Определение адиабатной температуры стенки в высокоскоростных потоках газа с использованием тепловизионной съемки

Evaluating the impact of solid particle temperature on high-speed gas flow using Eulerian–Lagrangian method and machine learning approach

The present study considers spatially resolved surface heat transfer coefficients and adiabatic wall temperatures on a turbine blade tip in a linear cascade under transonic conditions. Five different measurement and processing techniques using infrared thermography are considered and compared. Three transient methods use the same experimental setup, using a heater mesh to provide a near-instantaneous step-change in mainstream temperature, employing an infrared camera to measure surface temperature. These three methods use the same data but different processing techniques to determine the heat transfer coefficients and adiabatic wall temperatures. Two of these methods use different processing techniques to reconstruct heat flux from the temperature time trace measured. A plot of the heat flux versus temperature is used to determine the heat transfer coefficients and adiabatic wall temperatures. The third uses the classical solution to the 1D nonsteady Fourier equation to determine heat transfer coefficients and adiabatic wall temperatures. The fourth method uses regression analysis to calculate detailed heat transfer coefficients for a quasi-steady-state condition using a thin-foil heater on the tip surface. Finally, the fifth method uses the infrared camera to measure the adiabatic wall temperature surface distribution of a blade tip after a quasi-steady-state condition is present. Overall, the present study shows that the infrared thermography technique with heat flux reconstruction using the impulse method is the most accurate, computationally efficient, and reliable method to obtain detailed, spatially resolved heat transfer coefficients and adiabatic wall temperatures on a transonic turbine blade tip in a linear cascade.

This paper focuses on the mechanisms of combustion noise during the accelerating operation of multi-cylinder diesel engines using testing technology for the transient conditions of IC engines. Based on impact factors, such as the gas dynamic load and cylinder pressure oscillations, tests and analysis of the combustion noise during transient and steady-state conditions for different loads are made on four-cylinder naturally aspirated engines, turbocharged engines, EGR-introduced engines, and high pressure common rail engines. The laws of combustion noise difference for the same engine speed and load are researched during transient and steady-state conditions. It is found that during transient conditions, the maximum pressure rise rate and the high frequency oscillation amplitude of the cylinder pressure are all higher than those observed during steadystate conditions for the same engine speed and load. With their joint action, the combustion noise during transient conditions is greater than that during steady-state conditions. Turbocharging is useful in reducing the combustion noise during transient conditions. Turbocharging has a better effect on the control over the combustion noise during transient conditions with a constant engine speed and an increasing torque than in conditions with a constant torque and an increasing engine speed. One of the main reasons for different control effects on the combustion noise is that turbocharging causes different wall temperatures inside combustion chambers. The introduction of the appropriate EGR is helpful in the reduction of the combustion noise during transient conditions. The key to the control of combustion noise with EGR during transient conditions is whether a real-time adjustment to the EGR rate can be made to achieve the optimization of the EGR rates for different transient conditions. By means of analyzing the differences in the combustion noise between the transient and steady-state conditions for different pilot injection controls, we obtain a strategy for controlling the combustion noise during transient conditions with a pilot injection. Compared with the steady-state conditions, a larger pilot injection quantity and a longer interval between the main injection and pilot injection should be selected for transient conditions, and this is verified through tests.

With its low viscosity properties, CO2 has much greater penetration capacity into micro-fractures, and therefore has more potential to create expanded and effective fractures in shales during the hydraulic fracturing process. However, the feasibility of this technique is dependent on the accurate prediction of formation flow characteristics, given the high leak-off of CO2 at deep depths. The aim of this study is therefore to understand the flow behavior of CO2 in deep shale plays. A series of tri-axial permeability tests was conducted under both steady-state and transient conditions. The test results show much lower permeability values for liquid CO2 than gaseous CO2, and the permeability under transient conditions is much lower than that under steady-state conditions, due to the combined effects of the reduced slip-flow effect under low pressures and the temperature variation influence under steady-state conditions. Under steady-state conditions, unstable flow behavior occurred at higher injection pressure (≥9 MPa) possibly due to the fine mineral particle migration and the deposition of small drikold particles, which indicates the serious error in permeability calculation under steady-state conditions. Importantly, a greater than 1 effective stress coefficient (χ) for permeability in tested siltstone was observed, confirming the greater sensitivity of CO2 to pore pressure than confining pressure.

