# R. A. Van den Braembusschevon Karman Institute for Fluid Dynamics · turbomachinery and propulsion

R. A. Van den Braembussche

Research Master in Fluid Dynamics

## About

106

Publications

38,586

Reads

**How we measure 'reads'**

A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more

2,420

Citations

Citations since 2016

Introduction

Centrifugal Compressor Design and Analysis

**Skills and Expertise**

Additional affiliations

October 1973 - October 1980

## Publications

Publications (106)

Design and Analysis of Centrifugal Compressors is a comprehensive overview of the theoretical fluid dynamic models describing the flow in centrifugal compressors and the modern techniques for the design of more efficient centrifugal compressors. The author — a noted expert in the field, with over 40 years of experience — evaluates relevant numerica...

This chapter provides a short overview of the different non‐axisymmetric inlet and outlet geometries for radial impellers. It describes the advantages and disadvantages of the different types, and explains the relation between the geometry and the flow in terms of performance and circumferential pressure distortion. Inlet and outlet volutes are dis...

It has been observed by Kenny that a supersonic flow at the vaned diffuser inlet has no detrimental effect on performance. In addition to a change in the impeller inlet Mach number, variable inlet guide vanes (IGVs) can also be used to adjust the mass flow in order to increase the operating range. The inducer has a large impact on the impeller perf...

This chapter concentrates on the unsteady impeller response to the downstream pressure distortion, imposed by volutes operating at off‐design. After a short overview of some experimental data, it discusses the flow mechanisms governing unsteady incompressible and compressible flow. The chapter describes the 1D and full 3D unsteady flow calculation...

This chapter provides insight into the flow structure based on theoretical considerations and on the results of numerical experiments. It describes and quantifies the various forces and losses that govern the 3D structure of the flow as a function of the impeller geometry and operating conditions. The chapter describes the interaction between the i...

The performance of a diffuser is normally not characterized by the efficiency but by the pressure coefficient relating the amount of kinetic energy that has been transformed into static pressure to the inlet kinetic energy. Vaneless diffusers are better suited for off‐design operation because they allow a large variation of absolute inlet flow angl...

This chapter presents a more detailed definition of surge and stall, based on a theoretical description and the main characteristics. It attempts to classify the different phenomena in a logical way. Rotating stall can be generated by the destabilization of the impeller or diffuser flow, or by an unsteady interaction between impeller and diffuser....

This chapter describes inverse design methods defining the geometry corresponding to a prescribed "optimal" pressure or velocity distribution. The main advantage of the inverse design methods is the ability to design in detail very specific blade geometries, such as controlled diffusion blades and shock‐free transonic blades. Two types of inverse d...

This chapter discusses some specific actions and geometrical modifications that aim to extend the operating range of centrifugal compressors. Active surge control prevents an initial flow perturbation being amplified to large amplitude instabilities. The increase in the operating range by active control is achieved by modifying the system dynamics,...

In this study a centrifugal compressor impeller for an automotive turbocharger was designed by means of an aerodynamic design optimization system composed of an artificial neural network (ANN) and a genetic algorithm (GA). This resulted in two newly designed centrifugal compressor impellers which were further studied both numerically and experiment...

A similitude method to model the tip clearance flow in a high-speed compressor with a low-speed model is presented in this paper. The first step of this method is the derivation of similarity criteria for tip clearance flow, on the basis of an inviscid model of tip clearance flow. The aerodynamic parameters needed for the model design are then obta...

This paper first describes the requirements that a modern design system should meet, followed by a comparison between design systems based on inverse design or optimization techniques. The second part of the paper presents the way these challenges are realized in an optimization method combining an Evolutionary theory and a Metamodel. Extensions to...

A transonic centrifugal compressor for turbocharger applications has been redesigned by means of a multidisciplinary multipoint optimization system composed of: a 3D Navier-Stokes solver, a Finite Element stress Analyzer, a Genetic Algorithm and an Artificial Neural Network. The latter makes use of a database, containing the geometry and correspond...

