Circumferential Non-uniformity Research Articles

Boundary Layer and Formation of Peripheral Nonuniformity in a Turbine Scroll.

A detailed experimental investigation was carried out to examine the three-dimensional boundary layer characteristics in a radial inflow turbine scroll. Some basic flow phenomena and growth of secondary flow were also investigated. In the inlet region of the scroll, the incoming boundary layer begins to assume a skewed nature, namely the radially inward secondary flow caused by the radial pressure gradient. From the inlet region to one-third of the scroll circumference, the secondary flow increases largely that most of the low-momentum fluid in the incoming boundary layer is transported to the nozzle region. The succeeding elimination of the low-momentum fluid in the boundary layer suppresses growth of the boundary layer further downstream, where the boundary layer shows a self-similar velocity profile. The distributions of the boundary layer properties in the scroll correspond well to those of the flow properties at the nozzle. The behavior of the boundary layer in the scroll is found to affect the circumferential nonuniformity of the nozzle flow field.

Thermal and stress analysis of the first wall with asymmetrically heated non-circular coolant channels

Abstract Temperature and thermal stress distributions for a first wall with non-circular coolant channels are calculated without using an empirical heat transfer coefficient. The energy coolant and heat conduction equation are solved simultaneously. The flow is assumed to be laminar; an approximate extension is made to the turbulent flow. The results indicate that the circumferential non-uniformity of the heat transfer coefficient causes thermal stresses that are higher than those predicted by an empirically determined average heat transfer coefficient. The effects of wall thickness and the shape of the coolant channel are discussed.

Investigation, optimization, and calculation of the outlet arrangements of centrifugal compressors

Models were constructed for making a parametric determination of efficient outlet arrangements for centrifugal compressors which calculate the head losses based on where those losses occur and on their physical nature. The losses were located in the spiral channels, in the delivery channels, and on the lips of the scroll, and included boundary layer friction losses, secondary losses caused by flows in the meridonial plane, inductive losses caused by radial pressure gradients, shock losses around the scroll lips, and losses in the discharge header caused by friction and expansion in the flow. The non-coaxial outlet arrangement was preferred due to its lower level of circumferential flow nonuniformity. Its more uniform flow structure gave it a higher operating efficiency over a wide range of operating conditions of the final stage and a loss coefficient 1.3 to 1.5 times smaller than for annular collection chambers. Tests showed that non-coaxial scrolls were suitable for all final stages regardless of impeller and diffuser type.

Unsteadiness of pressure distribution and cavitation inception on the impeller blades of a centrifugal pump.

Pressure distribution and cavitation inception near the inlet region of an impeller passage of a centrifugal pump were examined experimentally. Both at flow rates lower and higher than normal, the pressures on the blade surface of the impeller fluctuated nearly periodically with its circumferential position due to the non-uniform pressure distribution of the volute and the presence of the dividing ridge of the volute. From the measured pressure distributions on the blade surface at a fixed circumferential position, the pressure fluctuations were also found to be caused, especially at low flow rates, by turbulent fluctuations including the separation of flow from the blade surfaces. The quasi-periodic changes in the pressure distribution caused circumferential non-uniformity of the cavitation occurrence near the cavitation inception and effects of the pressure fluctuations on desinentcavitation number were found to be noticeable at a low flow rate.

An experimental investigation of blade element theory for wind turbines. Part 1. Mean flow results

This paper describes an investigation of blade element theory, which is commonly used to describe the flow through wind turbine blades. A two-bladed model turbine was shrouded by a constant-diameter pipe. The tip clearance was sufficiently small to minimise and localise the tip clearance losses. By passively heating the wake of one of the turbine supports, it was found that supports did not produce any significant circumferential non-uniformity in the mean axial and circumferential velocities. These velocities were measured using a conventional three-hole yawmeter and an X-probe hot-wire anemometer. The agreement between the two methods was good. The turbine's power output was also determined by two independent methods; again with good agreement. The major finding was that blade element theory underestimated the power contribution as a function of radius wherever the local angle of attack exceeded the angle that gives the maximum lift/drag in two-dimensional flow. Several possible causes of the discrepancy are discussed.

