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Velocity Measurements In an Automotive TorqueConverter—Part II: Average Turbine and StatorMeasurementsRonald D. Flack a & Leonard D. Whitehead ba University of Virginia, Department of Mechanical, Aerospace and Nuclear Engineering ,Charlottesville, Virginia, 22903-2442b Blue Ridge Numerics, Inc. , Charlottesville, Virginia, 22903Published online: 25 Mar 2008.

To cite this article: Ronald D. Flack & Leonard D. Whitehead (1999) Velocity Measurements In an AutomotiveTorque Converter—Part II: Average Turbine and Stator Measurements, Tribology Transactions, 42:4, 697-706, DOI:10.1080/10402009908982272

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Velocity Measurements In an Automotive Torque Converter-Part II:

Average Turbine and Stator ~easurements~

RONALD D. FLACK University of Virginia

Department of Mechanical, Aerospace and Nuclear Engineering Charlottesville, Virginia 22903-2442

and LEONARD D. WHITEHEAD

Blue Ridge Numerics, Inc. Charlottesville, Virginia 22903

Laser velocimetry was used to measure the flow field in the

turbine and stator of an automotive torque converter. The data

complements that of data in a pump at the same operating condi-

tions. Average velocities are presented and analyzed in this paper

for three turbine/pump speed ratios (0.065, 0.600, and 0.800).

Data presented in this paper embody the most detailed velocity

measurements in torque converters available. At all speed ratios

and in all turbine measurement planes the highest through flow

velocities generally occurred at the pressure side of the channel.

At the turbine inlet a velocity deficit near the core was observed.

This is due to the velocity deficit at the pump exit that transmits to

the turbine inlet. At the lowest speed ratiopow entered the turbine

with significant "pre-swirl" causing the flow to separate on the

suction surface between the inlet and the mid-plane, resulting in a

separation region in the core-suction quadrant. Strong circulato-

ry secondary flows were not observed in the turbine planes as they

were in the pump planes. The measured vorticity was highest at

the inlet plane. The torque distribution was found between the

inlet and mid-planes and mid- and exit planes of the turbine. The

chord wise distribution was uneven and most of the torque was

derived from the fluid between the inlet and mid-plane. The stator

flow field is relatively uniform at the inlet at the highest speed

ratio but much less so at the lower speed ratios. Some separation

is seen at the lowest speed ratio at the inlet. At the highest speed

ratio flow enters the stator with little incidence to the blades. At

lower speed ratios significant incidence was measured resulting

Presented at the 54th Annual Meeting Las Vegas, Nevada

May 23-27,1999 Flnal manuscrlpt approved January 6,1999

in separation on the suction surface. For the highest two speed

ratios a significant separation region was observed at the exit

plane in the suction/shell quadrant of the stator: The torque distri-

bution was found between the stator inlet and mid-planes and

mid- and exit planes. The total torque delivered to the working

fluid at the 0.065 speed ratio is significant, indicating the presence

of torque multiplication. At the 0.800 speed ratio the torque dis-

tribution between all planes is minimal, indicating minimal torque

multiplication. The chord-wise torque distribution is relatively

even.

The typical torque converter consists of a pump, a turbine, and a stator, and employs oil as the working fluid. Rotational energy from the automobile engine is introduced into the fluid by the pump and extracted by the turbine. For the pump and turbine the flow is turned in the transverse direction, usually in a short dis- tance; namely, flow enters these components in the axial direction, rapidly is turned to the radial direction, and rapidly turned into the reverse axial direction. Thus, the torque converter pump and tur- bine are of the very complex mixed-flow variety of hydraulic tur- bomachines. The stator is placed between the turbine exit and pump inlet and it is essentially an axial flow turbomachine com- ponent. It's function is to ideally create a zero pump inlet blade incidence angle at some design conditions.

The design of a torque converter is very complex due to a num- ber of conditions. First, the turbomachine should operate effi- ciently at both on- and off-design conditions. However, the flow field changes drastically over the typical operating range; namely, incidence angles to all of the components change from large pos- itive to large negative values over the operating range. Second, the flow is turned in the passages in two directions. As in any turbo- machine, blade slip becomes a problem at off-design conditions and the flow does not follow the blades. The problem is further

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Inlet Plane \

TURBlHe

- T.C. HOUBlNO

Plow Rom Pump -

Flow Into Stator -

Flg. 1-Torque converter cross sectional view showlng containment box and dlmenslons.

complicated by the fact that the pump and turbine are mixed-flow turboniachines.