Concurrent aerodynamic, aeroacoustic and aeroelastic optimization of transonic propeller blades is performed with a Multi-Objective Differential Evolution technique. The optimization process relies on a metamodel to deliver performance estimates as well as on recurrent Computational Fluid Dynamics, Computational Hybrid Aeroacoustics and Computation...

In centrifugal compressors, variable inlet guide vanes (IGVs) are used to control the mass flow rate with negligible change in pressure ratio and shaft speed. The efficient operation of IGVs is limited to the range of aerodynamic stability of their vane profiles. Thin symmetric profiles, which are usually used, tend to exhibit flow separation alrea...

This paper presents a 3-D optimization of a moderately loaded transonic compressor rotor by means of a multi-objective optimization system. The latter makes use of a Differential Evolutionary Algorithm in combination with an Artificial Neural Network and a 3D Navier-Stokes solver. Operating it on a cluster of 30 processors enabled the optimization...

This paper presents an optimization method applied to the design of a radial compressor. The optimization method is based on a metamodel assisted differential evolution algorithm to find a compromise between the conflicting demands of high efficiency and low centrifugal stresses in the blades. A concurrent approach is presented where both disciplin...

Two dimensional time accurate PIV measurements of the flow between pressure and suction side at different spanwise positions
of a rotating channel are presented. The Reynolds and Rotation numbers are representative for the flow in radial impellers
of micro gas turbines. Superposition of the 2D results at the different spanwise positions provides a...

A multidisciplinary optimization system and its application to the design of a small radial compressor impeller are presented. The method uses a genetic algorithm and artificial neural network to find a compromise between the conflicting demands of high efficiency and low centrifugal stresses in the blades. Simultaneous analyses of the aero perform...

This paper reports on an experimental and numerical study at low Reynolds number in order to evaluate the influence of the
Coriolis forces on the flow in radial rotating channels. Operating conditions correspond to the flow in radial impellers for
micro gasturbine applications. A comparison of detailed flow measurements with CFD results indicates t...

This first paper describes the conjugate heat transfer (CHT) method and its application to the performance and lifetime prediction of a high pressure turbine blade operating at a very high inlet temperature. It is the analysis tool for the aerothermal optimization described in a second paper. The CHT method uses three separate solvers: a Navier-Sto...

This second paper presents the aerothermal optimization of the first stage rotor blade of an axial high pressure (HP) turbine by means of the conjugate heat transfer (CHT) method and lifetime model described in Paper I. The optimization system defines the position and diameter of the cooling channels leading to the maximum lifetime of the blade whi...

The present paper addresses a simple truncation technique applied to cope with the sonic singularity so that noise from propellers can be computed in the subsonic as well as transonic and low supersonic domain at low numerical cost. Based on Farassat's 1A formulation of the Ffowcs Williams-Hawkings (FW-H) acoustic analogy, the present method comput...

Two dimensional time accurate PIV measurements of the flow between pressure and suction side at different spanwise positions of a rotating channel are presented. The Reynolds and Rotation numbers are representative for the flow in radial impellers of micro gas turbines and the cooling channels of large HP gas turbines. Superposition of the 2D resul...

This paper describes the aerodynamic design and explores the performance limits of a 600 MWt multistage helium turbine for a high temperature nuclear reactor closed cycle gas turbine. The design aims for maximum performance while limiting the number of stages for reasons of rotor dynamics and weight.A first part discusses the arguments that allow a...

Turbomachinery components used in rocket engines are submitted to extreme aero-thermal loads. To ensure the safe operation of the turbine rotor, the sources of aerodynamic unsteadiness must be identified and quantified. The present investigation addresses the aerodynamic flow field in the turbine manifold and nozzle guide vanes of the Vulcain 2 LOX...

In this paper the authors show an original application to time-resolved PIV of an existing method for confidence level and
error determination, called dependent bootstrapping. Due to the high sampling frequencies the measured velocity samples are
no longer uncorrelated making classical statistical procedures not applicable. Examples show that the v...

A new facility to measure the time evolution of 2D velocity fields in a rotating channel is presented, and the accuracy is
discussed in detail. Measurements are made by means of a time-resolved PIV system composed of a continuous laser diode, coupled
by a fiber optics cable to a laser plane optical module, and a CMOS high-speed camera. Both the PIV...