The Effects of Non-Uniformity and Turbulence of Flow on Hydrodynamic Characteristics of Propeller

It is recently noticed that the non-uniformity of flow brings some deviation of the relative rotative efficiency from the unit and the difference of the effective wake factor from nominal one. The investigations are expected to enter in more details either experimentally or theoretically. The present paper is the report of the experiments and analysis works about the hydrodynamic characteristics of the model propeller acting in the wake flow of the alternate mesh screens of different patterns, such as some circumferential non-uniform wakes of the cos nθ function mode, a radial non-uniform wake and homogeneous wakes.The measurements of velocity fields of cos nθ mode have shown the well correlation of the intensity of turbulence with the shear rate of the velocity profile along the circumference. From the results of the performance tests of the propeller behind the one or two uniform meshes screen, it has been found that the influence of turbulence of flow reduces the low Reynolds number effect of the model propeller. Accordingly, the characteristics of the model propeller in the wake of the two uniform meshes screen has been offered to apply to the analysis of the self-propulsion factor at any low Reynolds no.It has been shown that the circumferential non-uniformity of the cos nθ mode, where n≤6, raises the efficiency of the propeller higher than that of the open condition, that is the high relative rotative efficiency over the unit. The results of analysis of data based on some theoretical considerations have allowed us to conclude that the relative rotative efficiency responds to the circumferential non-uniformity of flow nonlinearly and quasi-stationarily.

Account of Film Turbulence for Predicting Film Cooling Effectiveness in Gas Turbine Combustors

The paper deals with a small but important part of the overall gas turbine engine combustion system and continues earlier published work on turbulence effects in film cooling to cover the case of film turbulence. Film cooling of the gas turbine combustor liner imposes certain geometric limitations on the coolant injection device. The impact of practical film injection geometry on the cooling is one of increased rates of film decay when compared to the performance from idealized injection geometries at similar injection conditions. It is important to combustor durability and life estimation to be able to predict accurately the performance obtainable from a given practical slot. The coolant film is modeled as three distinct regions, and the effects of injection slot geometry on the development of each region are described in terms of film turbulence intensity and initial circumferential non-uniformity of the injected coolant. The concept of the well-designed slot is introduced and film effectiveness is shown to be dependent on it. Only slots which can be described as well-designed are of interest in practical equipment design. A prediction procedure is provided for well-designed slots which describes growth of the film downstream of the first of the three film regions. Comparisons of predictions with measured data are made for several very different well-designed slots over a relatively wide range of injection conditions, and good agreement is shown.

Small Perturbation Analysis of Nonuniform Rotating Disturbances in a Vaneless Diffuser

The behavior of the distorted flow discharged from a centrifugal impeller within a vaneless diffuser is examined theoretically by assuming small disturbances to a main flow. The inlet static pressure distribution is found in the calculation and allowance is made for circumferential nonuniformity in the relative flow angle. The flow is treated as incompressible and inviscid. The analysis shows that the decay of irrotational disturbances is more rapid with increasing disturbance wave number (e.g. more impeller blades) and the effect of the main flow condition on this behavior is very small. With rotational disturbances, however, the decay is slower than in the irrotational case and the effect of wave number is less. However, the phase angle between radial and tangential velocity fluctuations is found to have a strong influence on the decay processes for rotational disturbances. The present small perturbation theory is compared with the well-known Dean and Senoo theory which assumes that the relative flow angle is circum ferentially uniform. The comparison shows that the present theory predicts results very similar to the Dean and Senoo theory for impellers with large blade numbers (>20). For small numbers of blades the large circumferential nonuniformity in relative flow angle, appears at smaller radii and the inaccuracy of the Dean and Senoo theory becomes pronounced.

Circumferential nonuniformity of radiational swelling in shells of peripheral fuel elements in a fast reactor

Circumferential nonuniformity of radiational swelling in shells of peripheral fuel elements in a fast reactor

Circumferentially nonuniform ship propeller inflow

The effect of the circumferential non-uniformity of the thrust distribution on the propeller inflow is quantitatively investigated in the present paper: expressions are derived for the velocity potential and for various components of the inflow veloc