Review Of Previous Torque Converter Studies

In Part I of this paper the literature was reviewed in detail. It will not be repeated in this part.

Motivations and Objectives of the Current Research

Thcoretical analysis of the torque converter has not developed to a level permitting design solely from computational results. Threc-dimensional experimental flow data, including velocity dis- tribution, pressures, and turbulence intensities, are required to ver- ify computational results. The current understanding of the inter- nal flow field of the torque converter is inadequate.

Three primary incentives motivate research in torque convert- cr llow fields. First, the current hydrodynamic design tools need to be upgraded in order to advance torque converter technology signiiicantly. Thus, benchmark velocity data is needed to verify co~nputational methods. Second, the torque converter can be a rel- ativcly inefficient machine. Improvement in torque converter effi- ciency can be obtained by optimizing the internal flow paths through each component. However, before flow passages are modified an understanding of the fundamental flow behavior is necded so that problem regions can be identified. Third, the pump is the driving mechanism and the turbine is the energy absorber of

Fig. 2-Turblne passage geometry.

Plane

the torque converter. These components are extremely complex mixed-flow turbomachines; namely, the flow is both axial and radial in most regions of both impellers. A basic understanding of mixed-flow behavior is essential for the design process, not only for torque converter pumps and turbines but for other mixed-flow turbomachines as well.

In this paper, a laser velocimeter was used to measure veloci- ty components in the turbine and stator of an automobile torque converter constructed of Plexiglas. Velocities in the turbine inlet, mid-, and exit planes were measured as well as five planes in the stator. From the velocity data, non-uniformities and in particular, separated regions were determined. Secondary flows were seen and vorticities were evaluated. Lastly, the torque distribution was found. The torque converter data presented herein embodies the most complete detailed flow data available in the literature for torque converters. With the experimental results as a benchmark, better computational modeling of the internal torque converter flow field can be achieved and the geometries can be optimized to improve the efficiency. In Part I data for the pump were present- ed and analyzed.

APPARATUS

The experimental set-up including the one-directional dual beam backscatter laser velocimetry system was described in detail in Part I of this paper. Thirty-two, 36, and 17 identical blade pas- sages were used for the pump, turbine, and stator, respectively. An overview of the torque converter system is shown in Fig. I. In Fig. 2 the turbine geometry and the measurement planes are shown. The torque converter cylindrical coordinate system is defined as follows: axial - along the torque converter shaft, tan- gential - in the torque converter rotational direction, and radial - perpendicular to the shaft. The pump inlet and exit angles (rela- tive to the axial direction) were -30" and 30°, respectively. The turbine inlet and exit angles (relative to the axial direction) were 61.4" and -63", respectively. The stator inlet and exit angles (rela- tive to the axial direction) were 27' and 70°, respectively.

The torque converter was studied in detail for three speed ratios (0.065, 0.600, and 0.800). Torque converter speed ratio is defined as the turbine speed divided by the pump speed. The oper- ating conditions that were tested are presented in Table I.

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Velocity Measurements in an Automotive Torque Converter-Part 11: Average Turbine and Stator Measurements

1 RATIO I (rpm) I SPEED ( r ~ m ) I ( r ~ m ) 1 ("c) 1

Shell

Fig. 3-Total velocity vectors at the turbine Inlet, rnld-, and exlt planes for SR = 0.800.

Although the LV system was one-directional, different veloci- ty components were measured by rotating the beam splitter and realigning the optics for each component. The axial and tangential velocity components were measured by aligning the laser velocimeter beams perpendicular to the torque converter shaft, while for the radial component the beams were aligned parallel to the shaft. All three components of velocities were obtained.

The instantaneous angular position of the pump and turbine were measured for each valid velocity signal using 9-bit (1024 cir- cumferential positions) shaft encoders on the pump and turbine shafts. Thus, for every valid signal, the velocity, instantaneous rel- ative pump position, and instantaneous relative turbine positions were recorded. Uncertainties in the angular positions of the two rotating components is * 0.35'.

