Ralf Jakoby

Correlations of the Convection Heat Transfer in Annular Channels With Rotating Inner Cylinder

In the internal air system of gas turbine engines or generators, a large variety of different types of annular channels with rotating cylinders are found. Even though the geometry is very simple, the flow field in such channels can be completely three-dimensional and also unsteady. From the literature it is well-known that the basic two-dimensional flow field breaks up into a pattern of counter-rotating vortices as soon as the critical speed of the inner cylinder is exceeded. The presence of a superimposed axial flow leads to a helical shape of the vortex pairs that are moving through the channel. For the designer of cooling air systems there are several open questions. Does the formation of a Taylor-vortex flow field significantly affect the convective heat transfer behavior of the channel flow? Is there a stability problem even for high axial Reynolds-numbers and where is the location of the stability boundary? After all, the general influence of rotation on the heat transfer characteristics has to be known. By the results of flow field and heat transfer measurements, the impact of rotation and the additional influence of Taylor-vortex formation on the heat transfer characteristics in annular channels with axial throughflow will be discussed. The flow field was investigated by time-dependant LDA-measurements, which revealed detailed information about the flow conditions. By a spectral analysis of the measured data, the different flow regimes could be identified. Based on these results, the heat transfer from the hot gas to the rotating inner shaft was determined with a steady-state method. Thus, the influence of the different physical phenomena such as rotation with and without Taylor-vortex formation or the flow development could be separated and quantified. Finally, correlations of the measured results were derived for technical applications.

Experimental and Numerical Study of Orifice Discharge Coefficients in High-Speed Rotating Disks

Experimental and numerical results of the flow through orifices in rotating disks are presented, with emphasis on basic physical phenomena. It is shown that rotational effects strongly influence the massflow discharged, a phenomenon that cannot be modeled by a stationary setup. The study includes the determination of discharge coefficients under variation of the length-to-diameter ratio, pressure ratio, and rotational speed. The pressure ratio covers low as well as critical values, the maximum rotational speed is 10,000 rpm, which is equivalent to a tangential velocity of 110 m/s. In order to understand the flow structure, local flow velocities were measured by means ofa two-dimensional Laser-Doppler Velocimeter. Phase-resolved measurements have been carried out in front of and behind the orifices. A three-dimensional Finite-Volume Code with body-fitted coordinates in a rotating frame of reference is employed for the numerical analysis and the verification of its possibilities and limitations. The results reveal a very complex flow field, which is dominated by high velocity gradients in close vicinity to the orifices. The comparison of the computational solutions with the experimental data shows good agreement. Based on the measurements in combination with the numerical solution, a detailed insight into the physical properties of the flow is achieved.

Characteristics of discharge coefficient in a rotating disk system

The discharge coefficient of a long orifice in a rotating system is measured to examine the rotational effect on discharge behavior. The rotating system is comprised of a rotating disk and two stators on both sides of the rotating disk. Test rig is constructed to simulate the real turbine operating conditions. Pressure ratios between upstream and downstream cavities of the orifice range from 1.05 to 1.8, and rotational speed of the rotor disk is varied up to 10,000 rpm. The orifice hole bored through the rotor disk has length-to-diameter ratio of 10. For a better interpretation of discharge behavior, three-dimensional velocity field in the downstream and upstream cavities of the rotor is measured using a Laser Doppler Velocimetry. A new definition of the rotational discharge coefficient is introduced to consider the momentum transfer from the rotor to the orifice flow. Additional loss in the discharge coefficient due to pressure loss in the orifice hole at the inlet and exit regions is quantitatively presented in terms of the Rotation number and the compressibility factor. The effect of corner radiusing at the orifice inlet is also investigated at various rotational conditions.

Characteristics of Discharge Coefficient in a Rotating Disk System

The discharge coefficient of a long orifice in a rotating system is measured to examine the rotational effect on discharge behavior. The rotating system is comprised of a rotating disk and two stators on both sides of the rotating disk. Test rig is constructed to simulate the real turbine operating conditions. Pressure ratios between upstream and downstream cavities of the orifice range from 1.05 to 1.8, and rotational speed of the rotor disk is varied up to 10,000 rpm. The orifice hole bored through the rotor disk has length-to-diameter ratio of 10. For a better interpretation of discharge behavior, three-dimensional velocity field in the downstream and upstream cavities of the rotor is measured using a Laser Doppler Velocimetry. A new definition of the rotational discharge coefficient is introduced to consider the momentum transfer from the rotor to the orifice flow. Additional loss in the discharge coefficient due to pressure loss in the orifice hole at the inlet and exit regions is quantitatively presented in terms of the Rotation number and the compressibility factor. The effect of comer radiusing at the orifice inlet is also investigated at various rotational conditions.Copyright

Correlations of the Convective Heat Transfer in Annular Channels With Rotating Inner Cylinder

In the internal air system of gas turbine engines or generators, a large variety of different types of annular channels with rotating cylinders are found. Even though the geometry is very simple, the flow field in such channels can be completely three-dimensional and also unsteady. From the literature it is well-known, that the basic two-dimensional flow field breaks up into a pattern of counter-rotating vortices, as soon as the critical speed of the inner cylinder is exceeded. The presence of a superimposed axial flow leads to a helical shape of the vortex pairs, which are moving through the channel.For the designer of cooling air systems there are several open questions. Does the formation of a Taylor-vortex flow field significantly affect the convective heat transfer behaviour of the channel flow? Is there a stability problem even for high axial Reynolds-numbers and where is the location of the stability boundary? After all, the general influence of rotation on the heat transfer characteristics has to be known.By the results of flow field and heat transfer measurements, the impact of rotation and the additional influence of Taylor-vortex formation on the heat transfer characteristics in annular channels with axial throughflow will be discussed. The flow field was investigated by time-dependant LDA-measurements, which revealed detailed information about the flow conditions. By a spectral analysis of the measured data, the different flow regimes could be identified. Based on these results, the heat transfer from the hot gas to the rotating inner shaft was determined with a steady-state method. Thus, the influence of the different physical phenomena such as rotation with and without Taylor-vortex formation or the flow development could be separated and quantified. Finally, correlations of the measured results were derived for technical applications.Copyright

Flow Characteristics of a Highly Rotating Turbine Cavity System With Discharge Hole

An experimental investigation is performed to analyze the flow characteristics of a turbine cavity system containing discharge holes installed in a rotating disk. The turbine cavity system is composed of a rotating disk and two stationary disks on both sides of the rotating disk. The air flow is induced into the upstream cavity, and then discharged into the downstream cavity through 8 discharge holes in the rotating disk. The flow field in each cavity at high-speed rotation of the rotor was measured by a three-dimensional LDV system. The measured flow field is analyzed to understand the flow structures, and further provide information for studying the heat transfer behaviors of the turbine disk system. The overall flow field in the upstream cavity shows a negligible axial velocity with a relatively small rotational velocity, less than 10% of the rotor speed. The downstream cavity flow has a high rotational velocity close to the rotational speed of the discharged jets, due to the direct circumferential momentum transfer from the discharged jets. The interaction between the discharged jet and the downstream stator disk induces an asymmetric development of the spreading wall jet, which results in a relative circumferential motion to the revolving discharged jet. The whole flow field in the downstream cavity is divided into several flow regions according to their features.Copyright