Thermal stratification in LH2 tank of cryogenic propulsion stage tested in ISRO facility Presentation to ICEC26-ICMC th March 2016 M Xavier, Division Head Dr V Narayanan, Deputy Director Liquid Propulsion Systems Centre ISRO, Thiruvananthapuram Oral Id-8-O-2C-1

Contents GSLV-MkII vehicle integrated with Cryogenic Upper Stage

 LOX & LH2 tanks  Structural elements  LOX & LH2 fluid circuits  LOX & LH2 umbilical units  Cryogenic gas bottles  Thermal insulation  Command system  Safety system  Cryogenic engine  Control system 1. Configuration of cryogenic upper stage of GSLV-Mk II GSLV-MkII vehicle integrated with Cryogenic Upper Stage After its successful ground testing in 2007, flight testing of CUS-05 was accomplished in GSLV-D5/GSAT-14 mission on 5 th Jan 2014

2. Test objectives and test sequence of stage hot test conducted in ISRO facility  Test objectives : -Filling of specified mass of LOX&LH2 in tanks -Chilling of turbo pumps of engine with cold GHe and respective propellants -To supply LOX&LH2 at specified pressure to engine inlet from respective tanks -To study stratification in tanks -To demonstrate engine operation for 720s Tank pr., MPa Liquid Outflow, lps Pressurant gas used 0.238H2 gas at 200K He gas at 90K Engine chamber pr, MPa = 5.8 Mixture ratio = 5.8 Thrust uprating = 11% Area ratio = 198

3. Stratification in cryogenic propellant tanks a)Constant wall temperature (T w ) Boundary layer transition Ra 10 9 → Turbulent β = Volumetric thermal expansion coeff. θ w = Wall to bulk temperature difference b) Constant heat flux (q w ”) Boundary layer transition Modified Ra →Turbulent

To finalise LH2 tank pressure for cavitation free operation of Turbo pumps of cryogenic engine, stratified layer temperature should be known. P t = P sat (Ts) + P NPSP + P NPSP(margin) + Pr. drop P t = Tank pr. to be maintained by pressurization system P sat (Ts) = Sat. pressure of liquid stored in LH2 tank P NPSP = Net positive suction pressure of turbo pumps Pr. drop = Pr. drop in feed line from tank to pump inlet 4. Need for predicting stratified layer temperature Ts(t) in LH2 tank Dump Nozzle Tank pressure rise due to stratification is critical for self pressurised tanks. This will result in premature venting of hydrogen gas from LH2 Tank in atmospheric flight of cryogenic stage-causing safety issues. a) b)

5. Analytical model for stratification a) Methodology for predicting Stratified layer thickness ∆(t) with constant heat flux Growth of stratified layer depends on mass flow rate of warm fluid from boundary layer to liquid stratum u (y) depends on nature of boundary layer.

b) Methodology for predicting Stratified layer thickness ∆(t) with constant wall temperature

Time (s) T sat, K ∆(t) Measured, m ∆(t) Computed, m T T T Thickness of stratified layer 6. Experimental data on stratification in LH2 Tank

Stratified layer temperature Ts(t) and its gradient in liquid column Solution based on 1-D Semi-infinite solid model approach Heat transfer from warm pressurant gas to stratified layer

Measurement of temperature gradient of stratified layer at the tank centre using an array of temperature sensors mounted on a FLOAT Comparison of experimental results with CFD results. Improved model considering stratification on Isogrid/ waffle surfaces instead of plain wall. On these surfaces boundary layer thickness will be more. 6. Future Work Analytical work is to be extended to consider spin rate of cryogenic stage, ω =1 0 /s, of stage and the associated sloshing of liquid surface on stratification. This increases boundary layer run length (x) and increases stratification.

7. Conclusion  Stratified layer temperature is in equilibrium with LH2 tank pressure which varies during the test.  Computed stratified layer thickness Δ(t) is 0.44 m over 720s and shows a reasonable match with the experimental data at different intervals.  Temperature gradient in stratified layer is over a thickness of 0.05m as per model results. An array of temperature sensors is to be provided at the center of the tank to capture the temperature gradient in stratified layer.  The analytical model can be improved by incorporating isogrid/waffle construction on the tank inner surface.