Turbine Measurement Procedure

Measurement locations were determined by first using refer- ence points in the turbine and the known dimensions. The probe volume was then moved to the desired measurement locations in the turbine. Velocity measurements were taken in the inlet, mid-, and exit planes of the torque converter turbine as shown in Fig. 2.

Each blade passage was defined by a pressure and a suction side as well as a core and a shell side.

In all measurement planes, ten evenly spaced measurement locations were accessed between the core and the shell sides and were set by traversing the mill table. For each measurement loca- tion the three velocity components were measured. As the turbine rotated by the stationary laser velocimeter probe volume, all 36 turbine blade passages were accessed. Approximately 30,000 valid velocity samples were collected. This procedure was fol- lowed for all 10 core to shell positions. Using the turbine shaft encoder information, blade-to-blade profiles were generated for all 36 turbine blade passages.

Blade-to-blade profiles were shown to be identical within their measurement uncertainty. Hence, the 36 blade-to-blade profiles were superimposed and averaged to obtain one time-averaged blade-to-blade profile for each core to shell position. The average blade-to-blade profiles were then arranged by their core-to-shell measurement locations and three-dimensional vector plots were generated using commercially available plotting routines. For each of the measured blade-to-blade positions more than 500 valid velocity samples were collected. Repeatability studies and his- tograms showed this to be a sufficient sample size for a high con- fidence in the average velocities. Typical 95 percent confidence intervals of the average velocities were 20.05 mls. Average flow fields in the inlet, mid-, and exit plane at the three speed ratios are shown in this paper.

Stator Measurement Procedure

Measurement locations were determined by first using refer- ence points in the stator and the known dimensions. The probe volume was then moved to the desired measurement locations in the stator. Velocity measurements were taken in the inlet, quarter, mid-, three-quarter, and exit planes of the torque converter stator.

In all measurement planes, ten evenly spaced measurement locations were accessed between the core and the shell sides and were set by traversing the mill table. Also since the stator did not rotate, velocities were measured at ten pressure to suction surface locations by traversing the mill table. As with the turbine, the blade-to-blade profiles of different passages were shown to be identical within their measurement uncertainty. Typical 95 percent confidence intervals of the average velocities were 20.05 mls. Average flow fields in the five planes at the three speed ratios are shown in this paper.

RESULTS FOR THE TURBINE

Turbine time-averaged velocity results are presented and dis- cussed for three measurement planes and three speed ratios. Flow field results are shown as vector plots, secondary flow (velocities tangent to the measurement plane) plots, and through flow contour plots. For the remainder of this paper through flow velocity is defined as the velocity component normal to a given measurement plane. All velocities are presented relative to the rotating turbine frame. From the measurement results, the turbine output torques, average vorticity, viscous dissipation, incidence angles, and exit angles were calculated. Only time-averaged relative velocities are presented herein.

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w

1 I." * S." . a,,. 7 .JI , ..I . > " 6 9." . 9.9. . ." 3 -3. core

P,...""

C o n S h U

Core

[ =3.0 Ws

- * I - .

Pressure

Shell

Shell

Fig. %Secondary velocities In the turbine Inlet and mid- planes for SR = 0.065.

Flg. 4--Through flow veloclty contours at the turblne Inlet, mld-, and exlt planes for SR = 0.800.

Flow Field at the 0.800 Speed Ratio

Typical velocity vector results for the 0.800 speed ratio are shown in Fig. 3 and through flow velocity contours are shown in Fig. 4. Results for the inlet, mid- and exit plane flow fields are pre- sented. 'These plots illustrate general flow trends in the torque con- verter turbine.

