Conditions Using a Partially Averaged Navier–Stokes Model

The variable energy demand requires a great flexibility in operating a hydroturbine, which forces the machine to be operated far from its design point. One of the main components of a hydroturbine where undesirable flow phenomena occur under off-design conditions is the draft tube. Using computational fluid dynamics (CFD), the present paper studies the flow in the draft tube of a Francis turbine operating under various conditions. Specifically, four operating points with the same head and different flow rates corresponding to 70%, 91%, 99%, and 110% of the flow rate at the best efficiency point (BEP) are considered. Unsteady numerical simulations are performed using a recently developed partially averaged Navier–Stokes (PANS) turbulence model, and the results are compared to the available experimental data, as well as the numerical results of the traditionally used Reynolds-Averaged Navier–Stokes (RANS) models. Several parameters including the pressure recovery coefficient, mean velocity, and time-averaged and fluctuating wall pressure are investigated. It is shown that RANS and PANS both can predict the flow behavior close to the BEP operating condition. However, RANS results deviate considerably from the experimental data as the operating condition moves away from the BEP. The pressure recovery factor predicted by the RANS model shows more than 13% and 58% overprediction when the flow rate decreases to 91% and 70% of the flow rate at BEP, respectively. Predictions can be improved significantly using the present unsteady PANS simulations. Specifically, the pressure recovery factor is predicted by less than 4% and 6% deviation for these two operating conditions. A similar conclusion is reached from the analysis of the mean velocity and wall pressure data. Using unsteady PANS simulations, several transient features of the draft tube flow including the vortex rope and associated pressure fluctuations are successfully modeled. The formation of the vortex rope in partial load conditions results in severe pressure fluctuations exerting oscillatory forces on the draft tube. These pressure fluctuations are studied for several locations in the draft tube and the critical region with highest fluctuation amplitude is found to be the inner side of the elbow.

Influence of Area Distribution With Fixed Trajectory on Serpentine Intake Duct Performance

Performance of intake duct with fixed inlet trajectory and different area distributions have been analyzed using a commercial CFD (Computational Fluid Dynamics) software. The performance have been evaluated for fixed boundary conditions. The area distributions studied are defined by varying cross sectional area at different locations of intake duct by keeping the inlet and exit area same. The performance of the intake ducts are studied in terms of the pressure recovery coefficient, total pressure loss, pressure recovery factor and distortion coefficient in the present work. The motion caused by the change in centerline curvature is analyzed. The objective of the work is to derive a shape of the duct with minimum distortion of the flow and maximum pressure recovery.