Volute Geometries Research Articles

Investigation of a Novel Turbine Housing to Produce a Nonuniform Spanwise Flow Field at the Inlet to a Mixed Flow Turbine and Provide Variable Geometry Capabilities

Abstract Automotive engine downsizing has placed an increased focus on the ability of the turbocharger to provide adequate boost levels across the full engine operating range. To achieve the desired levels of turbocharger performance, the turbine must be capable of operating effectively at the intended design point and also at off-design conditions. Mixed flow turbines (MFTs) provide a potential method to improve performance at off-design conditions and during transient engine operation. A unique feature of an MFT is the spanwise variation of incidence angle at the rotor leading edge. This results in additional flow separation from the blade suction surface near the hub under a wide range of operating conditions. The flow separation generates additional loss and has a detrimental impact on turbine performance. A novel design of a turbine volute similar to a conventional twin-entry turbine volute was examined. The novel turbine volutes were designed to produce a spanwise variation in flow conditions at the rotor inlet. The primary objective was to reduce the incidence angle and increase the mass flowrate at the hub side of the passage relative to the shroud side, as it has previously been identified that this can be beneficial for MFT performance. A number of different volute geometries were examined by numerical analysis to determine the impact of key parameters on turbine performance. The results indicated that generating a suitable spanwise flow distribution could produce a moderate improvement in turbine efficiency at off-design operating conditions. The novel volute design also provided a means of achieving a degree of variable geometry operation to further improve off-design performance. Turbine performance was examined under the variable geometry operation and an improvement in turbine power output at low-speed, off-design conditions was achieved. This was analogous to operating with a conventional pivoting vane variable geometry system and had the potential to benefit performance during transient engine operation.

Multi-Objective Genetic Algorithm Assisted by an Artificial Neural Network Metamodel for Shape Optimization of a Centrifugal Blood Pump.

A centrifugal blood pump is a common type of the pump used as a left ventricular assist device (LVAD) in the medical industries. The reduction of the LVADs hemolysis level to reduce the blood damage is one of the major concerns in designing of such devices. Also, the enhancement of the LVADs efficiency to decrease the battery size is another design requirement. The blood damage critically depends on the state of the blood being pumped. Besides the blood state, the blood damage also depends on the pump impeller and volute geometries. In this research, a multi-objective optimization of a centrifugal blood pump is performed. A complete 3D-optimization platform is established for both impeller and volute of a centrifugal blood pump consisting of parametric modeling, automatic mesh generation, computational fluid dynamics (CFD) simulation, and optimization strategy. A vast number of cases with various impeller and volute shapes are numerically simulated. Three different metamodels are created using artificial neural networks (ANNs) in order to approximate the pump hydraulic efficiency, hemolysis index (HI), and pressure head. The inverse of the relative pressure head is defined as the first objective and the summation of relative hemolysis index and the inverse of the relative efficiency is assumed as the second objective. Non-dominated Sorting Genetic Algorithm-II (NSGA-II) is used to find the Pareto Front. A set of optimal points is selected. Finally, for the physiological flow conditions, the optimum design that provides 11.9% HI reduction and 7.2% efficiency enhancement is selected.

Shape optimization of a centrifugal blood pump by coupling CFD with metamodel-assisted genetic algorithm.

A centrifugal blood pump is a common type of pump used as a left ventricular assist device in the medical industries. Therefore, the improvement of the device bio-compatibility to reduce the blood damage and to increase the efficiency has become a major challenge. In the current work, a metamodel-assisted genetic algorithm is employed to simultaneously optimize the impeller and volute geometries of a typical centrifugal blood pump. The overall shape of the base design is inspired from HeartMate3 LVAD, and the main dimensions of the base design including inlet and outlet radius, blade angle distribution, volute cross-section area distribution, etc., are designed in our laboratory. Three different scenarios are investigated using three different objective functions, i.e., (1) hydraulic efficiency, (2) pressure head, and (3) hemolysis index (HI). The results showed that the shape optimized by pump efficiency has also nearly the same level of HI as the shape optimized by HI. Hence, to reduce computation time, one can use efficiency instead of HI as an objective function. However, one must check the HI level after such optimization to see whether it is within the acceptable range of HI for such bio application.