Figure 3(a) shows a vector plot of the turbine inlet flow field. For this case the flow enters the turbine with a moderate second- ary flow component from the suction to the pressure side. The pump operates at a tiigher rotational speed than the turbine (opump. w ~ ~ ~ ~ ~ ~ ~ = 220 rpm), causing the pump exit flow to enter the turbine with "pre-swirl." This pre-swirl appeais in the turbine inlet as a secondary flow component from the suction to the pressure side. Typical secondary flow (pre-swirl) velocities for this case are 2.5 mls. 'The through flow velocity distribution for the inlet plane can be observed in Fig. 4(a). Peak through flow velocities of approxi- mately 4.0 m/s are located at the shell side and located near the pressure side. The through flow velocity gradually decreases toward the core side, with minimum velocities of 0.4 m/s located directly at the core. Measurements of the pump flow field by Whitehead and Flack ( 1 999) showed a similar trend in the pump exit plane. The velocity deficit at the pump exit core side was found to be due to flow separation caused by the high radial to axial flow turning angle in the pump. Thus, flow separation in the pump has a noticeable effect on the downstream turbine flow

field. A vector plot of the flow field in the turbine mid-plane is

shown in Fig. 3(b). The through flow velocity distribution for the mid-plane can be observed in Fig. 4(b). Both show a high veloci- ty near the pressure side of the blade centrally located between the core and shell and a low velocity near the suction side, with a small region of back flow. Thus, between the inlet and mid-plane the flow has remained near the pressure side and the velocity deficit near the suction side has not improved. Secondary flows in the mid-plane aie from the pressure suction to the suction side. Tjlpical secondary flow velocities for this case are 1 m/s.

Figure 3(c) depicts the turbine exit plane vector plot of the flow field. The through flow velocity distribution for the exit plane can be seen in Fig. 4(c). Both show a high velocity nearest the pres- surelcore comer. Secondary flows in the exit plane are from the pressure surface to the suction side. Typical secondary flow veloc- ities for this case are 2 d s .

Flow Field at the 0.065 Speed Ratio

Typical velocity results for the 0.065 speed ratio are shown in Figs. 5 and 6(a). For this case the flow enters the turbine with a strong secondary flow component from the suction to the pressure side (Fig. 5(a)). Again, the pump operates at a higher rotational speed than the turbine oPump - otUhi,, = 750 rpm), causing the pump exit flow to enter the turbine with pre-swirl. Typical sec- ondary flow (pre-swirl) velocities for this case are 6 m/s, which is

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Velocity Measurements in an Automotive Torque Converter-Part 11: Average Turbine and Stator Measurements 70 1

pressure and shell sides and reversed flow velocities of 0.3 mls at the core-suction comer. For this case the flow in the plane (sec- ondary flow) is shown in Fig. 5(b). The secondary flow shows a counter-clock-wise rotation with typical velocities of 2 m/s.

Flow Field at the 0.600 Speed Ratio

Fig. +Through flow velocity contours at the turbine mid-plane for SR = 0.065 and 0.600.

9 ) .

d -

G

- 1b

12. " " " " ' " " ' " " ' " " I

0.0 0.2 0.4 0.6 0.8 1 .O

Speed Ratio

Fig. 7-Mass flow rates in the three turbine planes as a function of speed ratio.

larger than for the 0.800 speed ratio due to the larger difference in rotational speeds. The pre-swirl results in large incidence flow angles to the blades. Peak through flow velocities of approximate- ly 5.0 m/s are located at the shell side and located near the pres- sure side. The through flow velocity gradually decreases toward the core side, with minimum velocities of 0.7 mIs (reversed flow) located directly at the core. Again, flow separation in the pump has a noticeable effect on the downstream turbine flow field.

Figure 6(a) presents the mid-plane through flow for the 0.065 speed ratio. A separation region at the core-suction comer can be observed. The separation is due to the pre-swirl and resulting inci- dence angles noted above as well as the velocity deficit at the core due to the pump. Peak through flow velocities of 5.5 m/s near the

Typical velocity results for the 0.600 speed ratio are shown in Fig. 6(b). Once again, the pump operates at a higher rotational speed than the turbine, causing the pump exit flow to enter the tur- bine with pre-swirl. Typical secondary flow velocities for the tur- bine inlet are 4 mls. Peak through-flow velocities of approximate- ly 5.5 m/s are located at the shell side and located near the pres- sure side. The through flow velocity gradually decreases toward the core side, with minimum velocities of -0.1 rnls (reversed flow) located directly at the core. Again, flow separation in the pump has a noticeable effect on the downstream turbine flow field.

