Effects of Rotation on Heat Transfer for a Single Row Jet Impingement Array With Crossflow

Abstract

<jats:p>The effects of the Coriolis force are 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 designers’ ability to predict hot spots so coolant 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. A simple case with a single row of constant pitch impinging jets with the crossflow effect is presented to demonstrate the novel liquid crystal technique and document the baseline effects for this type of geometry. The present study examines the differences in heat transfer distributions due to variations in jet Rotation number, Roj, and jet orifice-to-target surface distance (H/dj = 1,2, and 3). Colder air, below room temperature, is passed through a room temperature test section to cause a color change in the liquid crystals. 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, Rej, and average jet Rotation number, Roj. Results show, such as 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 crossflow from upstream spent jets greatly affects impingement heat transfer behavior in the channel. For H/dj = 2 and 3, the effects of the crossflow are not as prevalent as H/dj = 1: however, it still plays a detrimental role. The stationary case shows that heat transfer increases with higher H/dj values, so that H/dj = 3 has the highest results of the three examined. However, during rotation the H/dj = 2 case shows the highest heat transfer values for both the leading and trailing sides. The Coriolis force may have a considerable effect on the developing length of the potential core, affecting the resulting heat transfer on the target surface.</jats:p>

Heat transfer characteristics of high crossflow impingement channels: Effect of number of holes

“…Lamont et al. 10 used a single row of nine impingement holes to study rotation effects. For the stationary case, Nusselt number was increased with increasing channel height due to the less pronounced crossflow effects.…”

“…They noted that impingement flow dominates upstream of the channel beyond a specific point where, as crossflow velocities begin to increase, the deflection of the jets become severe causing a reduction in the heat transfer level. Lamont et al 10 used a single row of nine impingement holes to study rotation effects. For the stationary case, Nusselt number was increased with increasing channel height due to the less pronounced crossflow effects.…”

Effect of Rotation Number on Heat Transfer Characteristics of a Row of Impinging Jets in Confined Channel

“…It is also found that the impinging jet near the outlet of the flow channel (9 th jet to 11 th jet) provides a high local Nusselt number in the impingement region again. This may be due to the crossflow interacted with the jet flow and promoted the turbulent intensity of jet before impinging, which was also explained noticeably for the case of low jet-to-impingement surface distance in previous similar research [16]. The effect of rotations also increases the heat transfer significantly in the trailing surface (TS) when compared with the leading surface (LS) due to the Coriolis and centrifugal acceleration effects.…”

“…They concluded that the rotation could increase the heat transfer rate by up to about 15% when compared to stationary conditions. Recently, the effect of rotation on heat transfer for a single row jet array with crossflow was studied by Lamont et al, [16], who performed at the jet-to-impingement surface distance (L/Dj) of 1, 2, and 3 under the rotational speed of 0 to 275 rpm. They found that the heat transfer rate at L/Dj = 3 gave the highest heat transfer for a stationary case while the rotation cases provided the highest heat transfer at L/Dj = 2.…”

Effect of topology on hybrid-linked jet impingement

“…Investigations combining the effect of target surface conditions and rotation can be found in Elston and Wright [15,16], Hong et al [17][18][19]. and Lamont et al [20][21][22].…”