Pacific Marine Science Report 80-6

DATA REPORT AND CALIBRATIONS FOR TURBULENCE MEASUREMENTS IN KNIGHT INLET, B.C. FROM THE PISCES IVSUBMERSIBLE: NOVEMBER 1978

by

A.E. Gargett

INSTITUTE OF OCEAN SCIENCES Sidney, B.C.

Pacific Marine Science Report 80-6

DATA REPORT AND CALIBRATIONS FOR

TURBULENCE MEASUREMENTS IN KNIGHT INLET, B.C.

FROM THE Pisces IV SUBMERSIBLE: NOVEMBER 1978

by

A.E. Gargett

Institute of Ocean Sciences Sidney, B.C.

1980

i

Abstract

The main purpose of this report is to archive cal ibration t echniques and results for the set of sensors used on the Pisces IV submers ible in November 1978 . At that t ime , a series of measurements in Knight Inl et , British Columbia sampled turbul ent velocity and temperature fields associated with three different regimes : a nonlinear internal wave train , a near- surface shear zone downstream o f an internal hydraulic j ump , and the shallow waters of the inl et in the absence of internal hydraulic events . Cal ibrated analog data is presented .

ii

TABLE OF CONTENTS

Abstract

Table of Contents

1 . Introduct ion

2 . Cal ibration

2 . 1 Heated p lat inum film : u

2 . 1 . 1 2 . 1 . 2 2 . 1 . 3 2 . 1 . 4 2 . 1 . 5

The hot -film as a mean flow sensor Sensit ivity calibrations Frequency-response cal ibrations Angul ar response Temperature sensit ivity

2 . 2 Cold platinum film : T '

2 . 2 . 1 2 . 2 . 2

Sensitivity calibrat ions Frequency-response cal ibrations

2 . 3 Airfoil probe : v and w

2 . 3 . 1 2 . 3 . 2 2 . 3 . 3

Principle of operation ; s ensitivity cal ibration Effect of temperature on probe sensitivity Frequency/wavenumber response

2 . 4 Conductivity

2 . 5 Thermistors

2 . 6 Rotor current meters ; U, V, and W

2 . 6 . 1 2 . 6 . 2

Head-on cal ibration Angle-of-attack cal ibrations

2 . 7 Pressure gauge

2 . 8 Accelerometers

3 . Measurements

4 . Acknowledgements

page

i

i i

1

3

3

4 6 7 8 9

1 0

1 1 1 1

1 3

1 3 1 5 1 5

1 6

1 7

1 8

19 19

22

2 3

25

27

iii

5 . Appendix : Tab l es 29

Tab l e AI : Probe l ist , all dives ; Tapes 815-844 are Knight Inlet dat a . 3 1

Table A2 : Data channels and sample rates . 3 2

Tab l e A3 : Pisces dive information ; Knight Inlet , B . C . , November 1978 . 33

6 . References 35

7 . Figures 37

1

1 . Introduction

The complete turbul ence system for the Pisces IV submersib l e has been under development for some years , s ince an initial maj or modification necessary to stab i l i z e the submersible for mid-water running . Figure 1 documents the growth of a severe pitch instab il ity after ful l power was appl ied to the thrusters us ed to propel Pisces . The ampl itude of the pitching motion quickly reached 20o and might have gone higher sti l l : such tests were inevitab ly halted due to personnel discomfort . This instability has been compl etely removed by the des ign (by Dr . G . Parkinson of the Mechanical Engineering Department , Univers ity of British Columbia) of a set of removab le stabilizing wings , shown schematical ly in Figure 2 , and in a photograph (Figure 3) taken from the rear of the submersib l e . The plane of the flat control section of the wings can be varied b etween approximately -2 and +10 degrees from hori zontal : smal l adj ustments in wing angle al low the pilot to drive Pisces s lowly up and down through the water column without adj usting the thruster angles , hence without changing the mean forward speed of the submersibl e through the water . Subsequent addition o f an hydraulica l ly contro l led trim tab on one o f the vertical s ections of the wings (see Figure 3) al lowed us to remove a slow d irectional drift which proved annoying in operations . With addition of this contro l apparatus , the submers ibl e has proven a flexib le vehicle for turbulence measurements; its mot ion through the water column i s such that the mean forward speed is relatively constant and mean cross-flows at the s ensor package are relatively smal l , except when it is necessary to carry out some manoeuvre such as change of hori zontal direction or the rapid change of attitude required to avoid breaking the water surface at the top of a gradual ascent through the water column .