Figure 6(b) presents the mid-plane through flow for the 0.600 speed ratio. A separation region at the core-suction corner can again be observed. Peak through flow velocities of 4.9 mls near the pressure and shell sides and reversed flow velocities of 0.3 mls at the core-suction comer. For this case the secondary flow shows a slight counter-clock-wise rotation dominated by a pressure to suction side flow with typical velocities of 2 m/s.

Mass Flow Rates

Mass flow rates for the different planes were calculated by numerically integrating in two directions the average through flow velocities across the passages as for the pump. Results are presented in Fig. 7. Small differences between mass flows between the planes were observed. To evaluate the accuracy of the data an uncertainty analysis of the mass flow rate was performed based on both the uncertainties of the through flow velocities and the uncertainties of the measurement locations. The mass flow rates of all planes were found to agree to within the uncertainty limits as shown in the figure. The mass flow rates were also found to agree with those of the pump within the uncertainty limits.

Secondary Flow Field Analysis

The relative secondary flows in different planes show strong secondary rotational flow patterns. To quantify the fluid rotation- al component the average relative vorticity was calculated using:

where x and y are in the plane directions, and u and v are relative secondary flow velocities in the plane of interest. To integrate the experimental velocity data the expression was rewritten into dis- cretized form as for the pump.

Relative vorticity results for all three speed ratios are present- ed in Fig. 8. Unlike the pump, the results indicate that the vortic- ity is positive throughout the turbine. The vorticity decreases with increasing speed ratio. The vorticity is also highest in the inlet plane.

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R. FLACK AND L. WHITEHEAD

TURBINE -

INLET

con S h l

QUARTER 0.0 0.2 0.4 0.6 0.8 1 .O

Speed Ratio

Fig. 8-Vortlclty In the three turblne planes as a function of speed ratio.

SR=0.065 SR=0.800 lnlet to Mid-Plane Mid-to Exit Plane Inlet to Exit Plane 26.0 21.5

Torque Distribution

The output torque flux of the turbine was calculated using the angular momentum equation:

THREE QUARTER where r is the radius from the shaft center, V, is the tangential velocity component in the stationary frame, V is the total veloci- ty, and p is the fluid density. The surface integral was evaluated numerically for all measurement planes as done for the pump.

Results of the torque between the inlet and mid planes, between the mid and exit planes, and the total output torque (between inlet and exit) are presented in Table 2.

The total output torque at the 0.065 speed ratio is 7.2 N-m higher than at the 0.800 speed ratio. For 0.065 speed ratio the chord-wise torque distribution is uneven; 92 percent of the total torque is extracted between the inlet and the mid-plane. Likewise for the 0.800 speed ratio the torque distribution is unsymmetric (but improved) with 78 percent of the total torque extracted

EXIT

Flg. %Through flow velocity contours at the stator lnlet, quarter, mid, three-quarter, and exit planes for SR = 0.800.

between the inlet and the mid-plane. The uneven torque distribution at the 0.065 speed ratio is

caused by the strong tangential velocity component (pre-swirl) in the secondary flow entering the turbine. For the 0.065 speed ratio case, this flow component is approximately 6 m/s faster than the turbine blade speed. Hence, the tangential flow must be decelerat- ed and redirected by the blades, causing a significant momentum exchange and torque generation on the blades. The momentum

exchange occurs primarily in the first half of the blade passages between the inlet and mid planes. Thus, significantly more torque is extracted between the inlet and mid planes than between the mid and exit planes. For the 0.800 speed ratio the tangential velocity magnitude is smaller but still appreciable (2.5 mls) and conse-

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Velocity Measurements in an Automotive Torque Con verter-Part 11: Average Turbine and Stator Measurements

Fig. 10-Two-D velocity vector profile at five stator core to shell posl- tlons for SR = 0.800.

quently the torque is somewhat more evenly distributed between the inlet and exit planes.

RESULTS FOR THE STATOR

Through flow contour plots were determined for the stator inlet, 114, mid-, 314, and exit planes at the 0.600 and 0.800 speed ratios and for the inlet, mid-, and exit planes at the 0.065 speed ratio. The stator did not rotate. Two dimensional vector plots showing the through flow and tangential velocity components through a stator passage at several core to shell locations are also presented. Only time-averaged velocities are presented herein.

