Outlet Static Pressure Research Articles

Research on Flow Characteristics of Supercritical CO2 Axial Compressor Blades by CFD Analysis

A supercritical CO2 gas turbine of 20MPa is suitable to couple with the Na-cooled fast reactor since Na - CO2 reaction is mild at the outlet temperature of 800K, the cycle thermal efficiency is relatively high and the size of CO2 gas turbine is very compact. In this gas turbine cycle, a compressor operates near the critical point. The property of CO2 and then the behavior of compressible flow near the critical point changes very sharply. So far, such a behavior is not examined sufficiently. Then, it is important to clarify compressible flow near the critical point. In this paper, an aerodynamic design of the axial supercritical CO2 compressor for this system has been carried out based on the existing aerodynamic design method of Cohen1). The cycle design point was selected to achieve the maximum cycle thermal efficiency of 43.8%. For this point, the compressor design conditions were determined. They are a mass flow rate of 2035kg/s, an inlet temperature of 308K, an inlet static pressure of 8.26MPa, an outlet static pressure of 20.6MPa and a rotational speed of 3600rpm. The mean radius was constant through axial direction. The design point was determined so as to keep the diffusion factor and blade stress within the allowable limits. Number of stages and an expected adiabatic efficiency was 14 and 87%, respectively. CFD analyses by FLUENT have been done for this compressor blade. The blade model consists of one set of a guide vane, a rotor blade and a stator blade. The analyses were conducted under the assumption both of the real gas properties and also of the modified ideal gas properties. Using the real gas properties, analysis was conducted for the 14th blade, whose condition is remote from the critical point and the possibility of divergence is very small. Then, the analyses were conducted for the blade whose conditions are nearer to the critical point. Gradually, divergence of calculation was encountered. Convergence was relatively easy for the modified ideal gas properties. Main output of calculation is a value of the mass flow rate, which was larger than the design value. However the discrepancy of mass flow rates between CFD and design reduced if the 3-dimensional effects are taken into consideration. Absolute velocity distributions, relative velocity distributions and static pressure distributions surrounding rotor blade and stator blade were obtained. The characteristics of these distributions were consistent with those of the fundamental theory and these analyses were justified.

High Speed Inlet Stage for an Advanced High-Pressure Ratio Core Compressor: Numerical Flow Field Prediction and Verification

NASA rotor 37 is among the most popular rotors that have been manufactured to date. It was designed and tested in early 1980’s by Reid and Moore at NASA Glenn Research Center. It consists of 36 blades with multiple arc profiles, and was designed for compressors with compression ratio of 2.05 at mass flow rate of 20.19 kg/s. Also, it was tested in isolation with circumferentially uniform inlet flow so that the flow through it should be steady apart from any effects of passage to passage geometry variation, and mechanical vibration. As such it represents the simplest possible type of test for a real challenge to 3D viscous flow solvers because chock wave-boundary layer interaction is strong and the effects of viscosity are dominate in determining flow deviation and hence pressure ratio. Computational fluid dynamics (CFD) predictions were obtained by ANSYS-CFX 11.0 with k- turbulence model, and were compared with experimental data which has been taken by NASA. The code predictions (with a uniform and spanwise varying outlet static pressure) show good agreement with respect to measured overall performance characteristic, averaged pitchwise distributions, and averaged spanwise distributions. So, the code now is verified to use with the turbulence model, for farther calculation of turbomachinery. Specially, compressors, compressors blades, and compressors cascade.

Flow at the Centrifugal Pump Impeller Exit With Circumferential Distortion of the Outlet Static Pressure

The effects of circumferential outlet distortion of a centrifugal pump diffuser on the impeller exit flow were investigated. A fence with sinusoidal width variation was installed at the vaneless diffuser exit. The flow field was measured at the impeller exit with and without the fence, using a hot film probe and an unsteady pressure sensor. Flow parameters varied with the circumferential position and the mean flow parameters plotted against the local flow rate at each circumferential position showed loops along the quasi-steady curves, which were obtained from the result without the fence. Simple theoretical calculations were used to predict the velocity components at the impeller exit with the relative flow angle or total pressure assumed. Good result was obtained when the relative flow angle was assumed to vary quasi-steadily, not constant with the local flow rate. The radial velocity was also reasonably predicted when the total pressure was assumed to vary quasi-steadily. A simple method is proposed to predict the impeller exit flow with downstream blockage in two-step sequence: the first step deals with the diffuser alone to obtain static pressure distribution at the diffuser inlet, while the second step deals with the impeller alone to obtain velocity components distribution at the impeller exit.