Internal volutes have a constant outer radius, slightly larger than the diffuser exit radius, and the circumferential increase of the cross section is accommodated by a decrease of the inner radius. They allow the design of compact radial compressors and hence are very attractive for turbochargers and high-pressure pipeline compressors where small...

This first paper describes the Conjugate Heat Transfer (CHT) method and its application to the performance and lifetime prediction of a high pressure turbine blade operating at a very high inlet temperature. It is the analysis tool for the aerothermal optimization described in a second paper. The CHT method uses three separate solvers: a Navier-Sto...

This second paper presents the aerothermal optimization of the first stage rotor blade of an axial HP turbine by means of the conjugate heat transfer method (CHT) and lifetime model described in paper 1. The optimization system defines the position and diameter of the cooling channels leading to the maximum lifetime of the blade while limiting the...

The multilevel-multidisciplinary-multipoint optimization system developed at the von Kármán Institute and its applications to turboma-chinery design is presented. To speed up the convergence to the optimum geometry, the method combines an Artificial Neural Network, a Design Of Experiment technique and a Genetic Algorithm. The different components a...

The current paper presents a numerical investigation of the conjugate heat transfer (CHT) in an axial helium turbine. The objective is the prediction of the cooling needed to keep the blade temperature below the allowable material limits. The cooling is applied at the hub by means of internal cooling channels.
A CHT solver has been developed for th...

This paper describes the development of a microgasturbine with a rotor diameter of 20 mm. The target electrical power output lies around 1 kW. The total system fits in a cylinder with a diameter of 95 mm and a length of 120 mm. The system contains the same components as a large gasturbine generator: compressor, recuperator, combustion chamber, turb...

The impact of Coriolis forces on low Reynolds number decelerating flows is studied by means of time resolved Particle Image Velocimetry in a 6° diverging channel. Measurements are made with a high speed camera and a continuous light source rotating at the same speed as the rotating channel. This allows a direct and accurate recording of the time va...

These lecture notes provide an overview of the different inlet and outlet volutes for radial impellers. It describes the advantages and disadvantages of the different geometries, the relation between flow and geometry, the impact on the downstream or upstream impeller, the loss mechanisms and some loss prediction models. The main purpose is to prov...

This paper presents a numerical investigation of the heat transfer inside a micro gasturbine and its impact on the performance. The high temperature difference between turbine and compressor in combination with the small dimensions results in a high heat transfer causing a drop in efficiency of both components. Present study aims to quantify this h...

Battery systems have a much lower energy density than fuels. The use of fuel based micro power generation units instead of batteries can therefore become interesting in certain applications. This paper describes the problems that occur when designing such a power generation unit. It is shown that operational conditions and geometrical restrictions...

Introduction The current trend to-wards miniaturiza-tion, portability and, more generally, ubiq-uitous intelligence has led to the develop-ment of a wide range of new products such as laptops, cellular phones, PDAs, etc. However, the power requirements of such systems have received much less attention: typically, traditional battery-operated elec-t...

The design and optimization of a multistage radial compressor vaneless diffuser, cross-over and return channel is presented. An analytical design procedure for 3D blades with prescribed load distribution is first described and illustrated by the design of a 3D return channel vane with leading edge upstream of the cross-over. The analysis by means o...

In transonic turbine stages, the exit static pressure field of the vane is highly non-uniform in the pitchwise direction. The rotor traverses periodically this non-uniform field and large static pressure fluctuations are observed around the rotor section. As a consequence the rotor blade is submitted to significant variations of its aerodynamic for...

The goals in performance that are presently put forward for advanced turbomachines can only be achieved by a careful consideration of the three-dimensional (3D) geometric effects and secondary flows. The two-dimensional (2D) cascade concept for blade design is nowadays useful only as a first guess of the optimum geometry.

The design and optimisation of a vaneless diffuser, cross-over and return channel of a multistage radial compressor is presented. Special attention is given to the extension of the vanes upstream of the cross-over.
These unconventional vanes are designed by a new 3D procedure that is based on the equations for irrotational flow and accounts for mer...