Flow Field at the 0.800 Speed Ratio

'The through flow velocity field in the stator inlet plane of the torque converter is depicted in Fig. 9(a). The flow field is rela- tively uniform. The peak velocity is 2.8 m/s and is located near the center of the plane. Gradual velocity gradients extend toward the pressure and shell sides. A steeper velocity gradient is located on the core side, and the minimum velocity is I .O m/s.

The velocity through flow profile in the stator quarter plane is presented in Fig. 9(b). The peak velocity is near the suction side (3.8 m/s). The flow field is relatively uniform with an average velocity of 2.7 m/s, and is similar to that of the stator inlet plane, except along the suction side. Highest velocities are found along the suction side and decrease toward the pressure side. The mini- mum velocity in the quarter plane is 0.6 m / ~ . A strong velocity gradient on the pressure side of the quarter plane is present.

Through flow velocities continue to decrease between the suc- tion and pressure sides in the stator mid-plane, Fig. 9(c). The peak

Fig. 11-Through flow velocity contours at the stator Inlet and exlt planes for SR = 0.065.

velocity in the mid-plane is 5.5 m/s, and is located along the suc- tion side. The mid-plane velocity profile is very similar to the quarter plane profile, except the flow field is slightly less uniform with a slight positive gradient from pressure to suction surfaces.

The through flow profile of the three-quarter plane is present- ed in Fig. 9(d). The peak velocity is 4.8 m/s, and is at the 70 per- cent core to shell, 80 percent pressure to suction position of the plane. Velocities decrease toward the pressure and core sides, and a steep velocity gradient is located in the suction-shell comer, with a minimum velocity of 0.2 m/s in this region. Also, a slight gradi- ent is found in the pressure-core comer.

In the stator exit plane, the high velocity region noted in the stator 314 plane shifted to the shell side, at the 30 percent pressure to suction position, Fig. 9(e). The peak velocity is 4.3 m/s. Velocities decrease toward the pressure, core, and suction sides. A separation region occupying about 20 percent of the plane is found at the suction-shell comer, and the minimum velocity is -0.2 m/s.

Figure 10 shows the 2-D flow field through a stator blade pas- sage at the 5 percent, 25 percent, 55 percent, 75 percent, and 95 percent core to shell locations. These plots show the measured through flow and tangential velocity components, at the stator inlet, mid, and exit planes. The flow is relatively uniform and well aligned with the blades at the inlet plane at all five core to shell locations. Some flow turning is evident at the mid-plane. At the mid-plane the flow increases across the passage from the pressure side to the suction side; the maximum velocity occurs on the pres- sure side at'every core to shell position. The flow separates on the suction side at the stator passage exit near the shell. This separa- tion was also noted in Fig. 9(e).

Flow Field at the 0.065 Speed Ratio

The stator inlet plane flow field is shown in Fig. 1 l(a). A high

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Fig. 12-7Lvo-D velocity vector profile at five stator core to shell posl- tlons for SR = 0.065.

velocity region is located on the suction side, and the velocity decreases toward the pressure side. The peak velocity is 5.1 d s . A significant low velocity region on the core side is observed, occupying approximately 15 percent of the plane. The minimum vclocity is -0.3 m/s.

The through flow field in the stator mid-plane was also meas- ured. A region of uniform, high velocity flow is located near the center of the plane, and extends toward the suction and shell sides. The peak velocity is 8.1 m/s. Velocities decrease sharply along the shell and core sides and near the suction-shell corner. Low veloc- ity regions are located in the suction-shell corner and, as in the inlet plane, on the core side at about 70 percent of the suction to pressure distance. The minimum velocity is -1.2 d s . A weaker negative velocity gradient occurs between the high velocity region and the pressure-core corner.

The peak velocity in the stator exit plane is 7.0 mls, and is located at 35 percent of the core to shell distance, and 55 percent of the suction to pressure distance, Fig. 1 I (b). Through flow veloc- ities decrease in all directions, with the sharpest gradient occuning toward the core side. Large low velocity regions are found on the core and suction sides, and the minimum velocity is -0.5 m/s.