A Novel Two-Dimensional Viscous Inverse Design Method for Turbomachinery Blading

This paper presents a novel iterative viscous inverse design method for turbomachinery blading. It is made up of two steps: the first one consists of an analysis by means of a Navier-Stokes solver; the second one is an inverse design by means of an Euler solver. The inverse design resorts to the concept of permeable wall, and recycles the ingredients of Demeulenaere’s inviscid inverse design method that was proven fast and robust. The re-design of the LS89 turbine nozzle blade, starting from different arbitrary profiles at subsonic and transonic flow regimes, demonstrates the merits of this approach. The method may result in more than one blade profile that meets the objective, i.e., that produces the viscous target pressure distribution. To select one particular solution among all candidates, a target mass flow is enforced by adjusting the outlet static pressure. The resulting profiles are smooth (oscillation-free). The design of turbine blades with arbitrary pressure distribution at transonic and supersonic outflow illustrates the correct behavior of the method for a large range of applications. The approach is flexible because only the pitch chord ratio is fixed and no limitations are imposed on the stagger angle.

Two-Dimensional Analysis for Non-Equilibrium Homogeneously Condensing Flows through Steam Turbine Cascade.

A computational technique for the two-dimensional non-equilibrium homogeneously condensing flows through steam turbine cascades is presented. The fundamental equations of compressible wet steam flows are descretized based on the TVD scheme and following thermodynamic assumptions. 1) The gas phase is an ideal gas. 2) A liquid phase consists of droplets whose radii are in the order of 10-6m or less, thereby, the wet steam is a homogeneous fluid. 3) A gas-liquid phases are changed by the homogeneous nucleation and growth of the existing droplets, which are described by the classical nucleation theory. In this theory, a driving force of a phase change is a degree of supercooling. The described assumptions are valid for the flow through the low-pressure stage of the steam turbines. Flow through the moving blades for a low-pressure steam turbine is calculated. The calculated pressure distributions on the blade surface agree well with experimental data. The influences of both the degree of inlet supercooling and the ratio of the inlet total pressure to outlet static pressure on the blade performance, mass flow, flow angle, energy loss are studied.

Three-Dimensional Unsteady Flow and Forces in Centrifugal Impellers With Circumferential Distortion of the Outlet Static Pressure

This paper describes the numerical investigation of the centrifugal impeller response to downstream static pressure distortions imposed by volutes at off-design operations. An unsteady three-dimensional Euler solver with nonreflecting upstream and down-stream boundary conditions and phase-lagged periodicity conditions is used for this purpose. The mechanisms governing the unsteady flow field are analyzed. A parametric study shows the influence of the acoustic Strouhal number on the amplitude of the flow perturbations. Radial forces calculated on backward leaned and radial ending centrifugal impellers show nonnegligible influence of the impeller geometry.

A Theoretical Model for Rotating Stall in the Vaneless Diffuser of a Centrifugal Compressor

A theoretical model for rotating stall in the vaneless diffuser of a centrifugal compressor is presented. It consists of a time-evolutive calculation of the strong interaction between the inviscid flow core and the unsteady boundary layers along the walls. It is shown that, depending on the diffuser geometry and the diffuser inlet flow angle, a transient perturbation of the outlet static pressure will generate a rotating flow pattern, if the periodicity of this perturbation corresponds to the experimentally observed number of cells. The relative rotational speed and the phase relation between the velocity and the flow angle variations are also in agreement with experimental data.

The Choking Pressure Ratio of a Critical Flow Venturi

The critical flow venturi has many important applications in the measurement and control of gas flow. In many of these applications, it is desirable to minimize the pressure loss required to maintain critical flow conditions. The performance of the venturi may be characterized by the ratio of outlet static pressure to inlet total pressure just sufficiently small to produce critical flow. This ratio is called choking pressure ratio (CPR). The optimization of diffusers for critical flow Venturis is discussed and suggestions for designs practice are presented. Test results are given for six different diffuser configurations, and a comparison is made with data on 11 configurations from other investigators. This work was done under contract to the National Aeronautics and Space Administration—Marshall Space Flight Center. It is shown that, for the small divergence angles considered, a simply defined diffuser effectiveness parameter is approximately independent of flow conditions and may be used to predict choking pressure ratio. Even very short diffusers greatly improve performance, and, for longer diffusers, critical flow can be maintained at total pressure losses of 5 percent.