This paper presents a novel iterative viscous inverse method for turbomachinery blading design. 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 ingredien...

The use of a three-dimensional inverse method for the design of inlet guide vanes, a centrifugal impeller and return channel is demonstrated. The geometry of the different components are iteratively defined until a prescribed velocity distribution is obtained.
The procedure and design criteria for each component are described and the final result i...

A numerical procedure for the design of a centrifugal compressor impeller with prescribed isentropic Mach number distribution along the blade suction and pressure side is described. Both the blade shape and the endwalls are defined at the same time. This method is a combination of a 3D and a quasi-3D flow analysis programs with a quasi-3D geometry...

This paper presents the experimental and numerical investigation of an outward volute of rectangular cross section. The investigation is carried out at the level of
- stage performance,
- volute performance and
- detailed flow field study at selected peripheral positions for various operating points.
The objective of the investigation was to gain f...

This paper describes two modern methods for turbomachinery blade design and illustrates them with examples. The first one uses an Artificial Neural Network to extract knowledge from a database containing the results of previous designs and Simulated Annealing to generate new blades. The method is well suited to account for mechanical and manufactur...

A numerical procedure to predict the impeller/volute interaction in a single-stage centrifugal compressor is presented. The method couples a three-dimensional unsteady flow calculation in the impeller with a three-dimensional time-averaged flow calculation in the volute through an iterative updating of the boundary conditions on the interface of bo...

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 now that has been observed during detailed 3D flow measurements. It makes use of an impeller and diffuser response model to predict the non-uniformity of the volute inlet flow due, to th...

A new three-dimensional inverse method for the design of compressor and turbine blades is presented. The method solves the time dependent Euler equations in a numerical domain of which some boundaries (the blade walls) are iteratively modified until a prescribed pressure distribution is reached.Each iteration of the procedure starts with a blade mo...

This paper describes a knowledge-based method for the automatic design of more efficient turbine blades. An Artificial Neural Network (ANN) is used to construct an approximate model (response surface) using a database containing Navier Stokes solutions for all previous designs. This approximate model is used for the optimization, by means of Simula...

We present iterative inverse design methods for compressor and turbine blades, with prescribed Mach number or pressure distribution. It is explained how the permeable wall concept can be used to define the blade modifications required to obtain the target performance with a small number of iterations. It is also shown how the method can be combined...

The use of a three-dimensional Euler inverse method for the design of a centrifugal impeller is demonstrated.
Both the blade shape and the endwalls are iteratively designed. The meridional contour is modified in order to control the mean velocity level in the blade channel, while the blade shape is designed to achieve a prescribed loading distribut...

This paper deals with the modeling of the flow in the leakage cavity between shroud and stator of a radial pump and the design of optimized swirl brakes at the inlet of the seal. As pressure losses were of no importance in this application, the only criterion for optimization was to minimize the swirl at the seal inlet in order to enhance the rotor...

This paper deals with the design of an optimised compressor blade and the experimental verification of its performance at design and off-design operation.
Starting from an existing controlled-diffusion blade, a new two-dimensional blade section has been designed by means of an inverse method, maintaining the same flow turning. Optimisation is made...

An iterative procedure for 3D blade design is presented. The three-dimensional blade shape is modified using a physical algorithm, based on the transpiration model. The transpiration flux is computed by means of a modified Euler solver, in which the target pressure distribution is imposed along the blade surfaces. Only a small number of modificatio...

A lumped parameter model to predict the high frequency pressure oscillations observed in a water brake dynamometer is presented. It explains how the measured low frequency variations of the torque are a consequence of the variation in amplitude of the high frequency flow oscillations. Based on this model, geometrical modifications were defined, aim...

The flow in a centrifugal compressor stage is dominated by the geometry of the impeller, the diffuser and the exit collecting chamber. Asymmetries of the flow field in the annular space behind the impeller may create a circumferential pressure distortion, influencing the energy transfer by the impeller in a negative way, creating variable force on...