Figure 12 shows the flow field through a stator blade passage at the 5 percent, 25 percent, 55 percent, 75 percent, and 95 percent core to shell locations. These plots again show the measured through flow and tangential velocity components, at the stator inlet, mid, and exit planes. At all core to shell locations, the flow enters the stator at a large negative incidence angle. The flow entering the stator at the 0.065 speed ratio is much more mis- aligned with the blades than at the 0.800 speed ratio. A high veloc-

Fig. 13-Through flow velocity contours at the stator inlet and exit planes for SR = 0.600.

ity region on the suction side of the inlet plane is shown in Fig. 12. In the stator mid-plane the highest velocity flow migrates from the suction side to 50 percent of the suction to pressure distance from the core to the shell. A separation region is noted near the core, resulting from the misaligned flow at the inlet. Also at the mid- plane, the flow has turned significantly. This direction reversal imparts torque on the flow, and indicates the desired presence of torque multiplication at the low speed ratio. In the exit plane, as seen in the through flow contour plot, the through flow velocity is lowest on the passage suction side from core to shell, with the lowest velocity near the core.

Flow Field at the 0.600 Speed Ratio

The through flow results in the stator inlet plane at the 0.600 speed ratio are presented in Fig. 13(a). A high velocity region is located on the suction side, with a peak velocity of 4.4 d s . Velocities decrease toward the pressure side. The minimum veloc- ity is 0.9 d s , and is located on the core, at the 30 percent pressure to suction location. The average velocity is 2.4 d s . The location and magnitude of the high velocity region in the inlet plane is very similar to that in the inlet plane at the 0.065 speed ratio.

The maximum velocity in the stator quarter plane is 7.4 d s , and is located on the suction side, and at approximately 65 percent of the core to shell distance. The through flow velocity has increased from the inlet plane. The velocities decrease toward the pressure side, and a sharp gradient is located near the shell side. The decrease in velocity across the plane, however, is quite uni- form, and is similar to that found in the inlet plane. The minimum velocity is 0.3 d s , and is located in the pressure-core comer.

In the stator mid-plane, the high velocity region is closer to the core side, and is on the suction side of the plane. The peak veloc- ity is 7.2 d s . A very steep velocity gradient is apparent on the shell side, but throughout the rest of the plane through flow veloc-

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Velocity Measurements in an Automotive Torque Converter-Part 11: Average Turbine and Stator Measurements

Speed Ratio

Flg. 14--Mass flow rates In the five stator planes as a function of speed ratlo.

TABLE 3-STATOR TORQUES (N-m)

SR=0.065 SR=0.800 Inlet to Mid-Plane Mid-to Exit Plane Inlet to Exit Plane

ities decrease uniformly toward the pressure side, as seen in the stator quarter plane. The minimum velocity in the mid-plane is 0.8 m/s, and is located in the pressure-core comer.

In the 314 plane, the high velocity region is located at the 60 percent pressure to suction, 85 percent core to shell location; the peak velocity is 6.9 mls. Velocities decrease between the shell and core sides, and are fairly uniform between the pressure and suc- tion sides except for a sharp negative gradient at the suction-shell comer. The minimum velocity in the 314 plane is 0.9 d s , and is located in the suction-shell comer. The flow field at this speed ratio is very similar to that found at the 0.800 speed ratio.

Figure 13(b) depicts the flow field at the stator exit plane. A large velocity deficit region encompassing approximately 30 per- cent of the plane occurs at the suction half of the plane with a min- imum through flow velocity of -0.5 d s (separated). The stator exit blade angle relative to the axial direction is fairly steep, thus causing the flow to separate on the suction side. The peak veloci- ty is 6.9 mls, and is located in the high velocity region positioned on the pressure side, at about 85 percent of the core to shell dis- tance. A similar region was observed at the 0.800 speed ratio.

Mass Flow Rates

Mass flow rates for the different planes were again calculated by numerically integrating the through flow velocities across the passages, as for the pump and turbine. Results are presented in Fig. 14. Differences between mass flows between the planes were observed but were found to agree to within the uncertainty limits as shown in the figure. The mass flow rates were also found to agree with those of the pump and turbine within the uncertainty limits.

