Inlet Edge Research Articles

管路内絞り部の圧力，流速分布の数値解 絞りのキャビテーションと関連して

The two-and three-dimensional pressure and velocity distributions around restrictors in pipes are numerically obtained by applying the finite volume method with k-e turbulence model. As the numerical method is not applicable to flows with phase change, the results correspond to the fluid with an enough tensile strength. However, for the case of three kinds of orifices whose experimental results have already been reported, the minimum pressure which appears just after the inlet edge of orifices is shown to be able to explain the facility of cavitation occurrence.

Efficiency of welding methods for repairing steam turbine blades and hardening their inlet edges

Efficiency of welding methods for repairing steam turbine blades and hardening their inlet edges

Capillary end effect in a water saturated porous layer

The uni-directional propagation of oil injected into water flowing through a water wetted porous slab of a finite length is investigated. The inlet and outlet edges of the slab are impermeable to the oil flux. Hence, the oil accumulates within the slab, thereby leading to a saturation build-up-capillary end effect. This phenomenon is studied analytically on the basis of a nonlinear equation describing oil-water transport in porous media. A dimensionless criterion is derived, which governs the appearance and relative strength of the capillary end effect. For weak oil-water interfacial tension (large capillary number) and long porous slabs the above effect is not observed and the temporal evolution of the oil saturation is described by the Buckley-Leverett solution. Short porous slabs are found to be almost entirely subjected to the capillary end effect. Intermediate situations are identified and quantitatively described, in which the downstream part of the slab may be divided into two zones: one-characterized by the capillary end effect, and the other being a Buckley-Leverett zone.

Local heat transfer on the entrance segment of a tube with a sharp inlet edge. 2. Correction for the entrance segment under turbulent boundary layer conditions

A correction relation eX=f(Red;X/d) is proposed for the entrance segment, where turbulent flow occurs in a surface boundary layer developing upon completing the transient process. An elevated local heat transfer intensity in a separated flow region beyond a sharp inlet edge is considered to be a consequence of the M-shaped velocity field profile that exists over a substantial length of the entrance segment.

Local heat transfer on the entrance segment of a tube with a sharp inlet edge. 1. Nature and behavior of heat transfer intensity extrema

Experimental results on local heat transfer on the entrance segment of a round smooth tube with a sharp leading edge when Red=(13–110)·103, X/d=0.1–13, which support the previously proposed model for separated flow, are examined. It is shown that under separated flow conditions the usual sequence of flow transitions in a boundary layer for mixed nonseparated flows and Red>104 is still retained. Formulas are obtained for calculating local heat transfer coefficients on a segment where a laminar boundary layer occurs, including cross sections where these coefficients acquire extreme values.

Evaluation of the life and methods of ensuring reliability of large blades of an axial compressor. Report 1

Calculations were carried out to determine the life of a large compressor blade of DIT alloy with a crack at the inlet edge in the root section with the specified probability of nonfailure under the conditions corresponding to the service conditions. Special attention is given to examining the feasibility of producing this blade from VT6S alloy instead of DIT alloy with an allowance made for the mechanical properties of materials, cracking resistance, and service conditions. Investigations were carried out into the cracking resistance characteristics of DIT and VT6S alloys with an allowance made for the statistical properties of the experimental results obtained at temperatures of 363, 293, 173, and 77 K and different stress ratios. The results were then compared. The data obtained in service loading were used to calculate the period of the crack growth in blades of DIT and VT6S alloys at a nonfailure probability of 0.5 and 0.999. Analysis of life calculations showed that D1T alloys are more suitable than VT6S alloys for producing blades of compressors of a wind tunnel.

Possibility of increasing the service life of damaged blades

Results are given of an investigation of the effectiveness of a method of strengthening the working titanium alloy blades of a gas turbine engine compressor. It is established that the proposed strengthening method can lengthen to more than double the service life of damaged blades. In addition it is shown that in these blades, in comparison with nonstrengthened blades, cracks develop in a narrower zone and predominantly on the side of the inlet edge.

Structure of the static pressure field on the entrance length of a pipe with a sharp inlet edge

The three-dimensional static pressure field on the entrance length of a circular pipe with a sharp inlet edge is measured. The field structure, which is characterized by its nonuniformity in the longitudinal and radial directions, is in fairly good agreement with the previously proposed separated flow model and indicates the existence of M-shaped velocity profiles in cross sections of the entrance length.