A two-dimensional viscous inverse method for the design of compressor and turbine blades is presented. It iteratively modifies an initial geometry until a prescribed pressure distribution is reached on the blade surface.
The method solves the time-dependent Navier—Stokes equations in a numerical domain of which some boundaries (the blade walls) mov...

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 3D Euler solver with non-reflecting upstream and downstream boundary conditions and phase-lagged periodicity conditions is used for this purpose.
The mechanisms gove...

The aim of the present paper is the investigation of the influence of non-reflecting boundary conditions on the calculation of the three-dimensional inviscid steady rotational flow inside a high pressure ratio centrifugal impeller.
The space discretization of the Euler equations was done using the finite volume technique and the multistep Runge-Kut...

In this paper we present a finite-element-based methode for the calculation of the unsteady potential flow in rotor/stator configurations. A numerical algorithm was developed to calculate the two-dimensional flow through a centrifugal volute pump, taking into account the width variation of the volute in the axial direction and the vortex wakes down...

The improvement of centrifugal compressor performance and the control of the radial forces acting on the impeller due to the circumferential variation of the static pressure caused by the volute require a good understanding of the flow mechanisms and an accurate prediction of the flow pattern inside the volute. A three-dimensional volute calculatio...

Detailed measurements of the swirling flow in a centrifugal compressor
volute with elliptical cross section are presented. They show important
variations of the swirl- and through-flow velocity, total and static
pressure distribution at the different volute cross sections and at the
diffuser exit. The basic mechanisms defining the complex 3D flow
s...

The improvement of centrifugal compressor performance and the control of the radial forces acting on the impeller due to the circumferential variation of the static pressure caused by the volute require a good understanding of the flow mechanisms and an accurate prediction of the flow pattern inside the volute. A 3D volute calculation method has be...

An iterative procedure for blade design, using a Time Marching procedure to solve the unsteady Euler equations in the blade-to-blade plane is presented. A flow solver, which performs the analysis of the flow field for a given geometry, is transformed into a design method. This is done by replacing the classical slip condition (no normal velocity co...

This paper describes the design of realistic blade shapes using an inverse method. Special attention is given to the geometrical and mechanical constraints imposed upon the blade.
Examples presented in this paper illustrate how a better understanding of the theoretical relations between imposed velocity and resulting geometry can help satisfy the g...

The detailed three-dimensional velocity distributions, corresponding to design and off-design operation, were measured in two different circumferential cross sections of a volute by means of LDV. It is shown that the swirl has a forced vortex type velocity distribution and that the location of the swirl center is changing with mass flow. The throug...

This paper describes a method for the design of airfoils with prescribed
Mach number or static pressure distribution along both the suction and
pressure sides. The method consists of an iterative procedure, in which
the final geometry is obtained through successive modifications of an
existing shape. Each modification is computed by solving the Eul...

A detailed study of the swirling flow in a rectangular volute of a centrifugal compressor is presented. The 3D flow field has been measured by means of a five hole probe at six different cross sections for three different operating points of the compressor.
For high mass flow, the large radial velocity component at the diffuser exit creates a stron...

Measurements of the three-dimensional flow in a simplified model of a centrifugal compressor volute at design and off-design operation are presented. A nearly constant swirl velocity is observed near the walls and a forced vortex type of flow is observed in the center. This velocity distribution is almost identical at all cross sections and all ope...

This work presents the application of particle image displacement velocimetry to the measurement of fluid velocities in a centrifugal pump diffuser. Measurements are taken at different operating points and allow to define the variation of radial and tangential velocity components along a pitch. They are further processed to determine the relative v...

The transonic flow in an existing radial vaned diffuser has been analysed with a time dependent finite area calculation method. The calculated Mach number distribution indicates a strong bow shock upstream of the throat. Based on this experience, new diffusers have been designed in order to optimize the Mach number distribution in the semi-vaneless...

Detailed velocity measurements, using Laser Doppler Anemometry (LDA) and static pressure measurements in the vaneless diffuser of a centrifugal compressor, are presented. They show the relation between the circumferential variation of the pressure and the local flow in the diffuser and at the impeller exit. Theoretical calculations using an impelle...