Inducer Blade Research Articles

Experimental and Computational Results From the NASA Lewis Low-Speed Centrifugal Impeller at Design and Part-Flow Conditions

The NASA Lewis Low-Speed Centrifugal Compressor (LSCC) has been investigated with laser anemometry and computational analysis at two flow conditions: the design condition as well as a lower mass flow condition. Previously reported experimental and computational results at the design condition are in the literature (Hathaway et al., 1993). In that paper extensive analysis showed that inducer blade boundary layers are centrifuged outward and entrained into the tip clearance flow and hence contribute significantly to the throughflow wake. In this report results are presented for a lower mass flow condition along with further results from the design case. The data set contained herein consists of three-dimensional laser velocimeter results upstream, inside, and downstream of the impeller. In many locations data have been obtained in the blade and endwall boundary layers. The data are presented in the form of throughflow velocity contours as well as secondary flow vectors. The results reported herein illustrate the effects of flow rate on the development of the through flow momentum wake as well as on the secondary flow. The computational results presented confirm the ability of modern computational tools to model the complex flow in a subsonic centrifugal compressor accurately. However, the blade tip shape and tip clearance must be known in order to properly simulate the flow physics. In addition, the ability to predict changes in the throughflow wake, which is largely fed by the tip clearance flow, as the impeller is throttled should give designers much better confidence in using computational tools to improve impeller performance.

Development of an Axial Flow Ventricular Assist Device: In Vitro and In Vivo Evaluation

A collaborative effort between Baylor College of Medicine and NASA/Johnson Space Center is underway to develop an axial flow ventricular assist device (VAD). We evaluated inducer/impeller component designs in a series of in vitro hemolysis tests. As a result of computational fluid dynamic analysis, a flow inducer was added to the front of the pump impeller. According to the surface pressure distribution, the flow inducer blades were connected to the impeller long blades. This modification eliminated high negative pressure areas at the leading edge of the impeller. Comparative studies were performed between inducer blade sections that flowed smoothly into the impeller blades (continuous blades) and those that formed discrete separate pumping sections (discontinuous blades). The inducer/impeller with continuous blades showed significantly (p < 0.003) lower hemolysis with a normalized index of hemolysis (NIH) of 0.018 +/- 0.007 g/100 L (n = 3), compared with the discontinuous model, which demonstrated an NIH of 0.050 +/- 0.007 g/100 L (n = 3). The continuous blade model was evaluated in vivo for 2 days with no problems. One of the pumps evaluated ran for 5 days in vivo although thrombus formation was recognized on the flow straightener and the inducer/impeller. As a result of this study, the pump material was changed from polyether polyurethane to polycarbonate. The fabrication method was also changed to a computer numerically controlled (CNC) milling process with a final vapor polish. These changes resulted in an NIH of 0.0029 +/- 0.0009 g/100 L (n = 4), which is a significant (p < .0001) value 6 times less than that of the previous model.(ABSTRACT TRUNCATED AT 250 WORDS)

Aspects instationnaires de poches de cavitation : Mesures de pressions et films rapides simultanés

Click to increase image sizeClick to decrease image sizeThree experiments have been made to analyse unsteadiness of cavitation phenomena on a Vulcain-type inducer : 1) water simulations on inducer, 2) hydrofoil-type and 3) venturi-type 2D test-sections which modelize the suction side of the inducer blades. In the hydrofoil case, vapor clouds appear periodically. By contrast, the venturi-type test rig does not present any periodic behaviour. In the inducer, another unsteady configuration appears : a cavity pattern moves from blade to blade in the same direction as the rotation.

An analysis of pump cavitation damage

The cavitation assessment for the space shuttle main engine high pressure oxidizer turbopump is documented. A model of the flow through the pump was developed. Initially, a computational procedure was used to analyze the flow through the inlet casing including the prediction of wakes downstream of the casing vanes. From these flow calculations, cavitation patterns on the inducer blades were approximated and the damage rate estimated. The model correlates the heavy damage on the housing and over the inducer with unsteady blade surface cavitation. The unsteady blade surface cavitation is due to the large incidence changes caused by the wakes of the upstream vanes. Very high cavitation damage rates are associated with this type of cavitation. Design recommendations for reducing the unsteady cavitation include removing the set of vanes closest to the inducer and modifying the remaining vanes.