FINITE ELEMENT ELASTIC-PLASTIC-CREEP AND CYCLIC LIFE ANALYSIS OF A COWL LIP

Results are presented of elastic, elastic-plastic, and elastic-plastic-creep analyses of a test-rig component of an actively cooled cowl lip. A cowl lip is part of the leading edge of an engine inlet of proposed hypersonic aircraft and is subject to severe thermal loadings and gradients during flight. Values of stresses calculated by elastic analysis are well above the yield strength of the cowl lip material. Such values are highly unrealistic, and thus elastic stress analyses are inappropriate. The inelastic (elastic-plastic and elastic-plastic-creep) analyses produce more reasonable and acceptable stress and strain distributions in the component. Finally, using the results from these analyses, predictions are made for the cyclic crack initiation life of a cowl lip. A comparison of predicted cyclic lives shows the cyclic life prediction from the elastic-plastic-creep analysis to be the lowest and, hence, most realistic.

Experimental investigations of an underexpanded jet from a convergent nozzle impinging on a cavity

The influence of the detailed shape of the nozzle exit and the cavity inlet edge on the oscillating flow characteristics are investigated. The experiments show that the shape of the cavity edge considerably influences acoustical and thermal effects as well as the oscillatory mode (screech and regurgitant) switching. The shape of the nozzle exit edge has a minor significance. The screech oscillation mode mechanism and some details of the regurgitant mode are determined from external flow visualization and pressure measurements. Some characteristics of the near flow field induced by an oscillating jet are also obtained.

Flow in the initial segment of a tube with a sharp inlet edge. Comparative analysis

When flow becomes detached in the inlet segments of tubes and channels with sharp leading edges and where the Reynolds numbers exceed 75·103, the displacement of the maximum of the local heat transfer is in agreement with the onset of secondary laminar flow.

Pressure boundary conditions of high-speed thrust bearings.

This paper describes a study on the boundary conditions at the inlet edge of high-speed thrust bearings in a turbulent flow regime, taking into account the inertia effects. The basic lubrication equations in terms of pressure and stream function are solved for finite-width bearings by applying a numerical calculation technique combining control volume integration and Newton-Raphson linearization method. Moreover, an analytical solution is given for infinitely long bearings. Static bearing performance characteristics such as pressure distribution, load-carrying capacity, pressure center and inlet flow rate are calculated for three kinds of inlet boundary conditions in relation to three types of lubrication conditions, namely: the flooded condition, the overflooded condition and the starved condition. Some samples of the numerical results are presented in graphic form, and the relationship between the inlet boundary conditions and static bearing performance is discussed.

Pressure boundary conditions for high speed thrust bearings. 2nd report. Finite width thrust bearings.

This paper describes a study on the boundary conditions at the inlet edge of finite width thrust bearings in a turbulent flow regime, including the fluid inertia effects. The integrated governing equations in terms of pressure and stream functions are solved by a numerical technique combining the control volume integration and the Newton-Raphson iteration method. The static characteristics such as pressure distribution, load carrying capacity, center of pressure and inlet flow rate are obtained for three kinds of inlet boundary conditions in accordance with three types of lubrication conditions. Some sample of numerical results are presented in graphic form and the relationships between the boundary conditions and the static characteristics are discussed.

Pressure boundary conditions for high speed thrust bearings. (1st report Infinitely long thrust bearings)

Three kinds of pressure boundary conditions at the inlet edge of hydrodynamic thrust bearings under turbulent operating conditions including inertia effects are theoretically discussed. The turbulent lubrication equation considering the inertia effects is solved for infinitely long thrust bearings, in which three kinds of pressure boundary conditions are applied at the inlet edge of the bearings in accordance with three types of lubrication conditions, namely : the flooded condition, the overflooded condition and the starved condition ; and an analytical solution for each condition is presented for the plane slider bearings. Sample results are indicated in graphical form and the relationships between three kinds of pressure boundary conditions and the static characteristics of bearings are discussed for a wide range of Reynolds numbers.

The hydrodynamics of a free, liquid jet and their influence on direct contact heat transfer—I Hydrodynamics of a free, cylindrical liquid jet

The present paper is concerned with the hydrodynamics of a free, cylindrical liquid jet and forms the first part of a set of papers on the influence of jet hydrodynamics on direct contact heating. In the present paper the available literature is discussed and special attention is paid to existing differences between the cited authors' conclusions. On the basis of our own experiments the influence of individual variables on the jet hydrodynamics was analysed qualitatively. Correlations, which hold in the investigated area, are proposed. The phenomenon of hysteresis in the case of flow through short nozzles (L/d < 2) having sharp inlet edges was observed.

