 |
CFD Review |
 |
 |
Site Sponsors |
 |
 |
Tell a Friend |
 |
 |
 |
Help this site to grow by sending a friend an
invitation to visit this site.
|
|
 |
 |
 |
CFD News by Email |
 |
 |
 |
Did you know that you can get today's CFD Review headlines mailed to your inbox?
Just log in and select Email Headlines Each Night on your User Preferences page.
|
|
 |
 |
| |
  |
CFD Assists Nozzle Propeller Design |
|
 |
 |
 |
In our CFD model, we use the powerful rotor/stator capabilities of CFX-TASCflow. The stationary part includes the inflow and outflow regions and the nozzle; the propeller blade and part of the propeller shaft are included in the rotating part. The flow in and around the nozzle varies strongly with Reynolds number. As this increases, the pressure reduction near the leading edge is increased and the separation point near the trailing edge moves backwards. This leads to a change in the operating point of the propeller. To understand these phenomena fully, we undertook an extensive CFD analysis of the flow behavior of the nozzle at different thrust loading conditions and Reynolds number, investigating also different nozzle and propeller geometries.
The results compared well with both published data and LDV measurements behind the nozzle. To analyze the effect of scale on the performance characteristic of our design, we compared the numerical results of three full-scale propellers with the corresponding coefficients of a model propeller. The results showed that with increasing Reynolds number, the thrust coefficient of the nozzle increases (this effect is stronger for low thrust loadings), while the torque and thrust coefficients of the propeller decrease.
The flow velocity through the nozzle at full scale is relatively higher than at model scale. This increases the efficiency of the nozzle at full-scale and reduces the propeller loading (thrust and torque coefficients). Additional reduction of the propeller torque takes place due to the lower friction coefficient on the propeller blades at higher Reynolds numbers. This is one possible explanation for the strong Reynolds-number dependency of the torque coefficient of the ducted propeller in comparison to a free-running one.
The quality of propeller design is directly affected by the ability to accurately predict thrust and torque loading at full scale. The results of the numerical study give the allowed range of extrapolation coefficients that can be used to estimate the full-scale propeller performance based on model-scale data. However, because of the strong dependence of the propeller characteristics on the geometry (thickness, camber, pitch and skew distribution), the results of one numerical study cannot generally be applied to a ducted propeller of another design. Therefore, it is expected that CFD methods will be further involved in the propeller design process to assess the extrapolation of model results to the full scale.
A nozzle propeller in a Z-drive configuration. Propeller courtesy of Schottel Ruder Propeller system (SRP).
Streamlines around a ship hull with a ducted propeller.
Pressure distribution on a nozzle propeller.
Measuring the velocity distribution behind a nozzle propeller in the Potsdam cavitation tunnel.
|
|
 |
 |
[ Post Comment ]
< AVL to Present CFD Lecture at Biomed 2003 | NAFEMS World Congress 2003 > | |
 |
CFD Review Login |
 |
 |
Related Links |
 |
|