1965-1967 Research engineer, Dept. internal combustion enginges, Tech. Univ. Vienna, AT
Design of probes for 3D steady-state flow measurement in ICE inflow. Flow measurement and comparison of swirl generators. Supervision of students. Exhaust gas analysis at 4-stroke gasoline engine, studying the influence of fuel injection method and inlet swirl.
1968-1972 Test engineer in thermodynamic lab (BBC Brown Boveri Cie, Baden, CH)
Rig testing of Comprex ® type pressure wave superchargers. Development of 2-wire hot wire anemometry for variable-temperature flow in pressure wave machine. New kind of hill charts for pressure wave superchargers. Development of software for performance prediction of supercharged vehicle engines. Successful bench tests with pressure-wave supercharged versions of truck engines at Saurer (Arbon, CH), Scania (Södertälje, SE) and MAN (Augsburg, DE).
1972-1978 Head of development unit at Comprex ® project(BBC Brown Boveri Cie, Baden, CH)
Development and endurance testing of components for new types of superchargers. Optimization of control geometry. Development studies for runners in vacuum precision casting and high-temperature ceramics.
1978-1984 Research engineer in hydraulic lab (Escher Wyss, Zurich, CH)
First research job: Find out which types of model tests concerning hydraulic puklsations make sense, and how should the results be handled? Survey of then available literature and specific laboratory tests with models of Francis turbines and storage pumps. Also active in troubleshooting for prototype turbines and pumps. I kept these activities until retirement in 2004. Contributing member of the IAHR ‚Work group on the behaviour of hydraulic machinery under oscillatory condition‘ from its start in 1983 until its closure in 2003.
Since 1979 studies on blade-frequent pulsations (troubleshooting for Grimsel II storage pump), starting from Chen’s phase resonance concept (published 1984). Based on model tests using the Karakaya model, I could devise an analytical model for the classical part-load pulsation of the Francis turbines (dissertation 1982). Later I conducted a comparative study of draft tube pressure in many models and found a rule predicting the aeration pressure (published 1986).
1983-1987 Project engineer for hydraulic transients (Sulzer-Escher Wyss, Zurich, CH)
Main activity was the simulation of hydraulic transients, in particular shutdown, in hydro plants with all kinds of hydraulic machines and valves, for the current projects. Such calculations are required for verification of the regulating guarantees (basically pressure and speed rise), and for defining the most suitable servomotor times, quite often also the required flywheel effect of the unit. In addition, this units also determines the necessary actuating forces, and the governor capacity, dimensions and stability. Some projects were fairly complex, or large (Atatürk, TR). In this period I started to develop an efficient, data base oriented software package to handle transient computations for large projects (CITRuS, publication 1993).
Troubleshooting remained an interesting side job throughout this period. Very instructive were the problem solutions in a case of forced vibration at high load (Oymapinar, 1985) and in a case of self-excited vibration at high load (Karakaya, 1986-88), both discussed in Dörfler/Sick/Coutu 2012.
1987-2003 Head of hydraulic transients unit (Sulzer-Escher Wyss – Sulzer Hydro – VATECH)
The CITRuS software for transients and turbine regulation, was finished, ported to PC and made available to several locations of the company. It was (and still is) used for most of the current projects. Interesting tasks resulted from collaboration with the turbine control developers at Zurich. In 1995 I developed fairly simple yet realistic simulation models for all types of hydraulic turbine, which then were implemented in the DTL595 digital governor series of Sulzer Hydro. These algorithms are since then part of the turbine governor software of Sulzer, VATECH and finally Andritz Hydro. Thanks to this feature, control engineers can dry-test the performance of the controlled unit. Later I also provided a model for pump-turbines.
It appeared there is still some potential for interesting problems in hydraulic transients. One example deals with undersized surge tank and how to protect them. In the 1990s I invented the Surge tank Protection Module (SPM, patented) which traces the changing level in the tank and prevents it from draining by inhibiting dangerous manoeuvres of of load. This feature has been implemented in some critical plants, maintaining safety together with as much flexibility of operation as possible.
Another study showed that Thoma’s stability criterion could easily be disposed of; though well-founded (see Dörfler/Lein 2001), this concept did not attract any interest; maybe the worlds of civil engineering and control theory are too much apart.
In this period I also confronted a number of pulsation issues, for instance I solved a case of shaft vibration at a small Francis unit (Toro I, CR), and also a tricky stability problem with synchronizing a 150MW pump-turbine (Bhira, IN).
2004-2013 Part-time employee at VATECH and Andritz Hydro (Zurich, CH)
Since 2004 I mainly worked for research projects. From analysis of model test results from a large number of Francis and pump-turbine models, I could derive statistical laws for the intensity and frequency of the regular part-load pulsation. Starting 2009, I coordinated a numerical investigation of high-load instability. This work produced a significantly improved analytical model, published 2010. It was partly motivated by a (fortunately erroneous) forecast of unstable behaviour for the rehabilitated Guri II turbines. In that context, the question of damping effects is of some importance. Therefore I also analysed an existing quasi-linear model for frequency-dependent pipe friction, using test data from the Bhira penstock.
A research project by Prof. Tsujimoto (Osaka) gave reason to re-visit and adjust the phase resonance concept for blade-frequent pulsations (published 2012-2013).
Later I did some studies concerning the dynamic behaviour of Francis turbines at very low load (published 2012) and during start-up.
Together with two colleagues at Andritz Hydro, I wrote a comprehensive textbook on flow-induced pulsations in hydro units, issued in 2012 at Springer Engineering. In 2013 I held instruction courses about the subject at Andritz Hydro Canada and Brazil.