Sensors are mounted at the end of a forward strut (see Figure 2) , as far forward of the personnel sphere as is operationaly practical . The high- frequency turbulence sensors l ead the rest (as shown in the ins ert to Figure 2) , roughly 3 m in front of the personnel sphere . The direction of mean forward speed U is defined along the axis of the sensor package , positive toward the submers ible; cross-axis flows are defined to comp l ete a right-handed coordinate system with W positive upwards . These flows are measured at the locat ion of the sensor package : s ignal s from three smal l rotor current meters designated A , B , and C in Figure 2 are combined and rotated to given U, V , and W . A conductivity-temperature s ensor C-TA, coupled with the depth gauge on the submers ibl e , al lows determination of mean temperature and sal inity at the l evel of the high-frequency sensors , whi l e an additional thermistor TB at a vertical s eparation of 0 . 8 m provides an estimate of the mean vertical temperature gradient . The high frequency sensors were mounted 0 . 33 m in front of these auxiliary sensors in the order shown in the insert to Figure 2 . Axial component of velocity (u) was sensed with a heated conical platinum film probe , temperature (T ' ) with a cold conical platinum film, and cross-flow velocity components (w and v) with two s ingl e- channel airfoil probes . These probes were mounted as close together as pos s ib l e : s eparations were (u - T) = 0 . 6 cm , (T - w) = 3 . 7 cm , and w - v) = 1 . S cm. A set of three orthogonal accel erometers mounted immediately behind the high frequency s ensors and a pres sure gauge in a separate pressure case closer to the personnel sphere (neither shown in Figure 2 ) comp l eted the instrumentation carried outs ide the submers ib l e .

2

Voltages from al l s ensors entered the personnel sphere through an el ectrical penetrator , and were then digiti zed and recorded by a specially-designed data system (SCRIBE) which has been described in some detail by Gal loway and Teichrob (1979) .

This system was successful ly used for the first t ime in November 1 978 during a s eries of dives in Knight Inlet , one of the fj ord-type inl ets of the British Columbia coast . A submarine si l l across the inlet produces a variety of internal hydraulic phenomena (Farmer and Smith , 1980) including a strongly nonl inear and highly turbulnt internal wave train which progress es up inlet twice a day , shortly after the t ide turns to flood across the si l l . Although the internal wave train was the primary obj ective of this s et of measurements , a few diving days were spent investigating flow downstream of the s i l l on the ebb tide , when a strong first-mode internal hydraul ic j ump was pres ent over the si l l itself (D . Farmer, personal communication) .

The main purpos e of this report is to archive calibrations of al l the instrumentation used for the Knight Inlet measurements , including a discussion of cal ibration techniques when these are unique or not described in other publications . Lists of s ensors , sample rates , dive locat ions , etc . are given as tables in the Appendix . Cal ibrations are found in Sect ion 2 , whi le Section 3 contains a brief discussion of dive locations and data qual ity as revealed by examples of (cal ibrated) analog records .

3

2 . Cal ibrations

2 . 1 Heated platinum film : u

The axial component u of the turbulent velocity field is s ens ed with a heated platinum film probe . The s ensing element is a thin ring of plat inum depos ited around a conical glass probe and protected by a very thin quartz coating . E l ectrical current passing through the platinum fi lm raises its temperature above ambient by an amount T referred to as the overheat . Fluctuations in current speed parallel to the probe axis produce fluctuations in heat transfer from the fi lm , which may be s ensed by a bridge de,signed to operate in either constant current or constant temperature mode . The latter is more appropriate for applicat ions in the ocean , where plankton or detrital materials frequently lodge on the probe and greatly reduce the heat transfer : constant current operation would burn out the probe under these circumstances . Short probe l ifetime due to sea-water corrosion of the platinum film has not b een a significant prob lem s ince developments of quart z coating techniques for the probes and an AC bridge circuit ( laboratory appl ications of hot-fi lm techniques in fresh water invariab ly Use DC bridges ) . We have used individual probes for many days of field operation . Indeed , we are still using probes from the s et manufactured in the 1960s at the University of British Co lumbia for the Pacific Naval Laboratory (now DREP , Defence Res earch Establishment , Pacific) , and used by Grant , Stewart and Moi l 1 iett ( 1 962) in their pioneering measurements of high Reynol ds number , turbulence in a tidal channel . These probes have stable cal ibrations ( see cal ibrat ions of V30 in this s ection) and , if not physical ly damaged, wi l l operate for many hours . One of