Methodology and Experience of Primary Design of a Transonic Axial Compressor

The work presents the main provisions underlying the program for axial compressors calculation anddesign. The calculation of head losses and grids deflection capacity is based on the formulas of A. Komarov. Themodel contains empirical coefficients, values of which are selected during verification of the program based onthe tests results of multistage compressors and compressor stages. The main equations and algorithm for pressuresand velocities calculation under the radial equilibrium condition are presented. The use of computer programsbased on these models in the design of a 4-stage gas turbine engine compressor of moderate power with a totalpressure ratio of 3.2 and a given velocity is shown. For the first compressor stage, two variants with differentflow coefficients were compared. Variant #1 is designed with the classic recommendation to approach the samemechanical gas energy at the exit of the stage along the radius. Variant #2 is designed for a smaller flowcoefficient, but in order to ensure radial equilibrium, it was necessary to introduce a significant unevenness ofmechanical energy supply along the radius. Due to the lower kinetic energy, variant 2 has a 1.9% higher stageefficiency. Despite the fact that the loss coefficients of the blade devices are lower for variant #1. The questionremains as to how much the unavoidable mixing losses of variant #2 will reduce its efficiency in the process ofgas mechanical energy equalizing.

Detached eddy simulations for high speed axial flow fuel pumps with swept and straight blade impellers

Purpose High speed axial flow pumps are widely used in aircraft fuel systems. Conventional axial flow pumps often generate radial secondary flows at partial-load conditions which influence the flow structure and form a “saddle-shaped” region in the Q-H curve that can destabilize the operation. Thus, the “saddle-shaped” Q-H region must be eliminated. The paper aims to discuss these issues. Design/methodology/approach The swept stacking method is often used for radial flow control in turbo-machinery impeller blade design. Hence, this study uses the swept stacking method to design a high speed axial flow pump. The detached eddy simulation method and experiments are used to compare the performance of a swept blade impeller in a high speed axial fuel pump with the original straight blade impeller. Both the pump performance and internal flow characteristics are studied. Findings The results show separation vortices in the impeller with the straight blade design at partial-load conditions that are driven by the rotating centrifugal force to gather near the shroud. The swept geometry provides an extra force which is opposite to the rotating centrifugal force that creates a new radial equilibrium which turns the flow back towards the middle of the blade which eliminates the vortices and the “saddle-shaped” Q-H region. The swept blade impeller also improves the critical cavitation performance. Analysis of the pressure pulsations shows that the swept blade design does not affect the stability. Originality/value This study is the initial application of swept blades for axial flow liquid pumps. The results show how the swept stacking changes the radial equilibrium of the high density, high viscosity flow and the effects on the mass transfer and pressure pulsations. The swept blade effectively improves the operating stability of high speed fuel pumps.

Drained and undrained analyses of cylindrical cavity contractions by bounding surface plasticity

This paper develops a rigorous semi-analytical approach for drained–undrained cylindrical cavity contraction problems in bounding surface elastoplastic geomaterials. For undrained situations, the effective radial, tangential, and vertical component stresses can be solved directly from the constitutive governing differential equations as an initial value problem, the excess pore pressure subsequently being determined from the radial equilibrium equation. In contrast, for the drained case the Eulerian radial equilibrium equation must be first transformed into an equivalent one in a Lagrangian description via the introduction of an auxiliary variable, then solved together with the elastoplastic constitutive relation for the three stress components as well as the specific volume. It is observed that during drained–undrained contraction processes, plastic deformations occur immediately as a direct result of employing the bounding surface model, so outside the cavity there exists no purely elastic zone. The computed stress distributions and in particular the stress path prediction through an example analysis capture well the anticipated elastoplastic and failure behaviour of the geomaterials surrounding the cavity. The validity and accuracy of the proposed semi-analytical elastoplastic solutions are justified through comparison with ABAQUS numerical results, and their applicability to the tunnel excavation and wellbore drilling problems is also demonstrated.