: The effects of localized aerodynamic heating in cylinder expansion gaps positioned in cross flow were investigated in a shock tube. For this study, Mach number and Reynolds number were varied from 1.04 to 1.38 and 5 x 105 to 9 x 105, respectively. The cylinder was instrumented with quick response time thermocouples positioned on the surface of the cylinder, the wall of the gap, and the gap floor. Gap aspect ratios varied from 1.23 to 3.69. Pressure gauges were used to measure wave shock speeds, pressure ratios, and transient pressure conditions. Surface temperatures were measured and converted to heat fluxes using a one-dimensional semi-infinite slab model. Adiabatic wall temperatures were obtained from pressure measurements and ideal gas law relationships. Local nondimensional heat transfer coefficients, Nusselt numbers, were calculated from experimental surface and adiabatic wall temperatures. The present study found a direct dependence on Nusselt number values with Mach number. Peak heating inside the gap was determined to be a function of gap width and location on the cylinder. As gap width was reduced, the location of peak heating on the cylinder varied and Nusselt number values on the floor of the gap dominated. Shock tubes, Aerodynamic heating, Cylinder heat transfer, Heat transfer in gaps, Cylinder in cross flow.

Common gas turbine heat transfer analysis methods rely on the assumption that the driving temperature for heat transfer to a film cooled wall can be approximated by the adiabatic wall temperature. This assumption implies that the gas temperature above a film cooled adiabatic wall is representative of the overlying gas temperature on a film cooled conducting wall. This assumption has never been evaluated experimentally. In order for the adiabatic wall temperature as driving temperature for heat transfer assumption to be valid, the developing thermal boundary layer that exists above a conducting wall must not significantly affect the overriding gas temperature. In this paper, thermal fields above conducting and adiabatic walls of identical geometry and at the same experimental conditions were measured. These measurements allow for a direct comparison of the thermal fields above each wall in order to determine the validity of the adiabatic wall temperature as driving temperature for heat transfer assumption. In cases where the film cooling jet was detached, a very clear effect of the developing thermal boundary layer on the gas temperature above the wall was measured. In this case, the temperatures above the wall were clearly not well represented by the adiabatic wall temperature. For cases where the film cooling jet remained attached, differences in the thermal fields above the adiabatic and conducting wall were small, indicating a very thin thermal boundary layer existed beneath the coolant jet.

The method of energy separation in a high-speed flow proposed by A.I. Leontyev is investigated numerically. The adiabatic compressible gas flow (of a helium-xenon mixture) with a low Prandtl number in a planar narrow duct and a flow with heat exchange in a duct partitioned by a heat-conducting wall are analysed. The temperature recovery factor on the adiabatic wall, degree of cooling the low-speed flow part, temperature efficiency, and the adiabatic efficiency in a duct with heat exchange are estimated. The data are obtained for the first time, which make it possible to compare the efficiency of energy separation in a high-speed flow with the efficiency of similar processes in vortex tubes and other setups of gas-dynamic energy separation.

Enhanced water collection of bio-inspired functional surfaces in high-speed flow for high performance demister