Torque Distribution

The input torque flux of the stator was calculated using a dis- cretized equivalent to the angular momentum equation. Results of the torque between the inlet and mid-planes, between the mid-and exit planes, and the total output torque (between inlet and exit) are presented in Table 3.

The total torque delivered to the working fluid at the 0.065 speed ratio is 8.1 N-m and much higher than at the 0.800 speed ratio. At the low speed ratio a significant amount of torque is developed in the stator, indicating the presence of torque multipli- cation. For the 0.065 speed ratio the chord-wise torque distribu- tion is relatively even; 63 percent of the total torque is delivered to the fluid between the inlet and the mid-plane. For the 0.800 speed ratio the torque distribution between all planes is minimal, indicating minimal torque multiplication, the expected effect in the stator at high speed ratios.

It is worthy to note that the sum of all of the torques delivered to the fluid (stator and pump) is within the uncertainty (* 2.0 N- m) of the torques derived from the fluid (turbine) at both speed ratios.

CONCLUSIONS

Laser velocimetry was used to measure the flow field in the turbine and stator of an automotive torque converter. The data complements that of data in a pump at the same operating condi- tions. Average velocities are presented and analyzed in this paper for three turbinelpump speed ratios (0.065, 0.600, and 0.800). Data presented in this paper embody the most detailed velocity measurements in torque converters available. Important specific conclusions drawn from this investigation are:

Turbine

1. In all measurement planes and at all speed ratios the highest through flow velocities generally occurred at the pressure side of the channel. A velocity deficit near the core was observed at the turbine inlet. This is due to the velocity deficit at the pump exit that transmits to the turbine inlet. At a speed ratio of 0.065 flow entered the turbine with signifi- cant "pre-swirl" causing the flow to separate on the suction surface between the inlet and the mid-plane, resulting in a separation region in the core-suction quadrant.

2. Strong circulatory secondary flows were not observed in the turbine planes as they were in the pump planes. The meas- ured vorticity was highest at the inlet plane.

3. The torque distribution was found between the inlet and mid- planes and mid- and exit planes. The chord-wise distribution was uneven and between 78 percent and 92 percent of the

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torque was derived from the fluid between the inlet and mid- plane.

Stator

I . The flow field is relatively uniform at the inlet at the 0.800 speed ratio but much less so at the speed ratios of 0.065 and 0.600. Some separation is seen at the lowest speed ratio at the inlet (near the core). At the highest speed ratio flow enters the stator with little incidence to the blades. At lower speed ratios significant incidence was measured resulting in separation on the suction surface. For the highest two speed ratios a significant separation region was observed at the exit in the suction/shell quadrant. Such separation is unde- sirable in any turbomachine as it will result in steady and unsteady loads on the tribological components, such as bearings and seals and reduce the expected lives of these components due to fatigue.

2. The torque distribution was found between the inlet and mid- planes and mid- and exit planes. The total torque delivered to the working fluid at the 0.065 speed ratio is significant, indicating the presence of torque multiplication. At the 0.800 speed ratio the torque distribution between all planes

is minimal, indicating minimal torque multiplication. For the 0.065 speed ratio the chord-wise torque distribution is relatively even; 63 percent of the total torque is delivered to the fluid between the inlet and the mid-plane. The sum of all of the torques delivered to the fluid (stator and pump) is within the uncertainty of the torques derived from the fluid (turbine). Again, an unbalance of torques will lead to can- tilever modes or non-uniform loads on the tribological com- ponents and reduce the expected lives of these components.

ACKNOWLEDGMENTS

This research was sponsored by General Motors Corporation Powertrain Division. The authors wish to express their gratitude to D. Maddock for his technical and hardware support.' The research was also supported in part by the Rotating Machinery and Controls Laboratory at the University of Virginia.

REFERENCES ( I ) Whitehead, L.D. and Flack. R.D. "Velocity Measurements in an Automotive

Torque Convener Pan I - Average Pump Measurements," Tribology Transactions, 42. 3, pp. 687-696, (1999).

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