Low-inertia centrifugal compressor wheels: Aerodynamic and mechanical design:

A new centrifugal compressor impeller design approach is presented, focusing on electrically driven compressors for gasoline engine and fuel cell applications. The performance and mechanical integrity are evaluated based on numerical simulations. Additionally, the numerical model is applied to several variations of the diffuser and volute geometries, in order to evaluate stage characteristics for diffuser area ratios of 110% and 150%, volute area ratios from 60% to 90%, and diffuser pinch ratios from 60% to 80%. The preliminary performance results show the capability to achieve a flow range comparable to a larger state-of-the-art impeller, with minor penalties regarding stage efficiency and near surge operating stability.

Low-inertia centrifugal compressor wheels: Aerodynamic and mechanical design

A new centrifugal compressor impeller design approach is presented, focusing on electrically driven compressors for gasoline engine and fuel cell applications. The performance and mechanical integrity are evaluated based on numerical simulations. Additionally, the numerical model is applied to several variations of the diffuser and volute geometries, in order to evaluate stage characteristics for diffuser area ratios of 110% and 150%, volute area ratios from 60% to 90%, and diffuser pinch ratios from 60% to 80%. The preliminary performance results show the capability to achieve a flow range comparable to a larger state-of-the-art impeller, with minor penalties regarding stage efficiency and near surge operating stability.

Numerical Analysis and Experimental Verification of an Industrial Cleaner

Cleaner blowers play an important role in the proper functioning of fluffs collection system for industries. In this paper an industrial blower with three different volute geometries is investigated by using Computational Fluid Dynamics (CFD). And then two new volute geometries are modeled and analyzed based on the air flow through the blower. The numerical investigation revealed that the blowers with modified volute geometries have better outlet velocities. For this work, volute is modeled using Solid Works and meshed in ICEM CFD. The post processing is carried out using CFD POST. The results obtained were then validated and compared the experimental values of the different models of the blowers.

Development of new “multivolute casing” geometries for radial force reduction in centrifugal pumps

Large radial force causes several issues in pumps, such as noise, vibration, and extra load on the bearings. To reduce the radial force, the effects of concentric volute and multivolute geometry on the head, efficiency, and radial force of a low speed centrifugal pump at off-design conditions were investigated. Commercial software with the k – ω turbulence model and automatic near wall treatment was employed for the prediction of fluid flow inside the pump. Flow simulations for three casings concentric at 180°, 270°, and 360° from the tongue showed that the 270° concentric volute generates the lowest radial force at throughout the entire range of flow rate. The triple-volute and tetravolute casings are also proposed as new volute geometries. The flow analysis of a double-volute, triple-volute, and tetravolute show that the triple-volute is the most appropriate volute geometry at off-design conditions.

Computational and experimental study of an industrial centrifugal compressor volute

A centrifugal compressor with a vaneless diffuser was studied experimentally and numerically. The main target of the study was to analyze the volute flow. Two different volute geometries was studied. The numerical solution was done by using a steady-state RANS code at both design and off-design conditions. Both calculated and measured pressure and velocity distributions are presented.

Improved Model for the Design and Analysis of Centrifugal Compressor Volutes

This paper describes a new model for the analysis of the flow in volutes of centrifugal compressors. It explicitly takes into account the vortical structure of the flow that has been observed during detailed three-dimensional flow measurements. It makes use of an impeller and diffuser response model to predict the nonuniformity of the volute inlet flow due, to the circumferential variation of the pressure at the volute inlet, and is therefore applicable also at off-design operation of the volute. Predicted total pressure loss and static pressure rise coefficients at design and off-design operation have been compared with experimental data for different volute geometries but only one test case is presented here. Good agreement in terms of losses and pressure rise is observed at most operating points and confirms the validity of the impeller and diffuser response model.