Flow in the Inducer of a Centrifugal Compressor Measured With a Laser Velocimeter

The flow field in the inducer of a high-pressure-ratio centrifugal compressor has been measured with a laser-2-focus velocimeter (L2FV) at two flow rates that were on each side of the apparent inducer-stall limit at 70 percent speed. The limit was determined based on the pressure pattern between inducer blades along the shroud. The measured time-mean velocity distribution is compared with the prediction based on an inviscid quasi-three-dimensional flow analysis and the viscous effects are clarified. Furthermore, the nature of flow unsteadiness is discussed on the basis of the L2FV data. Using the observed data it is concluded that the inducer works well even at the apparent inducer-stall condition.

An Analysis of Three-Dimensional Flow in a Centrifugal Compressor Impeller

This paper presents detailed results of the three-dimensional kinematic flow detail in a centrifugal compressor impeller of common form with inducer and straight radial blade tip sections. The calculation method, which is inviscid and is reported elsewhere, shows the development of a passage vortex in a sense counter to that of blade rotation, initiated in the inducer and disappearing as the flow becomes radial. This vortex unloads the blade shroud sections and combined with slip at the blade tips, produces a jetwake velocity distribution at the blade passage exit. General features of the calculation are at variance with two-dimensional calculations but are in agreement with the experimental results of other workers.

Three-Dimensional Flow Field in Rocket Pump Inducers—Part 2: Three-Dimensional Viscid Flow Analysis, and Hot Wire Data on Three-Dimensional Mean Flow and Turbulence Inside the Rotor Passage

This paper reports the measurement and prediction of the three-dimensional flow field in an axial flow inducer operating at a flow coefficient of 0.065 with air as the test medium. The experimental investigations included measurement of the blade static pressure and blade limiting streamline angle, and measurement of the three components of mean velocity, turbulence intensities and turbulence stresses at locations inside the inducer blade passage utilizing a rotating three-sensor hot-wire probe. Analytical investigations were conducted to predict the three-dimensional inviscid flow and to approximately predict the three-dimensional viscid flow by incorporating the dominant viscous terms into the exact equations of motion in rotating coordinate system. Radial velocities are found to be of the same order as axial velocities and total relative velocity distributions indicate a substantial velocity deficiency near the tip at mid-passage. High turbulence intensities and turbulence stresses are concentrated within this core region. Evidence of boundary layer interactions, blade blockage effects, radially inward flows, annulus wall effects and back-flows are all found to exist within the long, narrow passages of the inducer, emphasizing the complex nature of inducer flow which makes accurate prediction of the flow behavior extremely difficult.

Internal Streamline Flow Analysis for Turbopump Inducers under Cavitating and Noncavitating Conditions

Hydrodynamic internal streamline flow analysis for turboprop inducer blades under cavitating and noncavitating conditions

Stress and Vibration Analysis of Turbopump Inducer Blades by Finite Elements

This paper discusses the formulation of stress and vibration analysis programs for use on rocket engine turbopump inducer blades. The analytical model is based on the matrix displacement method using discrete, flat triangular elements to define the blade surface. The stress program calculates stress magnitude and distribution caused by pressure loading and centrifugal forces. The vibration program calculates natural frequencies and distribution of relative displacements and stresses at resonance for a nonrotating inducer blade. The capabilities of the computer programs are demonstrated, and experimental static and operational test data indicate that the programs are capable of predicting frequencies, points of maximum stress, and maximum stress levels.

Typical Performance Characteristics of Gas Turbine Radial Compressors

If the peak impeller and diffuser efficiencies are prescribed, it is found that the characteristics of high-speed radial compressors with straight radial blades are basically functions of the inducer and diffuser throat areas. Estimated characteristics for twenty-seven compressor geometries are presented to indicate the effects of inducer blade angle, diffuser throat to impeller inlet area ratio, and impeller tip to inducer RMS diameter ratio. The probable location of compressor surge as influenced by inducer and diffuser blade stalling is discussed, and comparisons of estimated and test compressor characteristics are given.