The effects of the Coriolis force and centrifugal buoyancy is investigated in rotating internal serpentine coolant channels in turbine blades. For complex flow in rotating channels, detailed measurements of the heat transfer over the channel surface will greatly enhance the blade designer’s ability to predict hot spots so coolant air may be distributed more effectively. The present study uses a novel transient liquid crystal technique to measure heat transfer in a rotating, radially outward channel with impingement jets. This is the beginning of a comprehensive study on rotational effects on jet impingement. A simple case with a single row of constant pitch impinging jets with crossflow effect is presented to demonstrate the novel liquid crystal technique and document the baseline effects for this type of geoemtry. The present study examines the differences in heat transfer distributions due to variations in jet Rotation number and jet orifice-to-target surface distance. Colder air below room temperature is passed through a room temperature test section to simulate the centrifugal buoyancy effect seen in a real engine environment. This ensures that buoyancy is acting in a similar direction as in actual turbine blades where walls are hotter than the coolant fluid. Three parameters were controlled in the testing: jet coolant-to-wall temperature ratio, average jet Reynolds number, and average jet Rotation number. Results show, like serpentine channels, the trailing side experiences an increase in heat transfer and the leading side experiences a decrease for all jet channel height to jet diameter ratios (H/dj). At a jet channel height to jet diameter ratio of 1, the cross-flow from upstream spent jets greatly affects impingement heat transfer behavior in the channel.
The effects of the Coriolis force and centrifugal buoyancy are well known in rotating internal serpentine coolant channels in turbine blades. As channel flow in rotation is highly complex, detailed knowledge of the heat transfer over a surface will greatly enhance the blade designer’s ability to predict hot spots so coolant may be distributed effectively. The present study uses a novel transient liquid crystal technique to measure heat transfer on a rotating two-pass channel surface with chilled inlet air. The present study examines the differences in heat transfer distributions of three channel types in rotation: smooth wall, 90° ribs, and W-shaped ribs. The two channels in the test section model radially inward and outward flow. To account for centrifugal buoyancy, cold air is passed through a room temperature test section. This ensures that buoyancy is acting in a similar direction to real turbine blades. Three parameters were controlled in the testing: inlet coolant-to-wall density ratio, channel Reynolds number, and Rotation number. Results were compared to previous studies with similar test conditions. The present study shows that the W-shaped ribs enhance heat transfer in all cases (stationary and rotating) approximately 2–3 times better than the 90° ribs. The W-shaped ribbed channel is least affected by rotation due to the complex nature of the flow generated by the geometry.
Coolant flow in rotating internal serpentine channels is highly complex due to the effects of the Coriolis force and centrifugal buoyancy. Detailed knowledge of the heat transfer over a surface will greatly enhance the blade designers’ ability to predict hot spots so coolant may be distributed effectively. The present study uses a novel transient liquid crystal technique to measure heat transfer on a rotating two-pass channel surface with chilled inlet air. The present study examines the differences in heat transfer distributions on channel surfaces with smooth walls, 90 deg rib and W-shaped rib turbulated walls. The test section is made up of two passes to model radially inward and outward flows. To account for centrifugal buoyancy, cold air is passed through a room temperature test section. This ensures that buoyancy is acting in a similar direction to real turbine blades. The inlet coolant-to-wall density ratio is fixed at 0.08, Re = 16,000, and Ro = 0.08. The present study shows that the W-shaped ribs enhance heat transfer in all cases (stationary and rotating) approximately 1.75 times more than the 90 deg ribs. The W-shaped rib channel is least affected by rotation, which may be due to the complex nature of the secondary flow generated by the geometry. A higher pressure drop is associated with the W-shaped ribs than the 90 deg ribs, however, the overall thermal-hydraulic performance of the W-shaped ribs still exceeds that set by the 90 deg ribs.
The effects of CorioHs force and centrifugal buoyancy have a significant impact on heat transfer behavior inside rotating internal serpentine coolant channels for turbine blades. Due to the complexity of added rotation inside such channels, detailed knowledge of the heat transfer will greatly enhance the blade designer's abiiity to predict hot spots so coolant may be distributed more effectively. The effects of high rotation numbers are investigated on the heat transfer distributions for different rib types in near entrance and entrance region of the channels. It is important to determine the actuai enhancement derived from turbulating channel entrances where heat transfer is already high due to entrance effects and boundary layer growth. A transient liquid crystal technique is used to measure detailed heat transfer coefficients (htc)for a rotating, short length, radially outward coolant channel with rib turbuiators. Different rib types such as 90 deg, W, and M-shaped ribs are used to roughen the walls to enhance heat transfer. The channel Reynolds number is held constant at 12,000 while the rotation number is increased up to 0.5. Results show that in the near entrance region, the high performance W and M-shaped ribs are just as effective as the simple 90 deg ribs in enhancing heat transfer. The entrance effect in the developing region causes significantiy high baseline heat transfer coefficients thus reducing the effective of the ribs to further enhance heat transfer. Rotation causes increase in heat transfer on the trailing side, while the leading side remains relatively constant limiting the decrement in leading side heat transfer. For all rotational cases, the W and M-shaped ribs show significant effect of rotation with large differences between leading and trailing side heat transfer.
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