INTRODUCTION This paper presents an analytical and experimental investigation of the convective heat transfer between a cylinder rotating at high speed within a stationary outer cylinder with a small clearance gap. The investigation is the basis of a larger study to determine the convective film coefficients on the unique faces of a four-pole high-speed rotor under development for use within a switched reluctance electric generator. Analytical models for the velocity and temperature distributions of the air in the annular gap are developed. Applying the concepts of high-speed external boundary layer flow, an adiabatic wall temperature is defined that accounts for the effects of viscous heat generation within the gap region. Using these models, convective film coefficients are developed based on the adiabatic wall temperature. The analytical results are compared to experimental data from which the film coefficients were inferred. It is found that the values of Stanton number determined from experimental data are in excellent agreement with values predicted by the theoretical model when the level of shear stress is increased in a manner suggested by experimental windage data. Copyright © 1998 The American Institute of Aeronautics and Astronautics, Inc. All rights reserved. As part of the United States Air Force's More-Electric Aircraft initiative, a gearless, oilless integrated power unit (IPU) is under development for use on jet aircraft. The IPU combines the functions of a conventional auxiliary power unit (APU) and emergency power unit (EPU). Its function is to provide power to the 270 Vdc electrical bus of the aircraft and is being designed to provide a continuous power output of 125 kw. The IPU is turbine powered and comprised of a switched reluctance generator mounted on a common shaft between the compressor discharge and turbine and will operate at speeds up to 55,000 rpm. The generator employs a four-pole rotor with an overall pole-tip to pole-tip diameter of 109.2 mm (4.30 in.). The design clearance between the pole tips and surrounding stator wall is nominally 0.508 1.016 mm (0.020 0.040 in.). At 55,000 rpm, the pole tip speed is 314 m/s and viscous heat generation will clearly be present in the gap region. The generator is air cooled by the discharge-from the turbine compressor. Effective cooling of the rotor and stator is one of the many interrelationships involved in the optimal design of the integrated system. Estimating the convective film coefficient on the unique rotor pole faces is 1 American Institute of Aeronautics and Astronautics Copyright© 1998, American Institute of Aeronautics and Astronautics, Inc. essential for the overall thermal modeling of the generator. The University of Dayton has fabricated experimental test apparatus and developed analysis tools to test the actual rotor geometries at speeds ranging up to 30,000 rpm. Five test rotors of the same cross-section as the proposed rotors for the EPU were manufactured. Each test rotor was uniquely insulated to channel most heat transfer through the rotor pole face of interest. As part of the testing, a smooth cylindrical rotor, referred to as Rotor 6, was fabricated to provide experimental data to be used in validating the analysis of experimental test data. Analysis of the data for Rotors 1 through 5 is in progress; however, analysis of the test data for Rotor 6 has been completed. The following is a presentation of the theoretical model of the velocity and temperature fields in the annular gap between an inner rotating cylinder and outer stationary cylinder and a comparison of the theoretical convective film coefficient to the experimental data for Rotor 6. ANALYTICAL MODEL OF CONVECTTVE FILM COEFFICIENT FOR NONLAMINAR. WALL DRIVEN FLOW WITH VISCOUS HEATING The convective film coefficient was estimated by analyzing the airflow in the annular gap between the rotor and stator surfaces. The gap height is much smaller than the rotor radius so that this flow may be considered as wall driven flow between two flat plates as shown in Figure 1. In Figure 1 the rotor has been illustrated as the lower, stationary surface with heat flux qR transferred from the rotor to the air. The upper surface is shown as the stator surface with heat flux qs — qR + e transferred u(y) Upper surface moves at speed V, u(h) = V u(y), velocity distribution Thickness of viscous sublayer, Stationary lower surface, u(0) = 0

The casing end-wall of a shroudless high-pressure turbine is subject to severe thermal loading. A backwards facing step positioned upstream of the leading edge of the rotor has been shown to reduce the heat flux in this region. The testing has been conducted at fully engine scaled Mach number, Reynolds number and gas-to-wall temperature ratio. Measurements of local heat-flux and static pressure were made using thin-film and semi-conductor gauges respectively. Normalised heat-flux, static pressure, adiabatic wall temperature and heat-transfer coefficient distributions are compared with those from a previously tested plain annulus baseline geometry. The introduction of the casing step has lowered the casing end-wall heat-load. This reduction is associated primarily with a decrease in adiabatic wall temperature on the casing end-wall. Analysis of the time-resolved static pressure distribution, combined with a Computational Fluid Dynamics simulation, has shown that this reduction in adiabatic wall temperature is the result of work extraction from the fluid entrained behind the casing step. The variation of the blade tip loading with upstream guide vane phase has also been reduced.

Energy separation in a channel with permeable wall

Real-time numerical simulations and experimental research for the propagation characteristics of shock waves and gas flow during coal and gas outburst

Discussions of some myths and concerned practices of film cooling research

Review of Filtered Rayleigh Scattering technique for mixing studies in supersonic air flow

Gas atomization uses a high-speed gas flow to impact alloy melt and crush it into small droplets. During this process, the kinetic energy of the high-speed gas flow is transformed into the surface energy of small droplets, and the droplets are dragged and cooled by the gas. In this study, a FeNiCrBSiC alloy was used to investigate the motion and solidification behavior of alloy droplets during gas atomization. A mathematical model of the cooling and solidification process of droplets is modified and used. The initial velocity of the droplets attributed to the breakup by the high-speed gas flow is considered a factor. The results suggest that the velocity difference between the droplet and the gas is appearing to be smaller, indicating that droplets are more likely to collide with each other; as the velocity difference between the droplet and the gas becomes smaller, the heat transfer coefficient decreases. Thus, the solidification process of the droplet needs a longer flight distance; the relation between the cooling rate and the particle size was determined from measured data and empirical formula and model validation was performed.