Effect of thermal cyclings and a corrosive environment on the condition of the surface layer and performance of gas-turbine blades

bility of the heat-resistant heterophase alloy in the intermediate layers [1-5, etc.]. Specifically, such structural instability includes the following effects: a change in the fine structure characteristic of the solid solution of the metal (microstresses and cell dimensions); redistribution of the main alloying elements under the influence of temperature and the formation of new phases; formation of secondary structures due to the reaction of alloying elements with the components of fuel combustion products; recrystallizatio n of the plastically deformed surface layer, etc. The present work investigates the performance of gas turbine blades and the condition of their surface layer under the thermocyclic and corrosive effects of a high-temperature gas stream, including one to which marine salts have been added. The condition of the surface layer of the blades was evaluated by studying changes in the parameters of the fine structure, microstructure, and chemical composition of the surface layers of the blade material after tests on a gasdynamic stand. Structure was studied by metallographic and x-ray diffraction methods and the method of x-ray microspectroscopy. In the x-ray diffraction analysis, we studied specimens cut from the inlet edge of the blades at different stages of thermocycling (service), using a DRON-2 diffractometer and copper K~-radiation. Microdistortions and regions of coherent scattering (RCS) were calculated using the method of approximation in [i] on an electronic digital computer. The content of chemical elements was determined on a "CAMECA" microanalyzer by scanning the specimen under an electron probe from the middle to the surface. The element concentrations shown below were computed with allowance for correction factors on an electronic digital computer. The performance of gas-turbine blades was studied on the gasdynamic stand of the Institute of Strength Problems of the Ukrainian Academy of Sciences in a thermocyclic, corrosive high-temperature stream of fuel combustion products, including a stream containing marine salts. The experimental method and equipment were described in [2]. We tested models of GTE rotor blades made of alloys ~P220 and ~I827. The tests were conducted with a cyclic change in the temperature of the gas stream within the range 250I150~ Here, the temperature of the metal of the inlet edge of the blades changed within the range 920-440~ Heating time in each cycle was 5 sec, cooling time i0 sec. To simulate the conditions of GTE service in sea water, we added to a gas stream of kerosine combustion products synthetic seawater with a content of 1 mg of salts per 1 m s air. For comparison, we also conducted tests without marine salts in the gas stream.

The performance characteristics of Borda inlet air flowmeters

The characteristics of Borda inlets when used as flowmeters are investigated, and the parameters which have to be taken into account when predicting the calibration coefficient (commonly referred to as the 'discharge' coefficient) of any particular device are determined. Standardised positions for locating the pressure tappings are proposed, and the variation of discharge coefficient with Borda diameter and relative thickness of the inlet edge is established. The modified method of using a Borda inlet which is presented avoids the need to use any corrections for compressibility effects, but the relationships found between discharge coefficient and the various parameters have been obtained for tests in air only, and so should not be used for any compressible fluid with an appreciably different specific heat ratio.

Computation of the two-dimensional viscous incompressible fluid flow with separation at the nlet edge around a cascade

A complex flow consisting of an outer inviscid stream, a dead-water separation domain, and a boundary layer, which interact strongly, is formed in viscous fluid flows with separation at the streamlined profile with high Re numbers. Different jet and vortex models of separation flow are known for an inviscid fluid; numerical, asymptotic, and integral methods [1–3] are used for a viscous fluid. The plane, stationary, turbulent flow through a turbine cascade by a constant-density fluid without and with separation from the inlet edge of the profile and subsequent attachment of the stream to the profile (a short, slender separation domain) is considered in this paper.

The Effect of Edge Sharpness on the Discharge Coefficient of an Orifice

The effect of inlet edge roundness on the discharge coefficient of an orifice plate is studied experimentally. Several methods for measuring edge roundness are discussed and applied. An optical method in particular is shown to provide reliable measurements of edge roundness. Flow results are summarized in terms of radius of curvature by the empirical equation ΔCD/CD = 0.85 ln (rk/d × 103) + 1.74.

Reducing abrasive wear in hydraulic equipment

1. The type of hydroabrasive wear of a soil pump depends on the size, hardness, and roundness of the particles of the pumped materials. When pumping gravelly soil, the most intense wear is primarily on the inlet edges of the rotor blades and the casing; when pumping sandy materials, the greatest wear is at the outlet edges of the rotor blades and the armor disks. 2. It is inefficient to use a worn soil pump owing to the reduction in its energy indices: the soil output is reduced by 30% or more, the pressure head falls, and the power consumption correspondingly increases. 3. Various measures to reduce the rate of wear of a soil pump enable us to improve the use factor of the equipment during hydromechanization by 0.5–5%, to increase its output, to reduce power consumption, and finally to cut down the cost of the work. Experiments have shown that the service lives of soil pumps can be increased by increasing the wear resistance of the materials used to make them — by building up compounds with hard wear-resistant alloys, by rubberizing the working surfaces, by using wear-resistant coatings, by heat treatment of the components, and by using pump designs which ensure that the various elements in the flow duct will wear equally. 4. Experience at the Gidromekhanizatsiya Trust of the Ministry of Energy of the USSR has shown that at present the greatest reduction in hydroabrasive wear can be achieved by using rotors cast from steel 30KhNML.